Evolutionary Psychology: An Introduction (2021) offers a comprehensive exploration of how Darwinian principles shape the human mind and behavior. Grounded in modern research, it bridges biology and psychology to explain universal mental adaptations.

FULL SUMMARY

About the Authors:
Lance Workman is a psychologist and professor specializing in evolutionary psychology, with a DPhil from the University of Sussex and extensive media and academic contributions.
Will Reader is a senior psychology lecturer at Sheffield Hallam University whose research focuses on social media, technology, and evolutionary theory.
Workman and Reader also edited The Cambridge Handbook of Evolutionary Perspectives on Human Behavior

1: Introduction to Evolutionary Psychology

Evolutionary psychology applies principles of Darwinian natural selection to understand the human mind.

Natural selection is based on differential reproductive success of heritable characteristics that vary in a population.
The human mind, as a physical organ (the brain), is shaped by natural selection, and thus, behavior is also a product of evolution.

The key premise is that the mind, like the body, has evolved to solve problems faced by our ancestors in the Environment of Evolutionary Adaptedness (EEA).

Key Concepts

• The Environment of Evolutionary Adaptation (EEA): The ancestral environment in which human psychological traits evolved, shaping our current behavior and cognition.
• Proximate and ultimate levels of explanation: Proximate explains how a trait works (mechanism), while ultimate explains why it evolved (function/adaptive value).
• Heritable variability: Differences in traits among individuals that can be passed down genetically.
• Differential reproductive success: The idea that some traits increase the chances of reproducing and passing on genes more than others.
• Particulate inheritance: The principle that genes are passed on as discrete units, not blended (Mendelian genetics).
• Eugenics: A controversial and discredited movement aimed at improving the genetic quality of a population, often through unethical means.
• The Great Chain of Being (scala naturae): A historical, hierarchical concept ranking all living things from lowest to highest (e.g., minerals to God), not supported by modern biology.
• Sociobiology: An approach that applies evolutionary theory to explain social behavior, often criticized for being overly genetic determinist.
• Gene–culture co-evolution / dual-inheritance theory: The view that genetic and cultural evolution interact and shape each other over time.
• Naturalistic fallacy: Mistakenly assuming that what is natural is morally right or desirable.
• Moralistic fallacy: Mistakenly assuming that what is morally desirable must also be found in nature.

A History of Evolutionary Thinking

1. Erasmus Darwin and Jean-Baptiste Lamarck proposed early evolutionary ideas; Lamarck’s inheritance of acquired characteristics is largely discredited, though epigenetics offers a modern but limited twist (Haig, 2007).
2. Charles Darwin’s On the Origin of Species (1859) introduced natural selection via heritable variability and differential reproductive success, with The Expression of the Emotions in Man and Animal (1872) extending this to mental processes.
3. Gregor Mendel’s particulate inheritance (1865) laid genetics’ foundation, later integrated into the modern synthesis with Darwin’s work.
4. William James (1890) highlighted human instincts, countering views of humans as instinct-free compared to animals.
5. Francis Galton (1908) pioneered psychometrics and eugenics, applying evolution to psychology, though eugenics remains controversial.
   • Quote:
     More controversial was Galton’s attempt to apply his scientific findings to help the greater good of society.
     He suggested society might be improved (with) a little selective breeding. He suggested that individuals who might benefit society (the innovators, the highly intelligent etc.) be encouraged to produce many offspring, and those whose traits are seen as less desirable (the less intelligent, the indolent etc.) be discouraged from reproducing, a controversial programme that he called eugenics
6. Sigmund Freud’s (1914) id and unconscious motives align with genes influencing behavior.
7. The Standard Social Science Model (SSSM) dominated 20th-century social sciences, viewing humans as blank slates shaped by culture, reacting against biological determinism (Tooby & Cosmides, 1992).

Addressing Misconceptions

• “More Evolved” Fallacy (Great Chain of Being): The idea that some organisms are “more evolved” or that humans descended directly from chimpanzees and we’re an ‘upgraded species’ is a misunderstanding. Instead, humans and chimpanzees share a common ancestor, and each species possesses unique adaptations suited to its evolutionary path
  🙋🏼‍♂️ Lucio’s note: this is also similar to the misconception that evolution ‘always moves towards a better version’, which is not always the case
• Nature VS nurture fallacy: The field seeks to unify social sciences through Darwinian principles, acknowledging the impact of both nature and nurture, both of which also co-influence each other
• Genes are ‘inflexible’: Genes must not necessarily lead to behaviour that is fixed and inflexible; flexibility is often built into the system, with behaviour being contingent upon the environment and genes, biology, culture and environment all influencing each other
• Evolutionary psychology is ‘bad’: We must not reject it simply on the grounds that some people have used it for nefarious means, any more than we should reject sub-atomic physics for its role in the production of nuclear weaponry. The fact that we do not like the implications of a particular theory does not affect its truth

Methods for Reviewing Evolutionary Theories

1. Behavioural Genetics

This method uses twin and adoption studies to estimate how much genes contribute to various traits by comparing genetically identical individuals (e.g., monozygotic twins) with those who are not (e.g., dizygotic twins or siblings). While it helps establish heritability, it does not indicate whether a trait is an adaptation shaped by natural selection.

• Estimates genetic vs. environmental influences on traits (e.g., intelligence, personality, obesity, addiction).
• A genetically influenced trait is not necessarily adaptive.

2. The Comparative Method

This method examines whether similar ecological problems are solved in similar ways across species, particularly between humans and closely related animals like apes. It helps identify potentially adaptive behaviours by comparing with animals still living in environments similar to those of ancestral humans.

• Looks for functional analogies between humans and non-human species.
• Easier to evaluate adaptive value in non-human animals because their ecological context often mirrors ancestral conditions.
• Traits can be judged adaptive if they lead to increased reproductive success in these contexts.

3. Cross-Cultural Research

Cross-cultural comparisons test whether certain traits are universal across human societies, suggesting an evolved basis. It also addresses the heavy sampling bias in psychology research, which overwhelmingly draws from WEIRD populations (Western, Educated, Industrialized, Rich, Democratic; Henrich, Heine & Norenzayan, 2010).

• Universal traits may indicate evolutionary adaptations.
• Recognizes that some evolved traits only manifest under specific environmental conditions.
• Special focus is placed on hunter-gatherer societies, whose ecological conditions are thought to be closer to those of ancestral humans.
  • Example: Research into male aggression as an adaptation for mate competition is tested by observing reproductive success among more vs. less aggressive men in these societies.

4. Computational Modelling

This involves building abstract simulations where computer-based agents with different traits “compete” under evolutionary rules. It allows exploration of trade-offs and strategy dynamics that would be difficult to observe in real life.

• Models how different strategies perform in scenarios like competition for food or mates.
• Example: The hawk-dove game simulates cost-benefit trade-offs of aggression vs. submission (Maynard Smith, 1974).
• The most successful strategies (those that lead to the most “offspring”) help identify potential evolutionary stable strategies.
• Also used to study cooperation (Axelrod, 1984), personality differences, and cultural evolution (Laland, 2017a).

5. Palaeontological Evidence

Although behaviour doesn’t fossilize, ancient physical evidence—like skulls, tools, and art—offers indirect insights into ancestral behaviour, cognition, and social structure.

• Skull interiors provide evidence of possible language capabilities.
• Burial practices suggest social structures, warfare, or gendered reproductive strategies.
• Artefacts like tools and cave art indicate ritual, aesthetic sense, and possibly symbolic thinking.
• Evidence of art among Neanderthals (e.g., 60,000-year-old hand stencils dated with uranium-thorium; Hoffman et al., 2018) raises questions about cultural transmission or parallel evolution.

Additionally, metaphorical “fossils” may exist in our minds.
For instance, preferences for certain landscapes (e.g., rolling hills, rivers, vegetation) might be evolved adaptations for habitat selection, suggesting a universal aesthetic preference rooted in ancestral survival needs (Dutton, 2009).

Disciplines Applying Evolutionary Thinking

The authors outline five key disciplines that integrate evolutionary thought into the study of behavior, acknowledging their overlaps:

• Ethology: Observes animal behavior naturally, blending evolutionary and causal explanations (Lorenz, Tinbergen emphasized instincts; later focus on gene-environment interactions).
• Behavioral Ecology: Predicts behavior via cost-benefit models (e.g., foraging, mate-seeking), optimizing inclusive fitness with gene-driven flexibility.
• Sociobiology: Applies evolution to social behaviors like altruism and cooperation. Overlaps with behavioural ecology – in fact most of the names listed under sociobiology could also appear under behavioural ecology and vice versa.
• Evolutionary Psychology: Examines psychological adaptations shaped by evolutionary pressures.
  Lucio’s note: Mesoudi in The Cambridge Handbook states it emerged in the 1990s as a fusion of sociobiological theory and cognitive science (Barkow et al., 1992; Buss, 2009; Pinker, 1997)
  Like sociobiology draws on ethology and behavioural ecology, but focuses on mental states rather than behaviour per se, emphasizing a mismatch between current and evolutionary environment
• Cultural Evolution: Studies cultural practices’ evolution, akin to natural selection.

Main Ideas

Workman and Reader assert that evolutionary psychology bridges biology and psychology, offering ultimate explanations for behaviors that complement proximate analyses.

• Proximate VS ultimate explanations: proximate (how behaviors develop, e.g., biological mechanism) and ultimate (why behaviors exist, e.g., survival benefit) explanations differentiate traditional psychology from evolutionary approaches (Darwin, 1860).
• Controversies: Sociobiology (Wilson), eugenics, and politically charged debates. EP is criticized for being deterministic, reductionist, or politically motivated.
• The modular mind: The mind is composed of evolved, domain-specific modules (Cosmides & Tooby).

2: Principles of Evolutionary Change

This chapter explains how genetic inheritance underpins evolution and behavior, detailing mechanisms like natural selection, genetics, and epigenetics as the biological foundation for evolutionary psychology.

Natural selection, genetics, and epigenetics form a robust framework for behavioral evolution, with Genome-Wide Association Study (GWAS) highlighting that many genes are at play for most major traits (polygenic influences), and with gene-environment interplay.

