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Memetics And Sexual Selection

November 9, 2013

I am fascinated with memetics, so I was drawn in by a post on this blog, as it both discusses memetics and is an example of memes in action. My comments on some of the common memes relating to the study of human sexual selection it invokes are below:

“Females, on the other hand, generally can’t produce more than 1 fetus a year and therefore have only a few chances per lifetime to pass on their DNA and many eager suitors. Therefore they evolved to be a bit more selective.”

This notion of men being evolutionarily motivated to be sexually promiscuous and women being evolutionarily motivated to be sexually selective has been around long enough to be firmly established as conventional wisdom. However, it ignores sperm competition and also projects modern values and family structures into the past. Regarding sperm competition: it is every bit as evolutionary advantageous, if not more so, for a female to have multiple sexual partners as it is for a male. The fact that a woman can only produce one fetus per year does not mean that she needs to be “more selective” about who she mates with, because she will never expend more than a handful of eggs to produce one fetus, meaning her energy budget per conception is low relative to that of a male. What female genes prefer is to have their carrier mate with as many men as possible in a short amount of time, specifically right around ovulation, and let their sperm compete internally. This guarantees that the woman will be impregnated by the highest quality sperm. As far as a woman’s genes are concerned, the more the merrier: more sexual partners only raises the stakes, to her advantage, and costs her virtually nothing in terms of biological resources. In fact, while the biological cost for a woman to have sex with one more man is negligible, the biological cost for a man to have sex with one more woman is significant; if he expels his sperm into a less-fit female, he will have fewer with which to fertilize a more promising candidate. While males’ sperm supplies are necessarily plentiful, they are not limitless, and it takes trillions of them to fertilize just one egg. Sperm spent in one place means less (or none) spent in another. These facts turn the conventional reasoning about men’s promiscuity and women’s selectivity on its head, and may partly explain men’s penchant for physical attractiveness (if a man is going to attempt to impregnate a woman, his genes want him to be very discriminating about screening for fertility beforehand) and women’s relative indifference (it costs a woman relatively little to let a man enter the competition, and she doesn’t have to be as discriminating on the front end because she can let the sperm sort itself out — the fittest sperm will, by definition, be most likely to win). To use a set of analogies, for a man, attempting to impregnate a woman is like investing scarce capital in a risky start-up venture, whereas for a woman, becoming pregnant is like being a spectator at American Gladiator.

“How did they select? A number of factors were important. First, they wanted a male with ‘good’ DNA, whatever that means…. Second, they wanted a mate who would invest his time and resources in the children while they were immature and vulnerable, thus increasing their chance of survival.

Given the priorities of females, males evolved in one of two directions: either become stronger and more handsome, or become a convincing potential husband and father.”

This meme relates to the second fallacy, the projection of modern values and family structures into the past: the nuclear family (at least among humans) is an invention of the previous century. Humans are social primates; in evolutionary history, they have spent most of their time living in tribal extended family groups. Individuals remained part of the same group throughout their entire lives, and every member of the group depended upon every other member of the group for their survival, and likewise invested their time and resources in the maintenance of the collective livelihood. Our evolutionary ancestors did not segment themselves off from the tribe so they could live in pair-bonded matrimony, to thrive or perish by their own fortunes. Individual survival was simply inconceivable. The very concept, and requisite context, of a deadbeat dad had to wait several millenia to be invented.

Supposing, however, that male sexual strategies did diverge in the directions suggested (let’s call them “bad boys” and “good guys”) a female’s best evolutionary strategy would be to attempt to become impregnated by one of the “bad boys” while convincing one of the “good guys” that the offspring was his. This gives her the best of both worlds, allowing her to receive the support of a dedicated provider, while ensuring that her male offspring and further descendants will inherit the more fecund genetics and behavioral tendencies of the “bad boy”. This reproductive strategy is in fact indicated theoretically in humans by the masking of the ovulation cycle, and experimentally in humans and other species by the incidence of extra-pair copulation (“your daddy ain’t your daddy and your daddy don’t know”), as revealed by random paternity testing.

“If humans would not have learnt to tame this ‘selfish gene’, they would still be leaving in caves killing each other for mating opportunities.”

It’s not at all clear that humans ever lived this way. The mating strategies of social primates (as well as other species) tend to fall on a continuum between the extremes of free love on one end and harem-keeping on the other. In free-loving species (bonobos being the most prominent example), sex fulfills the role of providing social cohesiveness, much like grooming. There is little to no male rivalry, and conflicts are settled through mating. There is relatively little physical differentiation between sexes (sexual dimorphism) on the basis of size and strength, the males have large penises and testicles, relative to the size of their bodies, and female ovulation is masked. This indicates that reproductive competition between males takes place largely on the level of sperm. In harem-keeping species (prominently exemplified by gorillas), social groups tend to consist of one dominant male and many females, with most non-dominant males being marginalized or expelled completely, living solitary lives in the wilderness. Disputes are settled by physical force, and males are substantially bigger and stronger than females, while their genital size is small, relative to their body size, and female ovulation is advertised. This indicates that competition between males takes place largely on the physical level, with dominant males preventing subordinate males from having sexual access to females.

On the sexual dimorphism/genital-to-body-size ratio scale, humans fall somewhere in between gorillas and bonobos, which indeed indicates a blending of mating strategies, though plenty of evidence places us genetically closer to the bonobo end of the spectrum.

“The millions of years of genetic evolution that produced these instincts did not count on us figuring out that you could have sex and not get pregnant. That might potentially turn the evolution in a different direction with only people, who are committed to their partners and children, being able to pass the gene, as in other cases females won’t be getting pregnant. Raising children requires a lot of time, effort and care that only compassionate, caring, kind and loving parents can provide. People, who do not possess these qualities, are highly likely to be more interested in using contraception to prevent pregnancies. As the result, empathy, compassion, care, kindness and love might win in a longer run in human evolution.”

For all of human history, most sex has not led to pregnancy. Even in the absence of birth control, the incidence of copulation relative to the incidence of pregnancy is quite high. As with bonobos and other species that mate throughout the ovulation cycle, rather than only during estrus, human sexuality is not “just for reproduction” but also serves, perhaps even more primarily, as a social adhesive. Most modern couples use sex as a way of experiencing closeness and intimacy on a physical and emotional level much more frequently than they use it for making babies.

And it seems to me that more thoughtful, compassionate, and loving individuals are more likely to use birth control, at least for most of their lives, not less, and that the evolutionary spoils of fecundity are more likely to go to those who are more thoughtless, brash, shortsighted, and self-serving, at least when they are young. Population grows faster when individuals reproduce earlier in life rather than later, owing to a shorter generation time.

For detailed scholarly treatment of these topics, I recommend Sex at Dawn and Sperm Wars.

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