[thursday0987]

morality aside, the men who donate sperm will have an outsize influence on the genetic diversity of our species.

Think ghengis khan except on a smaller scale.

also interesting to think about the implications on human evolution over long periods of time:

will humans still have a 50:50 gender ratio of men to women? seems like sperm donation facilitates a much lower number of men required to maintain populations.

will humans still desire relationships with the other gender, or will we be more like bears (men show up for 20 minutes, do the deed, then don't help raise the kids)?

lots of interesting implications to consider.

[mpalczewski]

In general 50:50 ratio is observed in most species even with great variability in male reproductive success because the expectation for offspring is equal between male and female so the selection pressure generally keeps it close to 50.

[yorwba]

> the expectation for offspring is equal between male and female so the selection pressure generally keeps it close to 50

It's the other way around: the selection pressure drives the expected offspring to become equal. The expected offspring for an individual of a certain gender is (total offspring)/(number of individuals of that gender). The fewer individuals of one gender there are, the higher the expected offspring and the greater the selective pressure to produce more offspring of that gender. So the gender ratio is self-stabilizing.

[FabHK]

This is really a quite surprising and profound fact, worth pondering.

Naively, one would think that if you have (in some antediluvian setting) village A with 50 men and 50 women, and village B with 10 men and 90 women (and children born with that gender ratio, respectively), that village B could "produce" way more offspring and grow faster.

A naive "group selection" view of evolution might even predict something like that to happen.

But, in village B, there is an incentive, so to speak, to cheat and have boys at a higher ratio, because that would increase expected total number of offspring. So, the gender ratio stabilises around 50/50 - a Nash equilibrium, if you will.

[hrolfgar]

Sort of like the prisoners' dilemma; at the end of the day, the selfish actors will choose to locally optimize.

Btw, this argument about the sex ratio stabilizing at 1:1 is known as Fisher's principle. Fisher made another really interesting observation about how extremely exaggerated male ornamentation, like in peacocks, reaches its equilibrium when the aesthetic advantages from a large, attractive tail becomes offset by the practical costs of being slower, needing more food to produce said tail, being highly visible, etc. This one's called "Fisherian Runaway". These purely aesthetic traits will "run away" all the way up until they becoming detrimental to survival.

[mpalczewski]

Thanks for the correction, yes that's what I meant.

[jvanderbot]

The momentary blip of availability of sperm donors, moral acceptance, combined with eventually-to-be-figured-out reduction in overall fertility will probably have zero effect on our evolutionary trajectory.

[daniel-cussen]

> Think ghengis khan except on a smaller scale.

Possibly not on a smaller scale. The man with the most children was a ruler of Morocco with 888, and there was a guy breaking into sperm banks to replace the sperm of astronauts, neurosurgeons and all the rest with his own. He apparently sired over 600 children.

[Bjorkbat]

I don't think an increase in sperm donor activity will necessarily make much of a dent. The growing demands of industrial society and the perceived diminishing value of having a family compared to life's other pleasures won't be so easily resolved through readily available sperm.

On that note though, perhaps relationships might be less common. Who knows, maybe we'll turn into bears.

Got a chuckle out of the Genghis Khan comparison. If I was an archer on a rampart, and I saw one of these guys on horseback dressed in Mongol armor, I'd probably laugh so hard that I'd fall right off the wall.