why would a human female have a sexual display despite male-biased operational sex ratio?

In human society there is a male-biased sex ratio, due to female child rearing, which results from anisogamy. Human females sometimes expend great amounts of energy and resources performing display acts and doing things to attempt to improve their apparent quality to males. Human males tend to be eager, despite a certain level of socially imposed monogamy, and many males will mate with a low quality female. Why do human women do sexual display behaviors, when there are so many eager males to choose from?

  • $\begingroup$ Your question is not clear. Can you please add some more details to clarify it? $\endgroup$
    May 9 '17 at 5:10
  • $\begingroup$ @WYSIWYG did my edits clarify enough/at all? $\endgroup$
    – 5r9n
    May 9 '17 at 5:17
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    $\begingroup$ @WYSIWYG What is unclear about this question? Seems perfectly clear to me. Although I think more recent research would question the basic premise of human operational sex ratios being purely male biased, but I think we've agreed in meta not to oppose questions based on incorrect premises (and likely a good answer would address that possibility). $\endgroup$
    – Bryan Krause
    May 9 '17 at 5:38
  • $\begingroup$ Okay.. I understood the question but I guess what you are talking about is a recent phenomenon and is not likely to be shaped primarily by evolution. $\endgroup$
    May 9 '17 at 6:03
  • $\begingroup$ Because it is not just about mating and sex. Evolutionary it is also about care and bringing the offspring through life together. $\endgroup$
    – skymningen
    May 9 '17 at 6:17

Sexual arms race.

There is a fine and internally consistent theory that this strategy by females evolved to oppose the strategy of infanticide by males. Males of many species including primates and possibly humans can increase their own genetic fitness by killing infants that are not their own. This frees up attention and physical resources of the female to instead have the baby of the infanticidal male. Lions are famous for this. But this is in opposition to the genetic fitness interest of the female, who just invested a bunch of efforts gestating and rearing an infant who was then killed.

My favorite writer on this is Sarah Hrdy. From the Wikipedia article on this\

This is where the idea of sexual counter-strategies comes into play. Hrdy theorized that by mating with as many males as possible, particularly males who are not part of the colony, mothers are able to successfully protect their young, as males were unlikely to kill an infant if there was the slightest chance that it might be their own.

This explains why women have the sexual displays referred to in the OP. Other aspects of female human biology match. Humans keep big breasts so they always look like they are lactating (compared to other animals) - to keep males guessing. There is no external sign to indicate when a human is ovulating. Females of other species are receptive and mate when they are ovulating - humans can mate any time.

A strategy of keep the guys guessing. If one time he had sex with a given female, probably he shouldn't kill the kid. Maybe it is his?

An interesting (& extremely arguable!) corollary to this is the premise that human culture in its entirety is the male countermeasure to this prehistoric female defense against infanticide: that male dominated culture is a method to ensure paternity.


Based on what is currently known, I would say that while females might find sperm readily available, it is common for human males to not only provide sperm but also help rear the offspring (e.g., provide care, financial support, food, transportation). So, they might provide sperm to a woman they're not impressed by (by "impressed," I mean convinced the woman has whatever characteristic the sexual display is supposed to exhibit), but they only offer rearing investment to offspring of a woman they are impressed by. So, basically, the woman is making a demonstration in order to garner investment from the male. I think there's more to it than that, but this answer is based on what is currently known and robustly supported in the literature.

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    $\begingroup$ do you have a link to that literature? $\endgroup$
    – a tiger
    May 9 '17 at 9:10
  • $\begingroup$ By literature, I am just referring to current theory, not any specific articles. I have other explanations that would be regarded as more speculative. $\endgroup$
    – sterid
    May 9 '17 at 10:18
  • $\begingroup$ "Literature" is not the same as "theory". "Literature" means scientific papers. Guesses are "hypotheses". $\endgroup$ May 9 '17 at 13:55
  • $\begingroup$ I mean, prevailing theory. What part of this are you challenging? $\endgroup$
    – sterid
    May 9 '17 at 15:29

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