Personality and intellectual ability are genetically inherited.
Given that a third of all protein-coding genes are expressed only in the brain (i.e. they only produce proteins here) many behavioural biologists believe that differences in personality and intellectual ability may, in part, be traced back to differences in the genetic code that we inherit from our parents (Plomin et al., 2016)

Key Concepts

• Natural Selection: The cornerstone of evolutionary theory, natural selection, is explained as the differential survival and reproduction of individuals due to differences in phenotype.
  Traits that enhance survival and reproduction in a given environment are more likely to be passed on to subsequent generations.
  • Individual selection: Natural selection operating on individual traits that increase personal fitness.
  • Group selection: The idea that natural selection can act on groups, not just individuals. Largely discredited in its original form
  • Gene selection: The view that evolution acts at the level of genes, favoring those that replicate successfully.
  • The selfish gene: Richard Dawkins’ concept that genes act in ways that maximize their own replication, even if this appears altruistic.
• Genes: Units of heredity made of DNA that code for proteins and influence traits..
  • Pleiotropic genes affect more than one trait or characteristic (i.e., it has multiple phenotypic effects). Many traits and most personality traits are ‘pleiotropic’, depending on many genes
  • Antagonistic pleiotropy: a single gene has multiple effects—some beneficial and some harmful—depending on the context, especially across different stages of life. For example, testosterone shortens men’s lives but gives them broader chests and greater upper-body strength in early adulthood.
    It also means there may be no benefit for females living longer – this is simply a side effect of less testosterone.
  • Chromosomes: Structures within cells that carry genes; humans have 23 pairs.
  • DNA: The molecule that carries genetic information in all living organisms.
• Genes and Inheritance: Covers Mendelian genetics (segregation, alleles, meiosis, mitosis), protein production from DNA, and human genetic similarities, driving heritable variation (Mendel, 1865).
• Heritable variation: Differences in traits that can be passed from parents to offspring via genes.
• Fitness: an organism’s ability to survive and reproduce in its environment, passing on its genes to the next generation.
  • Reproductive success: The number of viable offspring an individual produces, contributing to the next generation.
  • Inclusive Fitness: Extends reproductive success to kin, explaining altruism (Hamilton, 1964).
• Mendelian genetics: Principles of inheritance based on Gregor Mendel’s work, explaining dominant and recessive traits.
• Genotype VS Phenotype: Genotype is genetic makeup of an organism, while the phenotype are the observable traits of an organism, shaped by genes and environment.
• Mutation: A random change in DNA that can introduce new genetic variation.
• Heritability of characteristics: The proportion of trait variation in a population due to genetic differences.
• Genome-wide association: A method that scans genomes to find genetic variants linked to traits or diseases.
• Behavioural epigenetics: The study of how environmental factors can change gene expression and affect behaviour.
• Mutation and Genetic Drift:
  • Random mutations introduce new genetic variation, happens inside an individual organism—for example, when a cell divides and copies DNA, sometimes a “typo” (mutation) occurs in the gene sequence. This creates new genetic variants (alleles) that were not there before.
  • Genetic drift happens at the population level, across generations without being selected for and due to chance events in who reproduces and passes on genes.
    It mostly affects smaller populations because in larger populations non-random, fitness-increasing mutation tend to win out
• Behavioural Epigenetics: A sub-discipline of behavioural genetics devoted to environmental affects on the activation of genes involved in differences between people in their behaviour.
  Ie.: Experiences modify gene expression, potentially transgenerationally (e.g., smoking fathers affecting children’s eating habits) (Haig, 2007).
• Environmental Influences: Climate, diet, and social changes as selective pressures shaping adaptations.
• Adaptation vs. By-product: Distinguishes traits evolved for function from incidental outcomes.

Genes Are An Imperfect Recipe, Not A Blueprint

Genes are often described as blueprints for building the body, but a more accurate analogy is a recipe (Dawkins, 1982; Plomin, 2018).

Like baking a cake, the genetic code provides the instructions, while the environment—such as nutrition, upbringing, or social influences—acts like the oven’s temperature and ingredient quality, shaping the final outcome.

This explains why identical twins, despite sharing a genome, are never really quite identical in personality.

There’s no exact way to trace specific genes to specific traits, just as you can’t reverse-engineer cake crumbs into the recipe.

Still, researchers can estimate how much genes contribute to individual differences.

How to Explain Homosexuality

Research shows male androphilia is partly genetic and consistent across cultures (Alanko et al., 2010; Vasey et al., 2020), suggesting an evolutionary explanation is needed.

The question of why male same-sex attraction (androphilia) exists despite lowering direct reproduction has led to several evolutionary hypotheses.
Most focus on how such traits might still contribute to genetic fitness.

Four main hypotheses exist:

1. Kin Selection: Androphilic males may help raise relatives’ children, indirectly passing on shared genes.
   Evidence: Supported in non-Western cultures like Samoa and Indonesia (VanderLaan & Vasey, 2012; Nila et al., 2018), but less so in Western societies. Some scholars point out that Western societies are farther from our evolutionary past, so Samoans and Indonesians offer stronger evidence
2. Sexually Antagonistic Selection: SAS occurs when a gene boosts fitness in one sex but lowers it in the other. For male androphilia, the idea is that female relatives carrying the same X-linked genes may have higher fertility, but in males may be associated with same-sex attraction (Camperio-Ciani et al., 2004).
   Evidence: A number of studies appear to support this suggestion, including Camperio-Ciani et al. (2004) who found that mothers of androphilic men had an average of 2.7 babies whereas those of gynophilic men had an average of 2.3 babies
3. Heterozygote Advantage: Genes for androphilia might increase traits like empathy or sensitivity in heterosexual men, which are attractive to women and boost mating success (Zietsch, 2008).
   Evidence: Still speculative. ‘It has some support from the finding that ‘straight’ men who are better able to identify with women are sexually more successful (Zietsch, 2008)’.
4. Fraternal Birth Order Effect: The more older brothers a man has, the more likely he is to be androphilic, possibly due to biological maternal responses—seen as a variant of kin selection (Blanchard, 2018).
   Evidence: Replicated across cultures and studies (Blanchard, 2018). Each older brother increases the odds of male androphilia by ~30%. Likely a biological effect in the maternal womb (maternal immune hypothesis). Doesn’t explain all cases, but it’s robust, well-replicated, and measurable.

In conclusion, the evolutionary origins of male androphilia remain debated.
Theories may not be mutually exclusive, and a combination of mechanisms likely explains its persistence (Vasey et al., 2020).

3: Sexual Selection

Sexual selection, distinct from survival-focused natural selection, shapes traits enhancing mating success, explored through mate choice and competition in animals and humans.

Key Concepts

• Sexual selection: A type of natural selection where traits evolve because they increase mating success.
• Female choice: When females select mates based on preferred traits, driving the evolution of those traits.
• Parental investment: The time and energy a parent puts into raising offspring, affecting mating strategies.
• Handicap hypothesis: Suggests costly traits (e.g., a peacock’s tail) signal genetic fitness because only strong individuals can afford them.
• Parasite theory: Proposes that females choose mates with traits indicating resistance to parasites, promoting healthier offspring.
• Muller’s ratchet: The process by which genomes of asexual organisms accumulate harmful mutations over time.
• Tangled bank: A theory that sexual reproduction increases offspring diversity, helping them exploit different ecological niches.
• The Red Queen: Suggests species must continuously evolve to survive against ever-evolving parasites and competitors.
• Arms race: Escalating evolutionary competition between species or sexes (e.g., between predators and prey or between male and female strategies).

Theories of the evolutionary origin of male characteristics

The main theories are these, 🙋🏼‍♂️ put in nested order by me (Lucio):

• Fisher’s Runaway Selection (sexy sons): once a feature has been chosen by females it may become progressively exaggerated with each generation since females will constantly be looking for individuals with the largest, brightest example of that feature.
  The runaway may stop once it becomes too costly for survival and reaches an attract/survival optimum. Eg.: the peacock tail can’t grow larger (Zuk and Simmons, 2018).
• Parasite Theory (good genes): Mate choice reflects health and resistance to parasites. Brighter, healthier-looking mates likely have stronger immune systems (Hamilton & Zuk, 1982).
  That parasites kill more than predators may lend credibility to the parasite theory.
  • Red Queen Hypothesis (Van Valen, 1973): Related to parasite theories, it postulates that species must constantly evolve just to maintain their current fitness relative to co-evolving parasites, predators, or competitors — like running in place on a treadmill.
  • Zahavi’s Handicap Principle (costly/honest signaling): relates to the ‘god genes’ theory. Costly traits signal genetic fitness because only strong individuals can afford them. The “handicap” proves quality — it’s an honest, hard-to-fake signal (Zahavi, 1975).

Runaway/sexy sons VS Parasite theories/good genes have also been called ‘sexy sons’ versus ‘healthy offspring’.
Both sexy sons and healthy offspring can claim some support from the experimental literature

Studies show more parasites often correlate with more male ornamentation, backing the good-genes view.
But cases like swordtail and platyfish fish, where females prefer traits no longer present, support Fisher’s sensory bias idea.

Some traits may be both attractive and signal real fitness. For example, long swallow tails aid flight. Male–male competition may also play a role.

Examples like guppies, peacocks, and even potentially humans with testosterone show that natural and sexual selection may pull in different directions and males might have to make compromises.

In short, sexual selection is well supported, but its exact mechanism remains debated. Both theories (and sub-theories) are still in play and both may be valid.

Why We Have Sex: More Genetic Variation Means More Chances for Evolution

Although asexual reproduction is common and more efficient, sexual reproduction dominates in most multicellular species—despite its high costs.
These include:

• Losing half your genes in each offspring (“cost of meiosis”)
• Wasting resources on non-reproductive males
• Energy spent on courtship and mating (Maynard Smith, 1971; Williams, 1975)

Given these disadvantages, sex must offer a powerful evolutionary benefit to persist. The leading idea is that sex creates genetic variation, which helps species adapt to threats—especially from parasites, as proposed by the Red Queen hypothesis.

In short: sex is costly, but it persists because the genetic diversity it creates improves survival in a constantly changing and hostile environment.

We Have Sex As Protection Against Parasites: Red Queen Theory

The Red Queen theory (Van Valen, 1973) proposes that sex and sexual selection evolved as responses to the constant evolutionary arms race between hosts and fast-evolving parasites. Species need to constantly adapt just to maintain their fitness — “running to stay in the same place.”

This theory has gained strong support, especially through studies like Lively’s work on New Zealand snails, which showed that sexual reproduction is more common in environments with high parasite pressure (Lively, 1987; Lively et al., 1990; Morran et al., 2011). This suggests that sex provides genetic variation that helps offspring resist infections.

Although alternative ideas like competition between macro-organisms exist, current evidence favors the Red Queen’s focus on parasite-driven evolution, both for maintaining sex and possibly for shaping mate choice. Traits that signal parasite resistance may be key in what females look for in mates (Ridley, 1993).

