Commenter Keyster just linked a BBC article blaming men for women’s menopause, which is kind of a stupid premise given that evolution is shaped by environment rather than conscious preferences.

Researchers have long been puzzled as to why it appears that human are the only species where females cannot reproduce throughout their lives.

Previous theories had proposed a “grandmother effect”. This suggests that women lose their fertility at an age where they might not live to see a child grow, and instead are available to care for younger women’s children.

The menopause was therefore seen as the block to older women from continuing to reproduce.

But this latest theory suggests things work the other way around, and that it is the lack of reproduction that has given rise to menopause.

Using computer modelling, the team from McMaster’s concluded “preferential mating” was the evolutionary answer – men of all ages choosing younger women as partners.

That meant there was “no purpose” in older women continuing to be fertile.

Prof Rama Singh, an evolutionary geneticist who led the study, said men choosing younger mates were “stacking the odds” against continued fertility.

He told the BBC: “There is evidence in human history; there was always a preference for younger women.”

I think human males’ preference for younger females might be a result of our partially monogamous nature. Of course, humans are not strictly monogamous, but we are largely so. What this means is that if a man secures a mate, it’s important that he finds one with the most reproductive potential. If chances are that you’re going to be stuck with one woman, from a genetic fitness standpoint you’d be best advised to choose a younger one so you can maximize reproductive success.

If humans were mostly polygynous like many herd animals, female age wouldn’t be as important as the total number of females, because you could impregnate lots of them in a short amount of time and replicate your genes quickly without having to worry so much about their fertility down the road. For some supporting evidence, I’d point to the fact that in polygynous cultures it is common for the man’s first wife to be older than he is.

So, I propose that preference for youth could be a result of the human tendency to engage in pair-bonding and monogamous reproduction.

As for menopause, the extended childhood of humans is likely a better explanation than any other. Pygmy women hit menopause by 30, and then die before the age of 50. Pygmies are sexually mature at about 12, hitting peak fertility at 16. Modern humans hit menopause at 50, sexually mature at about 16, fertility peaks in their early 20s, and they have a lifespan of around 70. Human women seem to be designed to last about as long as it would take their last children to become fully fertile.