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In this video at 42:06, Daniel Dennett posits that our big brains are:

The human artifice or version of the peacock's tail.

Peacocks have sexual dimorphism - it's males who exhibit the costly signal of showing off a big, colourful tail.

Now, humans are more special, because there are certainly no differences in the cognitive potential of men and women. Yet, there seems to be evidence for each gender being driven by different interests.

Thus my question: has human intelligence evolved as a costly male signal which has, over time, been passed to females?

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    $\begingroup$ You cite an opinion piece as "plenty of evidence"? $\endgroup$ Commented Nov 4, 2019 at 16:52
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    $\begingroup$ Actually, I read most of the article. Though it cites research, it is an opinion piece. Opinion pieces cherry pick and misrepresent in order to support their bias. To truly evaluate the worth of this opinion piece, one would need to read all the cited studies (to see if there was misrepresentation, to see if it was a good study, etc.) As to your (horribly biased) statement that the fact that women have contributed less to science than men, you need to look no further than how women in science have been discouraged and discriminated against by men. $\endgroup$ Commented Nov 4, 2019 at 17:05
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    $\begingroup$ For example, read The Double Helix to see first hand how Watson stole - that is, used without her permission or knowledge - the work of Rosalind Franklin to deduce - to deduce the fact that DNA was a double helix. They could not have done it without her Xray crystallography work. As a Molecular Biologist and physician, perhaps I know a bit more about "gender politics" in Science than you. $\endgroup$ Commented Nov 4, 2019 at 17:08
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    $\begingroup$ "I don't engage in gender politics..." You already did by claiming that the differences in scientific contribution between men and women is vast, or as you've said, "little compared to men." $\endgroup$ Commented Nov 4, 2019 at 17:27
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    $\begingroup$ There might be an interesting question buried in here somewhere (along the lines of "is intelligence a sexually selected trait in humans?") but it's buried in unnecessary non sequitur and unsupported claims about male and female humans. $\endgroup$
    – Bryan Krause
    Commented Nov 4, 2019 at 20:22

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No

Think of it this way, what would you actually expect to see if this hypothesis was true?

  • Do humans actually show significant differences in relative brain size between sexes, like horn development in ungulates or tail feather length in peacocks, either currently or in the fossil record (answer: no).
  • Is intelligence a significantly sexually selected trait in other apes (answer: no).
  • Is intelligence a primary factor in mate selection (answer: not really. There is a positive correlation between intelligence and mate selection, but there are many other factors such as perceived social status, dominant behavior, personality, etc. that explain more of the variance. It's likely intelligence is more correlated with general health than a signal for sexual selection. This is why rock stars and athletes have large numbers of mating opportunities and scientists do not).
  • Are there significant selective differences between intelligence in males and females (answer: no. Intelligence is also positively correlated with mate desirability in male mate choice).

What these authors are arguing is that human brain size originally evolved as a sexually selected adaptation, and then selection proceeded so fast that it obliterated all evidence of it originally being sexually selected. Some authors I've seen argue this base argument on incredulity on the fact that human brain size evolved so fast. That's not a solid hypothesis based on evidence, that's just handwaving and argument from incredulity. It's making an argument based on special pleading to ignore the hypothesis with the simplest number of steps in favor of one that requires a more unlikely sequence of events to occur, and one that is not based on any actual evidence.

The idea that key features of "humannness" originally evolved in one sex and became established due to drag-along selection has been thrown around for decades with very little actual evidence. Richard Dawkins in The Ancestor's Tale suggested that bipedalism in humans originally evolved in males as a display behavior to look more attractive to females, and Owen Lovejoy has been promoting the hypothesis that bipedalism in humans evolved to allow humans to carry helpless infants. All of these cases are based on handwaving and little actual evidence.

Adding to this is the fact that in nature we generally don’t see “drag-along” selection, where selection favors a feature in one sex and it gets fixed in the other sex due to selection in the first sex. We especially don’t see it in traits that result in a huge penalty in reproductive fitness and hence have high selection pressure or represent a high-risk, high-reward adaptation. Nipples in male mammals may be one example, but nipples don't consume 20% of human's metabolic budget and put huge pressures on the female reproductive system.

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  • $\begingroup$ Thanks for putting the time to write this thorough answer. $\endgroup$
    – anon
    Commented Jan 19, 2021 at 22:20
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"has human intelligence evolved as a costly male signal which has, over time, been passed to females too, but whom are just not as interested to use it to attract mates?"

(I am ignoring that last part)

So you suggest intelligence (the modern human brain) evolved solely as a sexual dimorohism which then migigated over time?

I find that particular combination unlikely because intelligence would somehow need a sex-chromosome dependence which later was somehow lost. I don't think sexual dimorohism in intelligence can by seen in any mammals, and losing it again is unlikely as well.

But I can't disprove your idea completely: It seems the brain specific expression pattern is quite different in males and females. Also some brain specific genes were found as additional copies on sex chromosomes.

https://www.nature.com/articles/ncomms3771

With either of these 2 facts alone there is at least some miniscule potential that your hypothesis could be true!

(So you can argue gene duplication to autosomal chromosomes or expression levels being influenced by sex chromosomes.)

Ps: But it's equally (un-)probable that intelligence at first evolved in women only.

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    $\begingroup$ I don't know if this matters, but it bothers me: the N's all had neuropathology (autism, I'll assume Parkinson's, etc.) There are neuropatologies more common in men than women and vs. versa. Does this affect the validity of the study? I don't know, but I'd rather see this comparison done on normal tissue. However, I don't doubt there are differences; testosterone has a significant effect on behavior which would imply the mind/brain. The study linked in comments shows a difference in white/gray matter use during certain tasks in men and women, but not a difference in matter per se. $\endgroup$ Commented Nov 5, 2019 at 17:34

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