Key Concepts

• Female choice shapes men: Female choice is a potent driver of evolution. ‘even in cases where males are much larger than females, female choice plays a role in reproduction‘.
• Intrasexual vs. Intersexual Selection: Competition within sexes vs. mate choice between sexes.
• Parental Investment Theory: The sex investing more (typically females) is choosier (Trivers, 1972).
• Homosexuality may be adaptive, maintained by selective pressures, especially in males (Vasey et al., 2020).
• Cryptic Female Choice & Sperm Competition: Females influence paternity post-copulation; sperm competes for fertilization.

💁🏼‍♂️ Lucio’s note: For more on sperm competition, we go deeper with both evidence and criticism in this review (also see ‘new sperm competition‘):

• Cambridge Handbook of Evolutionary Perspectives on Sexual Behavior

4: The Evolution of Human Mate Choice

This chapter applies sexual selection to human mate preferences and strategies, using cross-cultural and comparative studies.

Robust evidence supports sex differences rooted in evolutionary pressures, with cross-cultural data advancing understanding, though controversies (e.g., rape’s basis) persist (Walter et al., in press).

Key Concepts

• Sexual strategies theory: Proposes that men and women evolved different mating strategies based on differing reproductive challenges.
• Mate guarding: Behaviors intended to prevent a partner from cheating or being poached by rivals.
• Male provisioning hypothesis: Suggests that male investment in offspring (e.g. food, protection) evolved to increase reproductive success.
• Last common ancestor: The most recent species from which two or more current species descended.
• Male parental investment: The time, energy, or resources males devote to offspring, which can vary across species.
• Cryptic oestrus: Hidden ovulation in females, making it hard for males to detect peak fertility—thought to encourage long-term pair bonding.
• Sexual dimorphism: Physical differences between males and females of a species (e.g., size, coloration).
  Usually this means larger size for males. Polygynous mating systems (one male to a number of females) generally lead to a large degree of sexual dimorphism since males compete for ‘the prize’ of a number of female mates. In monogamous species, the sexes may be very similar in size since men don’t compete for females. Once paired up, it does not pay a male to compete for further females.
• Polygyny: A mating system where one male mates with multiple females.
• Polyandry: A mating system where one female mates with multiple males.
• Reproductive value: The expected future reproductive output of an individual, usually highest in young females.
• Sperm competition: Competition between sperm of different males to fertilize the same egg, often influencing male anatomy and behavior.
• Sexy sons: A hypothesis suggesting that females may choose attractive males so their sons will also be attractive and have high reproductive success.
• Coolidge effect: Males (and sometimes females) show renewed sexual interest when introduced to novel partners.

As seen above, humans can adopt any mating system.
Humans are plastic in their mating strategies, and vary depending on cultures:

Cross-cultural studies suggest that in reproductive matters we are a highly flexible species and that, unlike other species, our sexual strategy cannot easily be pigeonholed

Human Mate Preferences

• Long term: most of what both sexes want from a long-term partner is surprisingly similar.
  • Differences: As parental investment predicted (Trivers, 1972), men place greater emphasis on physical attractiveness and women place a premium on signals of wealth and status
  • Similarities: Both sexes require indicators of commitment and therefore, both men and women value love as of primary importance.
  • Women’s preference and variability: Yes, for long-term relationships women do want emotionally stable and dependable men who are well-off and of high status. But the relative importance of these features varies between cultures (Benton, 2000; Buss and Schmitt, 2019).
• Short term: the authors don’t delve as deeply into short-term preferences, but from what I know men to be more indiscriminate and ‘lower the bar’, while women may prefer sexier men and discount the importance of resources and provisioning

Although Buss’ original is not recent, the pattern of sex differences revealed in mate choice criteria has been replicated in more recent times, suggesting Buss’ findings are robust (Lippa, 2008; 2009, Walter et al., 2020;
see also Archer, 2019.)

Note: Rating scores potentially vary from 0.00 (irrelevant or unimportant) to 3.00 (indispensable).
Source: Adapted from Buss et al. (1990).

Women’s Attractiveness May Influence Her Promiscuity

Robert Trivers (1972) proposed that women adjust their sexual strategies based on their perceived attractiveness or “market value.”

According to this view, less attractive women may engage in more casual sex because they may anticipate lower chances of securing a high-investing long-term partner.

In contrast, those who perceive themselves as especially attractive are more likely to pursue high-status mates who offer greater investment (Trivers, 1972; Wright, 1994). <— 🙋🏼‍♂️ Lucio’s note: Since this is such a touchy yet important topic, I’d suggest removing Wright. As a journalist, he may not have been an original source

Empirical support includes Walsh (1993), who found that women who feel less attractive report having more partners, and studies showing that the most attractive women tend to pair with the most powerful men (Kanazawa & Kovar, 2004; Symons, 1979).

Women Choose Commitment or Promiscuity Based On Men’s Availability

Women’s mating strategies shift based on context.

Evolutionary psychologists such as David Buss (2011; 2016) and Symons (1979) argue that women adjust their reproductive behavior based on the availability of investing males, their own age and attractiveness, and their ability to secure resources independently

In environments where male investment is low—such as post-war tribal societies (Symons, 1979) or inner-city areas with high male unemployment (Buss, 2011; 2016)—women may adopt short-term mating to gain small benefits from multiple partners.

Evolution VS Culture: Eagly Criticism of Buss & Women’s Preferences

Across cultures, women prefer partners with financial resources more than men do.

However, the strength of this preference varies by culture. For example, women in India and Nigeria value financial prospects more than women in Sweden or the Netherlands.

This cultural variation led Alice Eagly and colleagues to propose a social role explanation: when women lack access to resources (e.g., through limited education or employment), they place more importance on a partner’s wealth.
Her research shows that women’s preference for male resources decreases as their own financial independence increases (Eagly & Wood, 1999).

Initially, this challenged evolutionary explanations.
But today, there’s general agreement—shared even by Eagly—that mate preferences are shaped by both evolved mechanisms and culture.
Evolutionary psychologists, including Buss, see human mate behavioural adaptations as structured to ‘respond contingently to local social and ecological factors’ (Kurzban and Haselton, 2006).

Also see:

• How Western social safety nets limit hypergamy

Major Insights

• Love is a universal human experience: Some thought of romantic love as a recent invention of Western culture (Symons, 1979; Jankowiak and Fischer, 1992), but evolutionary psychology destroyed this myth and it’s something that everybody can experience (see e.g. Jankowiak and Fischer, 1992; Toates, 2014)
• Male provisioning & ‘cryptic oestrus’ explains love: humans can’t be sure when women are fertile and many men invest in their women and children. This led to constant female sexual attraction which may well be a unique human feature and it may have led, in turn, to a unique long-lasting pair bond or, in colloquial language, ‘love’
• Female reproductive value VS fertility: Fertility refers to the likelihood of producing an offspring from a given mating whereas reproductive value is the potential for future offspring production.
  It’s an important distinction for men looking for either short-term sex, or long-term commitment. A 30-YO might be as fertile as 16-YO, but the 16-YO has higher reproductive value
• Sex Differences in Mating Strategies: Women favor resource providers, men youth/fertility cues, reflecting reproductive costs; pair bonds and male investment distinguish humans (Buss, 1994; Trivers, 1972).
• Sperm Competition, sexual dimorphism, & mating systems: Sexual dimorphism (different sizes between genders) and testes size indicate ancestral mating systems differences between chimpanzee (multiple mating, low sexual dimorphism, and sperm competition), gorillas (large sexual dimorphism, monopolization of females by the alpha, small tests and low sperm competition), and humans (in-between the two).
  Thus in males a large body size relative to females indicates polygyny (multiple mating partners for males) whereas large testes compared to closely related species indicates polygamy (multiple partners for both sexes)
• Short-term vs. Long-term Strategies: Dual strategies balance reproductive success (men) or resources (women) vs. stability (Baker & Bellis, 1990).
• Paternity Uncertainty and fidelity: Men focus on chastity and fidelity to ensure the child is theirs
• Coolidge Effect & Cryptic Oestrus: Male promiscuity and hidden female oestrus may reduce infanticide (Buss, 1989).

5: Cognitive Development and the Innateness Issue

Explores whether cognitive capacities are innate or learned.
A balanced view recognizes innate predispositions shaped by environment, with modularity accepted for basic functions, while neuroconstructivism, or development over time with experience, explains flexibility.

Key Concepts

• Nativism: The view that certain skills or knowledge are innate or biologically pre-programmed, similar to:
  • Modularity/innatism: The view that the mind is composed of distinct, specialized units (modules) evolved for specific functions.
    Ie.: the brain has pre-wired, specialized modules (like “language module” or “face recognition”) that are largely inborn and universal. Development mostly reveals what’s already built-in.
• Constructivism: The theory that development is an active process of building knowledge through interaction with the environment.
  Ie.: The brain starts more general and flexible, and builds specialized abilities over time through interaction with the environment and learning. Functions emerge, they’re not preloaded.
  Similar to:
  • Empiricism: The belief that knowledge comes primarily from sensory experience and learning.
• Epigenetic landscape: A metaphor for how gene expression is influenced by developmental pathways and environmental factors.
• Domain specificity: The idea that certain cognitive processes are specialized for particular types of information (e.g., language or faces).
• Imprinting: A rapid, early form of learning in which an animal forms attachments during a critical period (e.g., ducklings following the first moving object).
• Critical period: A fixed developmental window during which specific abilities must be acquired (or they never will be).
  • Sensitive period: A more flexible window during which learning is easier or more effective, but still possible later.
• Theory of mind: The ability to understand that others have thoughts, beliefs, and perspectives different from one’s own.
  Autism impairs theory of mind.
• Neuroconstructivism: The theory that cognitive development arises from dynamic interactions between brain development, experience, and environment.

Evolutionary Psychology Logic Supports Modularity

When a species repeatedly faces the same adaptive problem, natural selection would favor domain-specific mechanisms (i.e., modularity), because they’re more efficient than domain-general ones.

An evolutionary perspective would support modularity. Ie.: ‘A child who, at a young age, can communicate with others, recognise its family and show fear in dangerous situations will be more likely to survive than a child who develops these abilities much more slowly.‘

Important Concepts

• Core Knowledge Systems in infants: Infants show early grasp of objects, numbers, agents, suggesting innate modules (Pinker, 1994; Bushnell, 1982).
• Theory of Mind: Emerges around age 4, vital for social cognition, with variations in false belief understanding; impaired in autism (Baron-Cohen, 1995).
• Autism and Modularity: Autism may reflect impaired social modules, supporting modularity (Fodor, 1983).
• Prepared Learning for adaptive skills: Evolution primes learning of adaptive skills (e.g., snake phobias).

