Q: Ever since the recent birth of my son, who I breastfeed, I have wondered why men have nipples.
A: Many suggestions for this phenomenon have been offered. They may exist to help men check that their vests are on straight, or be present as a safety feature 鈥� to warn us how far out from the beach we can safely wade.
However, there is a more plausible explanation. Male and female human embryos are identical in the early stages of their development. If the fetus receives a Y chromosome from its father, a hormonal signal is produced: the labia fuse to form a scrotum, the gonads develop as testicles and a male results. Otherwise the 鈥渄efault鈥� female remains.
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Various structures in the adult reflect the symmetry of male and female and their common embryonic source. Men have nipples because they have already begun to develop when the 鈥渟witch to male鈥� signal is received. The development of breasts is halted in most 鈥� but not all 鈥� cases but the nipples are not reabsorbed.
Another effect of these developmental pathways which are shared by both males and females is pointed out in Stephen Jay Gould鈥檚 essay 鈥淢ale Nipples and Clitoral Ripples鈥� (which can be found in the new Penguin 60th anniversary collection, Adam鈥檚 Navel). Males need plenty of blood vessels and nerve endings in their penises to achieve erections. Because the penis and clitoris have their origins in the same structure, females have the same number of blood vessels and nerve endings packed into a much smaller area, resulting in the enhanced sensitivity of the clitoris.
Conclusive evidence that God is not a man?