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Asked by countxjackular to Austin, Kirsty, Nicola, Nike, Sarah on 18 Jun 2012.
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Austin Elliott answered on 18 Jun 2012:
There’s an answer to this one over at Scientific American, written a few years ago by a Prof of Biology.
It’s a bit technical, but one answer is ‘because women do’. Men and women share most of their genetics, apart from the Y chromosome, so males and females share most genetic-based traits – and there’s never been an advantage to men evolving NOT to have nipples. So the ‘default setting’ for a human, male or female, is to have nipples.
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Kirsty Ross answered on 19 Jun 2012:
During pregnancy, male and female fetuses develop in a very similar way through the early stages of the pregnancy. Without the contribution of the Y chromosome, the fetus will become a female, with breast tissue, nipples and female genitals. With a Y chromosome, the male hormone testosterone is released around week 16 and restricts breast development to just nipples and develops the male genitalia rather than female. This isn’t done without a fight and male babies are often slightly weaker at birth, leading to slightly higher death rate for male babies.
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