6: Social Development

Social development reflects evolutionary pressures for cooperation.
Life history and attachment theories are accepted, with ongoing social learning research.

Key Concepts

• Life history theory claims that, from an early age, children monitor their environment and make decisions about their future reproductive value and future strategies. Based on their assessment of the environmental conditions, they can choose to maximise current reproductive success or future reproductive success.
• Ontogenetic adaptations: Temporary traits in development that serve immediate adaptive functions (e.g., infant reflexes).
• Deferred adaptations: Traits expressed early that prepare for future benefits (e.g., play behavior for adult competence).
• Conditional adaptations: Traits that develop in response to environmental cues, adapting the individual to specific contexts.
• Attachment styles: Patterns of emotional bonding based on early caregiving, influencing later social and romantic behavior. Secure working models generally lead to more satisfactory and stable relationships in later life than insecure ones. Ainsworth proposed that there are three attachment styles, secure (Type B), insecure-avoidant (Type A) and insecure-anxious/resistant (Type C).
• C–F continuum (Cooperation–Fast continuum): A range from cooperative/slow life strategies to fast, opportunistic ones.
• Fast versus slow life history: Fast strategies involve early reproduction, impulsivity, and low investment; slow strategies involve delay, planning, and high parental investment.
• Principle of allocation: Organisms must trade off between competing demands (e.g., energy for growth vs. reproduction).
• Shared environment: Environmental factors that contribute to similarities between siblings (e.g., same household, parenting).
  • Non-shared environment: Unique experiences that make siblings different (e.g., different friends or teachers).
• Behavioural genetics: Studies genetic and environmental influences on behavior using methods like twin/adoption studies.
• Cooperation: Behavior where individuals work together toward shared goals, often benefiting group survival and success.
• Morality: Social rules and norms evolved to regulate behavior and promote group cohesion and cooperation.

Genes Effect the Environment

Genes and environment don’t act independently in shaping development.
Instead, genetic influences often shape the very environments people experience. B

ehavioral geneticists describe three main types of gene–environment interaction, showing that genes can help determine the kind of upbringing, treatment, and surroundings a person ends up with—meaning nature helps shape nurture:

• Passive interaction: Children inherit both their genes and much of their environment from parents. For example, intelligent parents provide both genes and a stimulating environment (e.g., books, conversation).

• Reactive–evocative interaction: A child’s traits (e.g., attractiveness) evoke different responses from others. Attractive children may be punished less or treated more positively, shaping their social experience.

• Active interaction: Children seek out environments that match their genetic dispositions—for instance, sporty kids gravitate to other active kids, and intellectually curious children look for stimulating peers or settings.

🙋🏼‍♂️ Lucio’s note: the other way around is also true
For example populations maintained enzymes to digest milk only after farming developed

The Evolution of Cooperation & Morality: We’re A ‘Morally Cooperative’ Species

Human cooperation extends far beyond kin-based altruism, involving shared goals, coordination, and cultural norms that enable large-scale collaboration—even among strangers.

From infancy, humans demonstrate proto-conversational turn-taking and shared attention, which form the foundation for coordinated efforts.
Unlike chimpanzees, young children actively re-engage partners, prefer collaboration even when solo work is easier, and develop, critique, and enforce norms—behaviors rooted in an early-emerging sense of collective “we.”

For a long time, it was thought that morality contradicted the principles of evolutionary theory.
But morality may have developed alongside win-win cooperation.

Models of Morality

• Fiske’s model defines morality through relationship types, with norms evolving to support cooperation (Rai & Fiske, 2011):
  • Community sharing (kin and group cohesion)
  • Authority ranking (hierarchy)
  • Equality matching (reciprocity)
• Curry’s game-theoretic model adapts social dilemmas (e.g., hawk-dove, mutualism, exchange, contests, division) to show how moral rules resolve conflicts and distinguish between kin-based and non-kin cooperation.
  See the table:

Both models have more in common than they differ.
Fiske underplays the differences between kin and non-kin interaction, and Curry underplays the hierarchical structure of human societies.
Both agree that morality evolved to enable humans to cooperate at large scales, employing norms to offset our innate selfish tendencies.

Key Points

• Cooperation is strongly linked to morality. In fact, morality is one of the forces that drives us to cooperate. The reason why people cooperate fairly is either because they feel bad if they don’t or because they fear being punished if they are caught cheating.
• Children are born wired for social interaction and quickly develop the motivation and skills to share their experiences and their goals with others. Unlike chimpanzees, which prefer to act alone unless it is impossible to do so (such as a hunt) children prefer to cooperate with others, even when it is not strictly necessary
• Attachment Theory: Early bonds (secure/insecure) affect adult relationships (Bowlby, 1969).
• Life History Theory: Life history applied to attachment theory suggests that attachment style may be adaptations. Early environments shape fast (risk-taking) vs. slow (investment) strategies (Belsky et al., 1991; Chisholm, 1993).
  • Parents provide environmental cues: Life history theory suggests that genes build mechanisms that enable children to use their parents’ behaviour as a way of choosing (unconsciously) a reproductive strategy. For example, an absent father may cue children to promiscuity and early reproduction, while a stable and doting family may predispose for stable relationships
• Twin studies help us estimate the impact of nature VS nurture: the amount of variation between individuals can be calculated by looking at the differences between identical twins reared apart on the trait because, since they are genetically identical, it follows that any difference between them must be due to the environment. The results of such studies estimate that the environment accounts for between 50-60% of the variation among them on a variety of traits and genes for 40–50%.
  • Genes may be under-estimated because genes have a secondary effect on life experiences. For example, attractive people are generally more assertive, a finding that is explained by the observation that attractive people are generally treated with more deference (Jackson and Huston, 1975)
  • Genes may also be underestimated 2 (Conditional adaptation theory): because instead of pre-programming everything, they equip us with modules for adapting to the environment.
    See below
• Shared environment matters little: Behavioural genetics research using twin and adoption studies suggest that not only do all traits have a degree of heritability (often around 50 per cent), but the remaining variation in traits is accountable to the non-shared rather than the shared environment (ie.: parents don’t seem to make a large difference)

7: Kin Relationships and Conflict

Explains family altruism and conflict via inclusive fitness, focusing on kin dynamics.

Kin behaviors are central, with strong evidence for inclusive fitness and conflict; grandmother hypothesis and Cinderella Effect are supported, though culture plays a role.

Key Concepts

• Inclusive fitness: Total genetic success from one’s own reproduction (direct fitness) plus helping relatives reproduce (indirect fitness).
  Inclusive fitness explains kin altruism

• Direct and indirect fitness:
  • Direct: Offspring produced by the individual.
  • Indirect: Extra offspring produced by relatives due to the individual’s help.

• Coefficient of relatedness (r):
  Probability that two individuals share a gene from a common ancestor (e.g., r = 0.5 for siblings or parent-child).

• Kin altruism (AKA nepotism):
  Helping relatives reproduce, even at a cost to oneself, because shared genes benefit (explains altruistic behavior toward kin). The tendency to provide aid to relatives appears to be related to the proportion of genes shared by common descent (i.e. the coefficient of relatedness – ‘r’).

• Parental investment:
  Time, energy, and resources parents invest to increase offspring survival and future reproduction.
  In some species a large number of offspring are produced but very few resources are provided for each (‘r-selection’). In others, a great deal of effort is spent on each of a small number of offspring (‘K-selection’).
  • Life history: the context of human life history theory, these are also known as ‘fast’ and ‘slow’ selection. With important exceptions, humans and other primates are at the extreme end of K-selection (fewer children, high investment)

• K- and r-selection:
  • K-selection: Fewer offspring, high investment (e.g., humans).
  • r-selection: Many offspring, low investment (e.g., insects).

• Parent–offspring conflict:
  Evolutionary conflict: offspring want more resources than parents are selected to give (due to parents’ need to divide resources across multiple offspring).
  • Parental manipulation: Parents influence offspring behavior to maximize their own inclusive fitness (may not always align with offspring’s best interests).

• Grandmother hypothesis: Post-menopausal women increase their inclusive fitness by helping raise grandchildren rather than having more children themselves.
  • Grandmothers VS grandfathers: Due to the possibility of non-paternity, paternal grandparents are predicted to provide a lower level of investment than maternal grandparents.

Key Concepts

• Hamilton’s Rule: rB > C drives kin altruism (Hamilton, 1964).
  Meaning: helping relatives (kin altruism) evolves when the genetic relatedness (r) times the benefit to the relative (B) is greater than the cost to the helper (C).
• Kin altruism boosts inclusive fitness
• Poor parents under-invest in unhealthy offspring when wealthy parents had children with medical and psychological problems they increased their investment, whereas poor parents provided the least parental care to the least healthy offspring (Bugental et al., 2013; Pelham, 2019).
• Places with high infant mortality may lead to lower care: A study of 150 nations found that countries with high parasite load and high infant mortality parents tend to invest less in each offspring and to encourage child labour (Pelham, 2019)
• Parental Investment and Conflict: Sibling rivalry and weaning conflicts arise from differing optima (Trivers, 1974).
  • Parents may manipulate into more cooperation: Alexander (1974) suggests parents might increase their inclusive fitness by teaching appropriate moral code. In particular, parents tend to teach their children to behave benevolently towards each other
  • Mother-child interest conflict after one year when the mother may want to have another child, but the child may want to monopolize investment
  • Mother-daughter interest may conflict if the daughter has a child too soon when the mother is still of child-bearing age
• Grandmother Hypothesis: Menopause aids grandchildren’s survival (Hawkes, 1998).
• Kin Recognition: Mechanisms (e.g., MHC genes, familiarity) support altruism (VanderLaan et al., 2012).
• Cinderella Effect: Stepparents’ higher abuse rates reflect lower genetic investment (Daly & Wilson, 1988).

8: Reciprocity and Conflict Among Non-Kin

Focuses on non-kin cooperation and conflict, including reciprocal altruism and violence.
Reciprocal altruism underpins cooperation, supported by game theory and ethnography; conflict (e.g., Dark Triad, violence) is studied, with ethical debates ongoing.

