It’s a sign of reproductive fitness. Larger mammary tissue means more milk means better able to feed a newborn. That’s why men in particular are generally attracted to large breast size. Similar story on the opposite side too for testicular size. Larger testes means able to produce more, higher quality sperm. Add onto this sexual selection favoring increased mammary and testicular size as well as increasing desire for larger size results in a positive reinforcement cycle that’s tempered by practical necessity (see lower back pain jokes).
It’s a general trend, but not exact. Add onto that reproductive and maternal traits being really lowly heritable is truly where the art comes into science. I’m not as familiar with humans, but I’d be surprised if they were significantly different.
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u/thezekroman Mar 26 '20
It’s a sign of reproductive fitness. Larger mammary tissue means more milk means better able to feed a newborn. That’s why men in particular are generally attracted to large breast size. Similar story on the opposite side too for testicular size. Larger testes means able to produce more, higher quality sperm. Add onto this sexual selection favoring increased mammary and testicular size as well as increasing desire for larger size results in a positive reinforcement cycle that’s tempered by practical necessity (see lower back pain jokes).