You are missing it, failing to 'get it', running off in unnecessary directions, and flailing away at irrelevancies. It's simple, dirt simple: Here the shortes

You are missing it, failing to 'get it', running off in unnecessary directions, and flailing away at irrelevancies. It's simple, dirt simple: Here the shortest clear explanation: "The hand the rocks the cradle rules the world.". If you don't like that one, take all the woman in the US at, say, 18. Put each woman into either (A) REALLY wants to have children and be a good mommy and is concentrating on finding a suitable husband and (B) women with less overt interest in being a mommy. Then, track (A) and (B) over a few generations and see what happens. Is there any doubt in your mind? The women in (A) will have the strong limbs on the tree, and the women in (B) will have weak, sick, or dead limbs on the tree. Then over time, the fraction of women in (A) will increase, and the fraction of women in (B) will decrease. In particular, genes that put women into (A) will increase. Just what is it about this 'thought experiment' you find difficult to understand? Here is what should be your first question: Q. If this thought experiment is correct, then why do we have any women in (B) now? A. I should leave the answer as an exercise. Here's one piece of historical evidence: Supposedly in year 1800 could take all the women in the US of Western European descent, track their descendants, and by year 1850 discover that their population (of say, just the women) had increased by a factor of four. We're talking 50 years with nearly all the women pregnant nearly all the time. So, (A) or (B) didn't matter: Due to very strong social, economic, and practical pressures, the women got married, and then the babies 'just came'. Since then, more and more, (A) and (B) mattered a LOT. So, now women in (B) have the option of concentrating less on motherhood and do and, thus, are pulling their genes out of the gene pool. In a few more generations, what stands to be left is women in (A). The effect of (B) is already strong and easy to see: In the more industrialized countries, women of Western European descent are having way less than 2.1 children per woman and, thus, are dying out. So, as women in (B) die out, the population can continue to shrink. When about all that is left is women in (A), then the population will stand to increase again. Come back in 100 years and find a LOT of REALLY eager women in (A)! Your next question should be: Q. But women in (B) should have reproductive advantage because of their better ability to contribute to the economic strength of the home. A. Good point, but so far it's not working. I suspect that somehow it won't work well enough before the women in (B) die out. Complicated it's NOT.