Key Concepts

• Reciprocal altruism – direct reciprocation: Helping others with the expectation they’ll help back in the future; a “you scratch my back, I’ll scratch yours” dynamic.
  Direct reciprocation consists of self-sacrificing acts between two unrelated individuals that are based on delayed reciprocation
  • Rare in animals foundational in humans: some evolutionary psychologists consider reciprocation a foundational stone of human social behaviour.
• Xenophobia: Fear or distrust of outsiders or strangers, possibly evolved as a protective mechanism against unknown threats.
• Gift economy: A system where goods/services are given without explicit agreements for immediate or future returns, building social bonds and status.
• Game theory: A mathematical framework to study strategic interactions between individuals, it has been used by evolutionists to model the behaviour of humans and other species under simplified versions of social decision-making scenarios
  • Prisoner’s dilemma: A game theory scenario where mutual cooperation is best long-term, but individuals are tempted to defect for short-term gain. Tit-for-tat was the most effective strategy:
  • Tit-for-tat: A simple and effective strategy in repeated games—start with cooperation, then match the partner’s previous move in the next encounter (cooperate with cooperators or defect with defectors).
    It’s an evolutionarily stable strategy (ESS), and humans develop it when playing repeated prisoner’s dilemmas. It suggests that we seek cooperation but bear grudges when cooperation is not reciprocated.
• Evolutionarily stable strategy: A strategy that, if adopted by most of the population, cannot be beaten by an alternative strategy.
• Stereotyping: Overgeneralized beliefs about members of a group; may have evolved as a cognitive shortcut for social prediction.
• Ethnocentrism: Viewing one’s own group as superior and using it as the standard to judge others; possibly evolved to promote group cohesion.
• Dark Triad: A cluster of three personality traits—Machiavellianism, narcissism, and psychopathy—associated with manipulation, callousness, and self-interest.

Prerequisites for reciprocal altruism

According to Trivers, reciprocal altruism requires:

1. Reasonably long lifespan to repeatedly encounter specific individuals and thereby allow for reciprocation to occur
2. Cost/benefit arbitrage: cost of altruism for the recipient should be lower than the benefit to the recipient
   🙋🏼‍♂️ Lucio’s note: I don’t see why this should be a strict requirement, since your cost of giving can be higher than the benefit of the recipient, but still pay off if the recipient’s repayment outweighs your cost
3. Ability to recognise each other in order to both reciprocate and to detect cheats (non-reciprocators).

Freeriders threaten cooperation: remove them to keep a good-functioning group

Cooperation among non-kin is threatened by freeriders — individuals who benefit without contributing.

According to Tooby et al. (2006), cooperation could not have evolved unless mechanisms emerged to detect and manage freeriders. Once detected, two main responses are available: punishment (Price et al., 2002) and withdrawal of cooperation.

In public goods games, where individuals contribute to a shared pool that benefits all, cooperation starts high but declines as freeriding increases. A meta-analysis by Fehr and Schmidt (1999) found that contributions dropped from 40% to nearly zero across rounds, with 73% of participants making no contribution by the final round. Participants reported that freeriding by others led them to stop cooperating.

Allowing participants to punish freeriders drastically improves cooperation. When fines could be used, only 20% failed to cooperate in the final round (Fehr and Gächter, 2002). Real-world parallels appear in common-pool resource systems, where Ostrom (1990) found that all successful common-pool resources share effective monitoring and punishment systems. Punishment — or the credible threat of it — is therefore crucial to maintaining cooperation (Fehr and Gächter, 2000).

The greatest cost that freeriders inflict is the loss of all the potential gains from n-party exchanges that otherwise would have been achieved if freeriding had not triggered antiexploitation motivational defenses among cooperators (Tooby et al., 2006)

Xenophobia may be adaptive

Xenophobia may be adaptive, and also help explain why many can be so easily indoctrinated into populism and nationalist ideologies.

Xenophobia may have developed with:

• ‘Cheat detection’ mechanisms: If ancestral human societies were largely based around acts of kin altruism and reciprocation, then selective pressures would also have led to the evolution of psychological mechanisms to spot cheats and to be suspicious of strangers until we are reassured that they are not freeriders
• Ingroup/outgroup: the formation of a group identity can lead to positive in-group and negative out-group stereotyping.
  Our own view of ourselves – our self-concept – may also be constructed partly out of group memberships, so we tend to view our own groups as positive (Bierhoff, 1996)
• Coalitionary aggression: Some have controversially stated that xenophobia help form coalitions and it may have been an adaptive strategy

In Sherif’s famous experiment, children divided into two groups readily formed started behaving gang-like towards the other, and only the introduction of an imaginary third group relieved the hostility (Sherif, 1956).
Sherif’s experiment teaches us that to stop inter-group conflict a common enemy is the solution to remove hostility and foster cooperation.

Tajfel’s subsequent studies suggest that we don’t have to seek out like-minded compatriots, we just have to have something (anything) that allows us to feel part of a group and then discriminate in favour of some individuals on the basis of arbitrary and anonymous group membership alone (Tajfel, 1970).

It seems that people will latch on to almost any cue to distinguish in-group and out-group members (John Archer, 1996)

Key Concepts

• Direct and Indirect Reciprocity: Tit-for-tat and reputation-based cooperation (e.g., !Kung San food sharing) (Trivers, 1971; Lee, 1968).
• Costly Signalling Theory: Prosocial displays boost status.
• Machiavellian Intelligence: Social manipulation drove brain evolution (Zeigler-Hill et al., 2016).
• Jealousy gender differences: Sex differences tied to infidelity concerns (Buss et al., 1992).
• Dark Triad may be adaptive in some contexts (Zeigler-Hill et al., 2016).
• Freeriders: Threaten cooperation, countered by cheater detection (Cosmides & Tooby, 1992).

9: Evolution, Thought and Cognition

Examines how evolution shaped reasoning, memory, and decision-making, emphasizing how an evolutionary approach can better help us understand why the mind works the way it does (ie.: focus on what it was designed to do).

Cognitive processes are ancestral adaptations; modularity and adaptive memory are accepted, with debates on domain-specific vs. general mechanisms.

Key Concepts

• Computational theory of mind – The mind is like a computer: it processes information through symbols and rules. Evolutionarily, it suggests natural selection shaped the brain to solve adaptive problems via mental computations.
• Substrate neutrality – The idea that computation doesn’t depend on the material doing it (brain, silicon, etc.). Evolutionary relevance: mental adaptations can be understood in terms of function, not biology alone.
• Episodic and semantic memory – Episodic: memory of personal events; Semantic: general knowledge and facts.
  Evolution: episodic memory helps track social and environmental events; semantic memory aids in survival through stored knowledge.
• Cognitive economy – Mental efficiency: organizing information in a way that reduces processing effort. Evolutionarily adaptive for conserving energy and making fast decisions.
• Typicality effect – Some category members (e.g. robin as a bird) are judged faster/more “typical” than others (e.g. penguin).
  Evolution: may reflect prototype-based categorization that speeds up recognition and action.
• Indicative and deontic reasoning – Indicative: reasoning about what is true (logic/facts); Deontic: reasoning about what one should do (rules/obligations). E
  volution: deontic reasoning likely evolved to navigate social norms and cooperation.
• The gambler’s fallacy – Mistaken belief that past random events affect future ones (e.g., “red hasn’t come up, so it must now”).
  Evolution: may stem from evolved pattern-detection mechanisms misfiring in modern settings.
• The hot hand fallacy – Belief that someone on a winning streak is more likely to continue succeeding. Evolution: possibly linked to tracking social status or skill, which may have been adaptive in group dynamics.
• Foraging theory – Models how animals (including humans) search for and exploit resources efficiently, and since in nature streaks or patterns can mean something (e.g., a fruitful berry bush or a good hunting ground), our minds may have evolved to expect non-randomness.
  • Marginal value theorem – A principle in foraging theory stating when an animal should leave a resource patch: when the rate of resource gain falls below the average elsewhere. Applied to mate choice, information seeking, etc.

Main Ideas

• Wason Selection Tasks: Humans excel at social contract logic (Wason, 1966).
• Visual Illusions Aren’t Illusions But Features: Adaptive “errors” (e.g., shadow illusion, “The Dress”) reflect survival-tuned perception (Adelson, 1995).
  Our visual systems did not evolve to present us with a true description of the world, but to provide a useful description of the world that supports our actions upon it.
• Intelligence evolved to help us survive and reproduce: Evolved via social, ecological, and sexual pressures; practical intelligence often undervalued.
• Adaptive Memory: Prioritizes survival info (e.g., predators) (Nairne & Pandeirada, 2008).

11: The Evolution of Emotion

Emotions are universal adaptations modulated by culture, supported by functional and neuroimaging evidence.
The authors present emotions as evolved response systems aiding survival and reproduction.

Key Topics

• Basic Emotions: Universal (e.g., anger, fear) with physiological/cognitive bases (Ekman, 1992).
  • Smile as appeasement: van Hooff sees two dimensions in pro-social gestures – ‘friendliness’ (smiling) and ‘playfulness’ (laughing).
    In this way smiling and laughter form a continuum with two dimensions. The silent bared-teeth display originated as an appeasing signal and later evolved into a friendly gesture.
• Display rules modulate the ‘appropriateness’ of emotional expression within a certain culture.
  People still generally feel the same emotions, but the outward display may vary
• What’s attractive varies by culture: There is a great deal of scope for modification during development. In some cultures, for example, scars or tattoos are attractive while they’re ugly disfigurements in others (Carlson et al., 2000).
  Cultures can also change rapidly.
• Jealousy and Sexual Strategies: Males focus on sexual infidelity, females on emotional (Buss et al., 1992).
• Plutchik’s Wheel: Eight primary emotions, opposites, and combinations.
• Functional Roles of emotions: Fear avoids danger, disgust prevents contamination, joy boosts cooperation (Nesse, 1990; Fredrickson, 2001).
• Some negative emotions may not be adaptive, but a cost to pay for their positive expression: Bereavement may serve no adaptive function but the price we pay for love and attachment, similar to drug withdrawal.
  Determining which emotional states are adaptations and which are emergent properties will be a difficult task for researchers

12: Evolutionary Psychopathology and Darwinian Medicine

Applies evolution to mental disorders and health, viewing them as exaggerated or mismatched traits.
Evolutionary psychopathology explains disorder persistence; Darwinian medicine gains traction, with depression and schizophrenia models debated but accepted, requiring ethical care.

The evolutionary logic of pathogen virulence

The virulence of a disease depends on how and how fast it’s transmitted, and when it affects the recipients.

Paul Ewald proposed that pathogens spread through direct contact (like the common cold) tend to be less harmful, since keeping the host active helps transmission.

In contrast, those spread by vectors (like mosquitoes in malaria) can afford to debilitate or even kill the host, as transmission doesn’t rely on the host’s mobility.

To put it crudely, killing the host may not matter as long as there are plenty of opportunities for the vector to take copies of the pathogen onto other hosts (Nesse and Dawkins, 2010).

Harmful genes may also be maintained in our species if the harmful gene has its effects after the age of reproduction.
Then, natural selection is unable to remove it from a population. In this way inherited diseases such as Huntington’s chorea, which does not emerge until middle age, may be kept in the population.

