Found in 2 comments on Hacker News
defen · 2009-05-19
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I couldn't find a good pithy blog post explaining it, so instead I'll direct you to a couple things I did find. I first read about it here (search for 'cave'): http://www.arthurdevany.com/2005/06/weepy_relatives.html
Which led me to Randolph Nesse: http://www-personal.umich.edu/~nesse/ who wrote this book: http://www.amazon.com/Why-We-Get-Sick-Darwinian/dp/067974674...
There are several chapters about the hormonal effects of childbearing and what the evolutionary benefits are for the children. A few i can remember off the top of my head are:
Breastfeeding will often prevent women from ovulating and thus becoming pregnant. In this way mothers resources are not strained by taking care of too many children at a time and the current child will have a better chance of survival.
Fetuses secrete a hormone called human placental lactogen that inhibits maternal insulin, this leads to high glucose levels in the blood and thus more nutrients available to the fetus it can also result in diabetes in the mother during the pregnancy.
preeclampsia (gestational high blood pressure) is another similar effect where hormones excreted by the fetus raise maternal blood pressure in order to increase blood flow to the placenta.
Having a fathers testosterone levels fall during early parenting is probably a key evolutionary adaptation because it would prevent fathers from seeking new mates (in order to make more babies and thus spread their genes) in order to care for the new child. The study noted that testosterone levels later rose when the children became older, this too follows the evolutionary argument because once a child is old enough it is more efficient for the father to attempt to father more children.
By far the most interesting part of this section in the book was about male jealousy. The theory is that because it is fairly difficult for a man to tell whether or not he is raising another mans child. men have evolved to be overly protective of their chosen mates so that they do not invest to many resources (time included) and thus lower their own genetic viability. Jealousy, while present in both sexes is a much stronger emotion in men (according to the authors this is true across all cultures).