My very first contribution to the collected sum of human knowledge has just been published in the Journal of Evolutionary Biology. The paper is called: “A Dynamic Framework for the Study of Optimal Birth Intervals Reveals the Importance of Sibling Competition and Mortality Risks” and you can read it online or download a PDF. I’ll talk about the main results in this post.
The egg that eventually became you once lay in your grandmother. This giddy fact(oid) happens because, in the womb, women develop all the eggs they will ever use. The supply gradually declines through the years to the point where no more eggs remain, no more children can be sired: menopause.
But why should fertility grind to a halt several decades before the body gives out? Why lose the ability to reproduce? If life is all about making babies and turning them into baby-making machines themselves (speaking biologically, not philosophically), why run out of eggs but carry on living?
From birth, all the eggs a woman will ever get are stored in her ovaries. Her stock of eggs diminishes throughout life – some mature during ovulation, while others die as a kind of collateral damage, spurring the process along. Her cache dwindles until too few eggs remain to maintain fertility. This point is menopause and it is inevitable.