Heterozygous advantage: sickle cell example

Some harmful genes are preserved in human populations because they provide benefits in certain genetic combinations.

A classic case is sickle-cell anaemia: having two copies of the gene causes illness, but having just one (heterozygous) provides resistance to malaria, offering a survival advantage in malaria-prone regions. This phenomenon is known as heterozygous advantage—when carrying two different alleles leads to greater fitness than having either allele alone.

This dynamics is similar to the ‘sexually antagonistic selection’ we saw earlier:

Heterozygous Advantage VS Sexually Antagonistic Selection

They’re different concepts, but both explain how seemingly disadvantageous genes can persist in a population.

• Heterozygous advantage is about genotype combinations (allele pairing).
  Mechanism: Maintains genetic variation because the intermediate genotype is the fittest.
• Sexually antagonistic selection is about sex-based fitness tradeoffs.
  Mechanism: Maintains genetic variation because it benefits one sex while hurting the other.
  One theory explaining homosexuality was based on sexually antagonistic selection: it may help women be more fecund, but it costs to some men.

Depression = low status; Machs = high status

Research on vervet monkeys and humans suggests that serotonin levels are closely tied to social status and may play a role in depression.

In monkeys, alpha males had serotonin levels twice as high as subordinates, but when they lost their dominant position, serotonin dropped sharply, and their behavior changed—becoming withdrawn, rocking, and refusing to eat, similar to symptoms of depression in humans (Raleigh and McGuire, 1991; McGuire et al., 1997).

When treated with Prozac (an SSRI), these symptoms disappeared, and monkeys given Prozac became alpha males when the original one was removed (McGuire et al., 1997; McGuire and Troisi, 1998).

In humans, some studies classify males as either ‘Machiavellians,’ who are relatively aggressive and competitive, or ‘moralists,’ who are more deferential.
🙋🏼‍♂️ Lucio’s note: I find the researchers’ choice of name to be sub-optimal. ‘Dominant men’ would have been a better fit than ‘Machiavellians’.

For Machiavellians, social rank and serotonin levels are positively correlated, while for moralists the relationship is negative (Madsen, 1985; Madsen and McGuire, 1984).

This suggests that, like vervet monkeys, high-status pushy males tend to have higher serotonin.

Since low serotonin is linked to depression (Ray, 2018), these findings provide indirect support for Price’s social competition hypothesis, which proposes that low mood can be an adaptive response to failure in gaining status.

While this hypothesis might be criticized for focusing on male-typical competition, women also compete for status in less overt ways (Cashdan, 1996; Campbell, 2002; 2006; 2020). If supported, the social competition hypothesis could help Darwinian medicine guide clinicians in identifying and understanding some forms of depression.

Also read:

• How to become more positively Machiavellian

The evolutionary reason for psychopathy: leeching off of cooperators

Psychopathy, often considered synonymous with antisocial personality disorder (APD), is characterized by a lack of empathy, callous exploitation of others without guilt, low anxiety, and a preference for immediate gratification.

Evolutionary psychologists propose that psychopathy may represent an adaptive “cheater” strategy that takes advantage of the widespread reciprocal cooperation in human populations.

Such an argument for persons with APD has been considered by a number of evolutionists (Mealey, 1995; 2005; McGuire et al., 1997; Glenn et al., 2011) but is particularly associated with McGuire and Troisi (1998).

For such a strategy to persist, two key conditions must be met:

1. there must be a genetic basis for psychopathy
2. most individuals in the population must be cooperators or reciprocators

Empirical evidence supports these conditions, with studies showing higher concordance rates for APD in monozygotic twins compared to dizygotic twins, increased incidence in adopted children of biological parents with the disorder, and a five-fold increased risk among first-degree male relatives.

Psychopathy affects approximately 3% of adult males and 1% of females, with its higher prevalence in males potentially explained by stronger migratory tendencies that reduce detection.

Moreover, around half of psychopaths may remain undiagnosed, suggesting that this freeriding strategy can be effective and enduring within human populations.

Balancing and Shifting Theories of Psychopaths

Balancing and shifting theories build on the idea of psychopathy as an evolved cheating strategy by focusing on how genetic predispositions interact with environmental conditions to influence the development and expression of psychopathic traits.

The balancing theory proposes that certain genes create a vulnerability (diathesis) to psychopathy, which may be expressed depending on social environments—such as densely populated cities where exploitation is more advantageous, versus smaller, more intimate communities where such behavior is less successful. This view supports a bio-social interactionist model where the environment triggers genetic potential.

🙋🏼‍♂️ Lucio’s note: modern societies must be careful
This suggests that advanced societies’ urbanization may increase the incidence of psychopathy.

The contingent shift theory suggests that all individuals possess modules that, when triggered by adverse environments (e.g., childhood abuse), can produce psychopathic traits.
Unlike the balancing theory, which sees only a minority genetically predisposed, this theory argues that psychopathy could potentially develop in anyone under the right conditions.

🙋🏼‍♂️ Lucio’s note: The prevalence hypothesis, also known as frequency-dependent selection, was missing in the paragraph but explained later.
It proposes that psychopathy can be an adaptive strategy only if psychopaths remain a small minority in the population. If too many individuals behaved this way, social cooperation and reciprocity would break down, making the strategy ineffective. Thus, natural selection maintains psychopathy at low but stable levels—around 1–3%—allowing it to persist as a successful “cheating” strategy without undermining social order.

Evidence linking psychopathy to evolved strategies is suggestive but not definitive, partly due to disagreements over genetic-environment interactions and the proportion of the population affected. Factors like high conflict and low parental warmth are correlated with psychopathy but don’t conclusively prove it’s an evolved adaptation.

Complicating the picture, Linda Mealey proposed two types of psychopathy: one largely genetic and independent of environment, and another emerging from perceived social disadvantage.
Additionally, psychopathy’s role within the “Dark Triad” personality cluster alongside Machiavellianism and narcissism supports its adaptive function in some contexts.

Given its widespread cross-cultural presence, evolutionary explanations remain essential to fully understanding psychopathy, even as the details continue to be debated.

🙋🏼‍♂️ Lucio’s summary:

• Psychopathy is biological: Recent neurobiological studies highlight differences in brain structure/function in psychopaths (e.g., amygdala, prefrontal cortex), suggesting a biological basis.
  • Environment plays a role, but it’s debated how much/in which circumstances
• Psychopathy likely has an adaptive basis but only in specific social and environmental contexts. Many researchers consider at least some aspects of psychopathy to be adaptive in evolutionary terms, especially in certain social environments. Psychopathy may confer reproductive or social advantages through manipulative, risk-taking, and exploitative behavior.
  • However, it is not adaptive in all contexts and carries costs that limit its prevalence.
• The balancing theory is the most widely supported framework, incorporating both genetic predisposition and environment
  🙋🏼‍♂️ Lucio’s note: this seems to be the same as ‘weather forecasting’/’conditional adaptation theory’
• The prevalence hypothesis—that psychopathy remains rare because it only works as an adaptive strategy when few individuals have it—is well supported and largely accepted.
• The contingent shift theory is less supported due to difficulties explaining prevalence and genetics.

Future research will likely refine these models, possibly supporting a nuanced view with multiple psychopathy subtypes and complex gene-environment dynamics.

Also see our investigation on a psychopath’s worringly methodical fast-life strategy to reproduction:

• Psychopath’s fast life sexual strategy

Life history approach to psychopathology

Marco Del Giudice’s Fast-Slow-Defence (FSD) model is a new evolutionary framework for classifying psychopathology based on life history theory.

It categorizes disorders into three spectra:

• Fast spectrum (F-type): Linked to early, impulsive life strategies, associated with disorders like impulsivity and antisocial behavior.
• Slow spectrum (S-type): Linked to slower, more controlled life strategies, associated with overly controlled behavioral problems.
• Defence activation (D-type): Disorders arising from overactive self-protective emotional responses like anxiety, fear, and shame (e.g., social anxiety, eating disorders), overlapping with both F- and S-types.

The model challenges the traditional DSM approach by focusing on underlying adaptive functions and developmental dysregulation rather than symptom clusters. Though promising, it is still new and awaits further validation.

Why psychiatric problems persist

Evolution hasn’t eliminated psychiatric problems because it’s not designed to produce perfect mental health. Instead, it optimizes for reproductive success.
Randolph Nesse (2019) outlined six evolutionary reasons why psychological disorders persist:

1. Trade-offs (Pleiotropy): Some traits or genes have both benefits and costs; for example, the same trait that enhances creativity might also increase risk of mood disorders.
2. Mismatch Hypothesis: Our brains evolved for ancestral environments, and many modern stressors (e.g., social media, urban isolation) are evolutionarily novel.
3. Trait Variation Argument: Traits vary across a normal distribution, and while the law of optimum balance says that within a range many traits are adaptive, some people will naturally fall at maladaptive extremes (e.g., some anxiety is good to keep you alive, but a minority of people will naturally inherit very high anxiety, which is detrimental).
4. A) Reproduction Over Health (compromise argument): Natural selection favors traits that boost reproduction and inclusive fitness, even if they harm long-term health or mental stability.
   • B) Exaggerated But Defensive Responses (compromise argument): Pain, anxiety, and depression may be exaggerated but adaptive responses to real or perceived threats.
   • Examples: Having children can be very taxing on a woman’s health and having high levels of testosterone is useful in young men, but it also puts a strain on a man’s body, which is one reason why women, on average, live longer than men. But they both persist for the advantages they confer
5. Evolving Pathogens: Pathogens evolve faster than humans; while mostly relevant to physical illness, some brain infections or immune responses can contribute to mental disorders

Concepts

• The symptoms caused by microbial parasites are adaptations either of the pathogen to aid its multiplication or of the host to kill off or expel it.
  Understanding which symptoms are designed to destroy the pathogen or to spread it might inform treatment
• Evolutionary arms race of parasite VS host: The relationship between host and parasite has been portrayed as an evolutionary arms race of adaptation and counter-adaptation (Red Queen)
• Mismatch Theory: Modern conditions mismatch ancestral adaptations (e.g., obesity) (Nesse & Williams, 1994).
  Other explanations:
  • Genes that cause illness might also have positive facets associated with them – the pleiotropy argument;
  • Selection pressures act on increasing inclusive fitness, not on perfecting systems – the compromise argument;
  • Disorders might be viewed as the extremes of normal variation – the trait variation argument.
• ‘Smoke detector principle’ of anxiety: it pays off to be anxious. The costs of being a little too anxious may well have been small when compared to the costs of not being sufficiently anxious
• Symptoms as Adaptations: Fever, pain as defenses.
• Infectious Diseases: Co-evolutionary arms race with pathogens.
• Genetic Conditions: Sickle cell aids malaria resistance.
• Blue Eyes and SAD: Possible resilience link (Workman et al., 2018).
• Smoke Detector Principle: Anxiety as overactive defense (Nesse, 1998).

