Many couples have 4 or 5 kids, but it is unusual for a couple to have 10 or 15. Shouldn’t humans have evolved to want as many kids as possible to maximize the chances that their genes are passed down?

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    $\begingroup$ Remember that until 100 years ago even in developed countries, conditions were very different than now -- women often died in or near childbirth, children often died of disease during childhood, hormonal birth control was not available, etc. $\endgroup$
    – Armand
    Aug 14 '21 at 21:35
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    $\begingroup$ Because many humans are intelligent creatures. and place their personal well-being ahead of abstracts like evolution? I mean, why on Earth would I give a damn about whether or not my genes are passed on? $\endgroup$
    – jamesqf
    Aug 15 '21 at 16:32
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    $\begingroup$ There's strong cultural component to it. It is not uncommon in strongly religious communities to make as many children as possible. Also, baby-boom took place not so long ago, while average number of children in a modern European family is 1-2 (depending on the country). $\endgroup$ Aug 17 '21 at 15:32

Typical family sizes (especially in developed countries) are much smaller than they used to be, because cultural factors influence behaviour (do you want to have 10-15 kids if you can't afford to give them a good education?) From Kopf and Livni 2017:

The number of her own children currently in a 40-year-old woman's household, 1850 - 2015

More fundamentally, maximizing the number of offspring does not necessarily maximize reproductive fitness, because the amount of resources/care you give to each individual offspring matters; if you have too many offspring, maybe none of them will grow up to be high-quality/reproductively successful. This trade-off affects non-human organisms as well; there is an entire literature in evolutionary biology on optimal reproductive tactics that includes this issue (Pianka 2008).

Kopf, Ephrat, and Dan Livni. “The Decline of the Large US Family, in Charts.” Quartz, 2017. https://qz.com/1099800/average-size-of-a-us-family-from-1850-to-the-present/.

Pianka, E. R. “Optimal Reproductive Tactics.” In Encyclopedia of Ecology, edited by Sven Erik Jørgensen and Brian D. Fath, 2567–72. Oxford: Academic Press, 2008. https://doi.org/10.1016/B978-008045405-4.00841-7.

  • $\begingroup$ Wow. Great answer, thanks! $\endgroup$
    – The Mamba
    Aug 14 '21 at 21:16

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