Asked by: Lisa Milne (age 14), Oxford
They have evolved separately, which is why the two sexes are physically different.
Evolution has favoured men who have lots of children, so their biological contribution to reproduction is just a few millilitres of cheaply produced sperm. Women, on the other hand, need to supply literally all the energy and nutrients required to build a baby from scratch and feed it, so they’ve evolved a uterus, placenta and milk-producing breasts.
However, there is a limit to how far the sexes can diverge. Men and women only differ by one chromosome – the Y chromosome – and all the physical and hormonal differences between the sexes ultimately have to fit into that one chromosome.
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