13: Evolution and Individual Differences

Explores why traits like intelligence and personality vary, despite natural selection.

Summary of the different accounts of individual variation depending on its source (heritable vs environmental) and its effect (adaptive, non-adaptive, maladaptive)

Innate ≠ genetic, because genes can’t code everything

This was an aha-moment for me:

The brain is incredibly complex, with billions of neurons and trillions of connections. Our genes don’t contain enough instructions to fully specify everything in this detailed wiring.
Even identical twins, who share the same DNA, have noticeable differences in their brains and personalities from birth.

These differences can’t all be explained by environment or upbringing either—some seem to come down to random chance. Tiny events during development—like a neuron growing slightly differently, or a random mutation—can lead to variations in the brain’s structure and function.

This kind of variation isn’t shaped by evolution or adaptation; it’s non-adaptive. It happens simply because building a brain (or body) from limited genetic instructions leaves room for randomness.

🙋🏼‍♂️ Lucio’s note: brain structure and personality is innate, but not everything that is innate is genetic
This also means that some differences between people are innate in the sense that they arise during development (before birth or early in life), but they are not genetic because they’re not directly caused by differences in DNA.

Key Ideas

• Personality: From an evolutionary point of view we might think of personality as a behavioural strategy. Some people, for example, gain access to resources by dominating others, whereas others do it by being deferential
  • Traits: Personality tests usually measure ‘traits’ (or sometimes ‘factors’; see later) – that is, enduring facets of a personality such as how ‘outgoing’ or ‘liberal’ a person is rather than states (Schultz and Schultz, 2005; Haslam et al., 2017).

One possible account for the variation (of) personality is that some phenotypes might profit in certain conditions and others in quite different conditions.
For example, speculatively, hard times might favour individuals who are likely to cooperate – there is a need to work together – whereas good times might favour individuals who are more selfish – since there is plenty for all.

• Morally positive/negative traits may be unrelated to fitness: Traits or factors that seem negative in some moral sense might well have positive effects on fitness.
  Eg.: agreeable people and trusting people may be more easily exploited, whereas cynical people might avoid cooperation in the face of freeriders
• Many genes regulate most personality traits: many aspects of individual differences such as personality and intelligence are likely to be highly polygenic (i.e. they depend on many genes, potentially thousands; Heck et al., 2009; Plomin, 2018)
  Differences in the big five between people are due, not to a small number of genes having a large effect, but to a very large number, each of which has a tiny effect (Sanchez-Roige et al., 2018; Plomin, 2018; Flint, Greenspan and Kendler, 2020)
• Heritability: Personality (30–50%), intelligence (up to 75%) (Turkheimer, 2000).
  • Genetic heritability may be higher than 30-50%: Early environmental calibration theory suggests that the non-heritable portion of personality may at least partly be explained by evolved, environmentally contingent cognitive and emotional mechanisms that sample the world and affect the phenotype based upon a best-guess prediction of the future.
    The environment matters, but rather than ‘pounding us into shape’, it selects a phenotype from a battery of alternatives (Myers and Bjorklund, 2020).
• ‘Weather forecasting’ and early environmental calibration theory (Myers and Bjorklund, 2020): Personality may only be partly genetically specified natural selection cannot entirely specify a successful phenotype for all different environments. So genes specify psychological mechanisms that are capable of tuning or calibrating a personality that better fits the environment in which an individual develops
  • Secondary psychopathy may develop with environmental interaction and gene–environment interaction. Unlike primary psychopaths, largely genetic and fixed, secondary psychopaths inherit a predisposition that may only express under growing up in harsh environments, densely populated areas, or places where cheating is easier and less likely to be detected. This makes secondary psychopathy a conditional adaptation shaped by early-life experiences (Mealey, 1995).
• Niche-Fitting Hypothesis: Specialization based on ecological demands.
• Intelligence helps survival and reproduction
  • Definition: [I]ntelligence is the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience (Plomin, 2018)
  • General VS specific: there is a long-standing debate as to whether there is a single underlying general intelligence (g), several multiple intelligences or some combination of both of these
  • Intelligence and niche-fitting: for those who adhere to the multiple intelligences view, variation in intelligence can be explained by ‘niche fitting’, specializing in spatial tasks, linguistic tasks, or understanding people
  • Sexual Selection for Intelligence: Signals good genes.

14: Evolutionary Psychology and Culture

The authors examine culture-evolution interplay, viewing humans as cultural animals.
An integrated biology-culture view is advocated; gene-culture coevolution is accepted.

Key Concepts:

• Superorganic: Culture exists above individuals as a system with its own dynamics (general);
  Evolutionary: sees this as misleading, favoring individual-level evolved mechanisms instead.
• Cultural Transmission: The passing of cultural traits between people or generations (general);
  Evolutionary: studies the evolved learning biases that make transmission possible and efficient.
• Evoked VS Transmitted Culture:
  • Evoked culture: Cultural differences that arise from universal psychological mechanisms responding to different environments (e.g.: recall fast and slow life histories)
  • Transmitted Culture: Traits passed down through imitation or teaching, regardless of environment (general);
    Evolutionary psychology sees this as shaped by evolved preferences for social learning.
• Dual-Inheritance Theory: Humans inherit both genetic and cultural information;
  Evolutionary: partially overlaps, but tends to focus more on gene-driven mechanisms than cultural evolution per se.
• Gene–Culture Co-evolution: Genes and culture influence each other’s evolution (general);
  Evolutionary: uses this to explain traits like language or lactose tolerance evolving from cultural practices.
• Memes and Memetics: Ideas or behaviors that replicate and spread like genes (general);
  Evolutionary: is cautious, viewing memes as illustrative but often lacking explanatory power.
  • Culturegens: Hypothetical units of cultural information;
• Imitation and humans’ superior imitation: The chapter opens highlighting how a human child imitated to a much larger degree than a chimpanzee (Kellogg and Kellogg, 1933)
  Evolutionary: views it as an evolved, adaptive learning strategy, especially useful in childhood and high-stakes tasks.
• Cultural Drive: Culture itself accelerates evolutionary change by altering environments (general);
  Evolutionary: acknowledges this feedback loop as a driver of human uniqueness.
• Gene-Culture Coevolution: Mutual influence (e.g., lactose tolerance) (Laland & Brown, 2002).
• Cumulative Culture: Builds across generations, unique to humans.
• Evoked & Transmitted Culture: Environment triggers vs. imitation (Boyd & Richerson, 1985).
• Cultural Evolution: Rapid societal changes vs. slow biology.

Cultural Adaptations & Transmission: Human’s Superpower?

Culture benefits us by enabling us to change our behaviour extremely rapidly to fit environmental conditions.

Boyd and Richerson argue that this potential for rapid adaptation is one reason why the mind evolved an ability to generate and sustain culture.

For example, if temperature dropped dramatically many organisms, ill equipped by natural selection, might freeze to death unless cold-resistant mutations arise.
Humans, with their second mode of inheritance, can develop new technologies or approaches and pass them on to their offspring, enabling them too to survive. The ability to pass the new tech (‘technological inheritance’) is crucial and what differentiates humans from other species

Speed of Changes Dictates the Viability of Cultural Transmission:

Mathematical models suggest that cultural transmission is only adaptive when environmental change occurs at a moderate pace — not too fast and not too slow.

If the environment changed too quickly, inherited knowledge would become obsolete. If it changed too slowly, genetic evolution could keep up, making culture unnecessary.

🙋🏼‍♂️ Lucio’s note: the too fast/too slow may be misleading because culture is superior in almost all ‘speeds’
The speed of most changes probably fits within the range of superior cultural adaptations. And this is even truer with more advanced technology and increasing human capabilities.
Think for example, of the recent COVID pandemic: despite the extremely fast changes, humans were still able to craft a vaccine.
And despite the current temperature changes relatively slowly, it’s still too small a change and too fast for human evolution to adapt.

Boyd and Richerson argue that human culture likely evolved during the Pleistocene, when climate fluctuations created the ideal conditions: changes were significant but gradual enough that passing on knowledge (like shelter, tools, or hunting techniques) gave a survival advantage. However, this remains circumstantial rather than definitive evidence.

SHARPEST INSIGHTS

These are the insights that struck us the most.
We use the authors’ quotes and research, but the titles and interpretations are our own—and may not reflect the authors’ intent.
Credit for the insight goes to them; blame for the interpretation is on us.

Women have casual sex (almost) like men IF SAFE

🙋🏼‍♂️ Lucio’s note:
I’ve seen several arguments and counter-arguments for this batch of studies and this is the first time I’ve read something close to a final resolution

One of the most well-known studies on sex differences in casual sex was conducted by Clark and Hatfield (1989).

Attractive male and female students asked strangers of the opposite sex if they’d sleep with them. About 75% of men agreed—0% of women did.
The result strongly supported evolved sex differences: men are more open to casual sex, while women are more selective due to higher reproductive risks.

Later replications mostly confirmed the original pattern, even across decades of social change (Buss, 2016; Schmidt, 2017; Walter et al., in press).

But things change with Baranowski and Hecht.
Their research addressed women’s safety concerns by showing vetted photos with backstories and asking if participants would date or sleep with each person. In this safer setup, women’s willingness to date and have sex almost matched men’s. However, men still selected more partners overall—suggesting men are less selective, not just more interested.

David Buss, David Schmitt and Donald Symons all consider that this difference in behaviour with regard to casual sex reflects differing psychological adaptations in men and women.
But context—like safety and control—can shift women’s choices significantly.

Results from Baranowski and Hecht (2015) demonstrating that men chose to meet significantly more women compared to women choosing men, both to date and to agree to have sex with. Error bars represent ±1 SEM

Key Studies:

• Clark & Hatfield (1989)
  – Method: Students asked strangers to have sex.
  – Result: 75% of men said yes; 0% of women did.
• Replications (Buss, 2016; Schmidt, 2017; Walter et al., in press)
  – Method: Variations of the original setup over decades.
  – Result: Results mostly replicated—men more willing than women.
• Baranowski & Hecht (2015, Germany)
  – Method: Participants rated vetted opposite-sex photos for dating or sex.
  – Result: Women’s consent matched men’s when safety was assured, but men still chose more partners.

