Why do men have nipples?

Many great thinkers have pondered this -- even Aristotle had a crack at answering the conundrum!

The answer is that in the first few weeks of development in the womb, male and female embryos look exactly the same.

Every embryo has the potential to be either male or female -- the determining factor is the chromosomes that it carries. Chromosomes are like little packs of instructions which determine aspects of the development of an embryo, including its sex. The male embryo has an X and a Y chromosome and the female has two X chromosomes.