Sperm Wars: Summary, Review & Criticism

sperm wars

Sperm Wars (1996) looks at dating and sex from an evolutionary biology perspective and through the slightly controversial perspective of “sexual conflict“.

Bullet Summary

  • Women can gain by pitching one men’s sperm against the other with back-to-back sex with different partners
  • The strategy of focusing on fewer children can be more useful than going for quantity
  • When you’re poor daughters are better and sons are better when you’re very resource-rich (thus, the Chinese did it wrong for decades)

Full Summary

About the Author: Robin Baker studied zoology and earned his Ph.D. with a thesis on the evolution of the migratory habit in butterflies.
He later left the academic world to focus on his writing.

Note: Skipping the Stories

Sperm Wars introduces lots of stories that go along with the theory.
Some of the stories are interesting, some even funny and, some have been noted, can also function as entertaining soft-porn reading.
I will skip the stories for this summary.

The Arms’ Races Between Sexes

Sperm Wars paints a somewhat bleak picture for those like me who see genders as complementing each other.
Instead, it shows Robin Baker shows how males and females in a relationship can have major incentives in tricking and deceiving one another:

  • Women hide their fertile days because:
    • She can more easily deceive her partner if she wants to cheat
    • Keeps her partner interested in her at all times
    • Confuses herself as much as her partner, leading to more routine sex
  • Women are more likely to have extra-marital affairs during ovulation
  • Men ejaculate more when they have been away from their partner (unconsciously preparing for possible cheating and sperm wars)
  • When women change partner she almost always moves up

The No-Fapping Big Lie

There is a big craze around the Internet on “no-fapping”. Interestingly, Robin Baker says that it’s a lie that men and religion impose on men to defend themselves from single men.

The author makes a big case that masturbation helps in sperm wars because it “cleans” the pipe of older and less lively sperm. Instead, a man who masturbates has more lively sperm which is more suited to engage and win sperm wars.

Note: Probably true
Eric Castle from the Mayo Clinic says that masturbation doesn’t have such a big effect on conception.

Cheating Tendencies

Sperm Warms says that women are much more likely to have sex with a man who is not their partner during their fertile days and is much less likely to use contraception (data for this statement is missing).

Soon after the cheating, however, there is a tendency for her to run back to her long-term partner.
Reason why?
So that she can be inseminated by both and thus promote sperm competition.
Let the best ejaculator win.

What’s Important to Have Big?

The author says that penis size matters little in sperm competition.

Instead, the testes’ size matters a lot as more sperm gives a major advantage in sperm competition and increases the chances of fertilizing the egg. Especially in non-monogamous species, which is why males of non-monogamous species have larger testes.

The author says women are interested in their buttocks more than the penis and muscle (Body Language of Love confirms this).

Also, read:

Quality As Important As Quantity

The author says that in poor conditions where many children die, people tend to produce lots of offspring.

However, Baker says that a strategy of focusing on fewer children and nurturing them properly, and giving them more resources is equally effective.
One single child can also work, but it’s very risky as it can fail spectacularly if the child fails to reproduce.

A balance between investing in resources before having children and actually having children is important.

Poor People Get Cheated More

The author suggests that poor men get cheated more.
Men of higher wealth and status instead obtain partners earlier, reproduce earlier, and are more likely to do the cheating.

Read more on cheating, faithfulness, and infidelity:

People Pick Gender of Children Depending on ROI

Poor people are more likely to have a daughter because daughters are more likely to guarantee reproduction -and you can be sure that the child is hers- and are more likely to marry up.

It’s best to have boys for high-status couples instead because men with lots of resources can have multiple children that they can all cater to.

And indeed, Baker says, that’s what we see: American presidents, for example, have 60% of sons.
It’s not yet clear how women can “decide” which gender, but it seems to be the woman who achieves the gender bias.

My Note: Small sample size
the theory might be good, but the example is not. I believe that the number of presidents’ offspring is too small to derive any meaningful data.
Different researchers have reached different conclusions here, so this might be true, but I’m not 100% sure as of now. If it’s true, it’s by a small-ish factor.
Also read: Fooled by Randomness and How to Lie With Statistics.

Rape & Prostitution

The author says that rape and prostitution can both be effective strategies.
Indeed prostitution might have been so successful on our part that, in a way, we are all sons of bitches (that one had made me chuckle :).

There are also many drawbacks though, including the risks of disease.

The author wonders how come rape is not more common since it can actually be successful.
One of the reasons is that it’s risky. It often involves a physical fight and also a high risk of retribution from possible partners, family, or tribe members.
He postulates that most men can become rapists given the conditions because most wars, which provide a safer environment for rapists, show widespread raping.

Once a woman has been raped, it might be good for her to conceive though, and the author says that a woman is more likely to conceive from rape than from routine sex with her partner.
The author also makes the interesting claim that women often stick with abusive men who successfully raped them because they “proved their strength” (VS a man who tried but didn’t succeed).

Prostitution has been so successful that, in a way, we are all sons of bitches

What Men & Women Like

Men mostly look at the beauty, age-related to fertility- and reproductive fitness.
Women look a lot at status.

My Note: Depends
As Aronson explains in The Social Animal women also behave like men and look at beauty mostly when the status is the same or difficult to assess. Otherwise, they go for status.

Crucially, and this is what I credit to Sperm Wars the most, is the notion that men respond to traits such as weakness and dependence which can indicate fidelity.
Also, read:

Strategies for Reproductive Success

The author says that men are much more similar to themselves than women are to other women.
However, they also pursue four different strategies for reproduction:

  1. Bisexuality
  2. Sperm warfare specialization
  3. Avoiding sperm warfare
  4. In between avoiding and engaging in sperm warfare (the majority of men)

The strategies tend to be in equilibrium in society.
Basically, it’s not true that everyone should try to be as “alpha” as possible. Because there are enough sperm warfare specialists a strategy of monogamy can be equally or more (or less) effective.
It seems best instead to pursue your strategy also based on your biological predisposition.

Long-Term Relationships Can Be Most Successful

Although few people pursue a lifetime of pure monogamy, most find success in long-term relationships.
Amongst the advantages, there is that of not getting caught cheating and much, much lower risk of diseases.

Sperm Wars Criticism

I have done quite some research on this book, but instead of writing a coherent piece and rebuttal, for which I don’t have enough knowledge, I will write here some of the most important points:

  • Robert Martin, a biology Ph.D., writes in Psychology Today that there is “humans have no special biological adaptations to cope with sperm competition”.
  • Killer sperm is, at best, unproven: Studies show inconclusive results on “killer sperm” in both humans and animals
  • A study suggests that sperm traits are female-inherited, which means that male competition won’t affect sperm as directly as Sperm Wars implies
  • Non-paternity rates are much smaller: The author reports that 10% of children are not fathered by a long-term partner. That’s a lot -albeit it would still leave 90% of faithful cases-, but it’s also not true. If you take DNA tests as a father because you are not sure, then your chances of not being the father are around 1 in 3. But on the overall population the median among estimates is 3.7% (and even lower for those fathers who don’t have any suspicions) One of the sources is here and another one here)

Conclusions of Criticism

The idea I have grown and that I am happy with -and which reduces my cognitive dissonance (Festinger, 1957)- is this: there is no doubt, of course, that we have all evolved several tools to further our agendas in the reproductive arena.

And that sometimes these tools pitch women and men against each other.
Jealousy and bigger testes in humans than, say, gorillas are probably examples of males’ tools against females’ possible cheating.

However, the war of the sexes is nowhere near as bad as the author makes it out to be and cooperation is more successful than covert cheating -albeit cheating while the other partner suspects nothing can also lead to high rewards in such a system-.

Sperm wars, also, played a role in human evolution and still partially do. But not nearly as badly as the author says. There is also no proof -and so far it seems more likely no than yes- that “killer sperm” and “blocking sperm” even exist.

sperm wars

Real-Life Applications

Learn Nature, Then Choose What to Follow
I think a great takeaway here is that nature can be fucked up and that a lot of our evolution can be maladaptive as well.

Thus, learn biology, and then reflect on what you really want and what’s really good for you and the people around you.
Because that’s not necessarily what our prime urges might push us into.


  • Unproven Claims Presented as Fact

I really wonder why the author presents claims that are unproven and highly speculative without warning the readers about their very nature. He could have easily told they were speculation and he would have avoided so much criticism.

Was it a case of looking for sensationalism?
To remain in the biological realm I would call such choice maladaptive.

  • Homosexuality / Bisexuality Explanation

The author tends to explain almost every behavior in light of “better suited for procreation”, which in my opinion is a very common mistake that does not take into account that, when so thousands and thousands of traits are interplayed, a lot of behaviors and mutation are just purely out of chance.

However, out of all the theories in Sperm Wars, the one on homosexuality as a maladaptive offshoot of adaptive bisexuality made the least sense to me. I won’t go into details but it seemed a rather poor theory to me.

  • No References

Attention: the author makes it clear that Sperm Wars won’t leverage references because it’s the popularization of his other work, Human Sperm Competition, which is heavily referenced.
However, as a guy interested in both the practical application of science and the science itself, I would have liked an in-between version.

  • Confuses Correlation With Causation 

The author says that since rape is common during wars, then men must all have a tendency to rape.

However, there is also a correlation element, such as men who go to war are more likely to be violent themselves maybe?
And of course, a situational element, where an environment full of violence can lower the bar for more violence.


  • Eye-Opening Read on Sex Arms’ Races

If you have not read many books on evolutionary biology Sperm Wars can be a shocking eye-opener.
In a good way.

  • Good Resource for Understanding People

There are many good concepts here, and you will learn a lot about psychology and human behavior.


Sperm Wars has some eye-opening content but also, unluckily, quite a few unfounded claims that cast some shadows on the whole.

It’s difficult to rate this book for me.
Part of me loved it and it had a lot of new information that led me to a deeper understanding of the arms race to reproduction.
But it also has a lot of conjectures, key disproved information, and no scientific reference.

When I first read it I almost wished the theory was true because it presents such a beautiful and elegant theory that explains things so well.
But beauty and elegance are not synonymous with truth.

Overall, I would give Sperm Wars four stars for the value it provided me the first time I read it, and zero stars for scientific to warn readers that they must do their own research with this book.
And a big strike against it for scientific integrity: some information in “Sperm Wars” are highly misleading. And the author does nothing to warn the readers his conclusions are highly speculative at best and either unproven or with plenty of discordant evidence available.

Check the:

or get the book on Amazon

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