🙋🏼‍♂️ Lucio’s note: I missed how the chart and the authors’ claim can match
It’s not fully clear to me why the authors say that ‘Interestingly, however, men wanted to meet significantly more potential partners than women‘. If by ‘meeting’ the authors refer to the chart’s ‘date’ condition, then it’s not a significant difference in my opinion.

Human cooperation depends on the environment

Speculatively, hard times might favour individuals who are likely to cooperate – there is a powerful need to work together to eke out a living from a hostile environment – whereas good times might favour individuals who are somewhat more selfish – since there is plenty for all, individuals can more easily lead a productive life on their own.

If we imagine that the environment favours cooperators, then this phenotype will profit at the expense of more selfish individuals.

If such conditions were to obtain for a long period of time then selfish individuals would probably die out, but if the environment fluctuates back and forth comparatively rapidly (over a cycle of, say, 100 years or so) then under different conditions the selfish individuals might find themselves at a fitness advantage and their numbers would increase at the expense of cooperators

We’re getting less intelligent

This is something that worries me for the future of humanity:

That the brain developed despite these costs is clear evidence that the brain didn’t get bigger by accident, there must have been advantages in order to outweigh these costs. In fact, there is some research which suggests that our brains have been shrinking for the past 10,000 years or so (Liu et al., 2014). This may be because nowadays we have less need to be individually smart, relying increasingly on the products of culture and teamwork. Whatever the reason, if this research turns out to be correct it shows that evolution gives us the size of brain we need and no bigger.

Coolidge effect is cross-cultural

One key psychological gender difference is men’s stronger response to novel sexual partners, also called ‘Coolidge effect’.

The Coolidge effect—a rapid return of sexual interest when a new female is introduced—is now known to be a cross-cultural feature of human males (Symons, 1979; James, 1981; Hamer and Copeland, 1998).

Interestingly, a small number of studies suggest that, at least for rodents, females may also demonstrate a Coolidge effect, albeit to a lesser extent (Lester and Gorzalka, 1988).
As for human females the question currently remains open as any such studies remain to be published.

This supports the idea of an evolved tendency toward non-full-monogamy, since this adaptation may be hard to explain without an evolutionary history of ‘straying’.

🙋🏼‍♂️ Lucio’s note: the coolidge effect may be stronger among men with unrestricted sociosexuality
As part of an adaptation package to orient more towards short-term and uncommitted relationships, and sexual escapades.
Also see our article on ‘cad psychology‘:

Industrial societies must suppress kin-reciprocity (nepotism)

Canadian evolutionary anthropologist Jerome Barkow has suggested pre-industrial societies are a lot closer to our evolved psychology than industrial societies (which he calls ‘complex societies’). He suggests that, in order for industrial societies to work, kin-selected altruism has to be suppressed and labelled ‘corruption’ or at least as ‘nepotism’ (Barkow, 1989)
Moreover, it is when these complex societies break down, as in revolution, that such strong nepotistic tendencies reemerge (Barkow, 1982).

I believe that more than for ‘industrial societies’, this is true for democracies and well-functioning societies.

QUOTES

On the inherent ‘eugenics’ of reproduction and sexual market dynamics:

In a sense, all sexual beings participate in a form of eugenics, albeit unconsciously. There is evidence to suggest (see Chapters 3 and 4) that when an animal (including a human animal) selects a sexual partner it does so, among other things, on the basis of characteristics that are indicative of good genes

On survival VS reproduction:

If natural selection is survival of the fittest then we can think of sexual selection as ‘survival of the sexiest’

On big VS small and the misunderstanding of ‘big being more dangerous’:

It’s not the big organisms that are most likely to kill you, it’s the ones you can’t even see

On cooperation VS competition and competition trumping cooperation:

But whereas cooperation is well documented in many species, competition is rife in all. Animals, in a sense, compete to become ancestors

On the importance of social status hierarchies:

The hierarchical structure of human societies which, surely, is one of the most important reasons why, for good or for bad, humans dominate the globe.

On fear as an evolutionary emotion:

If there is one core emotion that has clear survival implications it must be fear. People who have no fear do not make for good ancestors

On the power of evolutionary psychology to convince sensible and smart men with the power of its logic and data:

As an anthropologist from the cultural relativist school, Brown did not believe in cultural universals and bet Symons that he could find a culture in which each of Symons’ proposed universal sex differences was reversed.
He didn’t win the bet. In fact, he completely revised his opinions. After studying a large number of cultures Brown discovered that there were more than 200 characteristics common to all cultures

Lucio’s Analysis

The book is great, and here are some suggestions for the authors to consider for the next editions:

Include SDO to homology/coalitionary aggression

A reference to social dominance theory and its measure (social dominance orientation) will help readers bridge the gap from evolutionary psychology, to social psychology and power dynamics.

Add a note to ‘rate of change for cultural transmission to work’

The current framing of ‘perfect sweet spot’ between too fast/slow for environmental change may risk overstating the limits of cultural transmission.

In reality, culture often remains superior to genetic adaptation across a wide range of change speeds.

Most real-world environmental shifts likely fall within a bandwidth where cultural solutions remain adaptive—and often vastly more efficient—than waiting for genetic evolution. This is especially true today, with the exponential growth of technology and communication.

Consider the COVID-19 pandemic: despite being a fast-mutating virus, humans developed and distributed effective vaccines within a year.
On the other hand, climate change is relatively slow on a generational scale, yet still too fast and too subtle for genetic adaptation to offer any viable solution.

It is culture—through science, policy, and organized action—that remains our best practical response.

I’d love for the authors to amend the text accordingly (or criticize this point if they find it invalid).

Speaking of which:

Expand cultural evolution

I’m biased because after reading Henrich’s work, I think that evolutionary psychology is still underestimating the impact of culture on evolution, civilization, and growth trajectory.

That said, I’d love the authors to include Henrich’s work and talk more on cultural evolution and its potentially growing impact on human societies:

• The Secret of Our Success
• The WEIRDest People in the World

They can find some extra space by cutting the following:

Streamline and simplify

Including:

Cut Some Tangents

The book is too good to leave any low ROI paragraphs hanging around.

I felt the book could be even better, replacing some tangents with more evolutionary psychology, or completely removing them.
For example:

• Person-first language movement stemming from ‘autistic people’. It’s an important advancement of civilization and humanity to amend our everyday language, but it’s tangential
• Birth order research could be streamlined
• Margaret Mead: She features twice, both times including the criticism of her work and once even the evolution of her thought. Yes, maybe she’s been overly vilified, but in my opinion her impact has still been largely negative.
  I may be right or wrong, but the point is that discussing individual authors should not be part of the text, in my opinion
• Trim out the ‘defending evolutionary psychology’ angles: Sometimes I feel it can come across as defensive, for example that ‘early environmental calibration (…) provides further artillery against the view that evolutionary thinking is necessarily deterministic. The authors are perfectly right, but I don’t think we need any artillery. We can let science do the talking.
  • Consider removing ethical notes:

For example:

in a subject that treats relationships in such a cold and calculated light, it seems reassuring to discover that both men and women value love as of primary importance (…) When we consider less permanent affairs things begin to look less romantically rosy.

And a bit later:

Before we begin to feel let down by the lack of fidelity that this suggests for our female ancestors we should also bear in mind that it takes two to recombine their genes: both sexes are equally tainted by such findings!

I smiled at this, and we all understood what the authors meant.
Not sure though, whether it belongs here, also because this may be misconstrued as judgmental towards women.

Add brief descriptions to the list of ‘key concepts’ opening each chapter

Given the target audience and the strengths of this book, I’d consider making some parts of the book even more approachable.

Some ideas:

• A list of ‘key concepts and definitions’ before each chapter. The authors already provide a list, a fantastic approach to ‘prime’ the brain for the upcoming learning. A quick summary for each will make it even more useful. You can move the glossary definitions to that opening paragraph
• Combine all related concepts into one single chapter. For example, psychopathy and balancing theory are spread across at least two chapters. Combine them all in the chapter where you discuss psychopathy the most.
• Group similar and sub-theories together. For example, I believe the handicap principle is part of the larger ‘good genes’ principle. Combine them together
  • Introduce all relevant terms or variations first, then use the most widely recognized one. For example, note that Zahavi’s handicap principle is now “honest signaling,” and use “honest signaling” thereafter.
• Add a ‘common misunderstanding section’, which may be very helpful for freshmen who dabbled into pop-psychology before starting uni.
  eg.:
  • ‘Great chain of being’ and ‘continuous improvement’ instead of a messy random walk that the environment weeds out, etc.;
  • ‘Storytelling fallacy’, or the tendency of many people to come up with a just-so story and passing it for evolutionary psychology, a popular approach that undermines the validity of evolutionary psychology, etc.)

Deepen the basics, including pictures and diagrams

It was perfectly done with the example of ‘blueprint VS recipe’.
Do the same for topics like:

• Genes vs. DNA vs. Alleles vs… : these concepts and how they work are all fuzzy for beginners, clarify it them
• Genetic VS biologic, a subtle difference that took me years to grasp
• Evolutionary stable strategy

To avoid overloading the text, cut down on the history of Charles Darwin and Mendeleev.

Rank Theories From Largest Contributors to Smallest

To improve clarity on complex topics, present the main, most well-supported drivers first—those with the strongest empirical backing and largest effect sizes—and then list additional or more speculative contributors.

You could also add a final table with a ranking.
Yes it’s simplistic, but it may help students organize information.

For example, discussing altruism, this is how a tabled rank may look like:

“Evolutionary Drivers of Altruism, Morality, and Cooperation: A Ranked Framework”
(by Lucio Buffalmano)

⚠️ Revisit the claim of nonpaternity rates

The authors write:

Also in England, via genetic testing, Baker and Bellis (1995; 2014) have found that about one in five children could not be the offspring of their supposed fathers.

The authors quote Robin Baker, the author of Sperm Wars, a book that, back then, I found to raise some important red flags.

One in five seemed hard to believe based on what I knew.
So I asked ChatGPT for confirmation, which replied:

That claim is misleading. Modern genetic studies in England and other Western countries do not support a 1-in-5 (20%) non-paternity rate

AI mentioned studies supporting rates of around 1-4% and reaching up to around 30% only when paternity is already disputed (e.g., men requesting tests due to suspicion).
That is in line with what I had previously seen and read.

I think the authors referred to cases with pre-existing doubts, but they could make it clearer to avoid possible misunderstandings.

REVIEW

Evolutionary Psychology: An Introduction is one of the best available books on evolutionary psychology we’ve read and reviewed.

It may be the best introductory book to the field of evolution and evolutionary psychology.

It distills complex evolutionary principles into a clear, engaging guide to how evolution shapes the human mind and social behavior.

Check the best evolutionary psychology books or get this book on Amazon: