Originally Posted by zinc
I'm a bit suspicious that the required infanticide to allow the group to migrate around (can't do that with piles of babies and toddlers!) eventually created the pressure to switch to agriculture. Just idle speculation but it would seem there would eventually be anti-infanticide pressure, and the solution would be "don't travel around", leading to agriculture.
Don't assume that all that fucking always resulted in pregnancies. I am sure the mothers nursed their children much longer than many modern mothers do today. You can nurse a child for two years, five years, whatever - it's natural birth control, and enables a few years' spacing between offspring. Many native cultures still do this intuitively. The prevalence of children born close together began when birth control (which has always been around) became a sin, and later when it became fashionable to use formula, and wean babies after just a few months.