Why is it that men have nipples?

Question

Also, Is it strictly human males which have nipples, or do other species have males with nipples?

Answer 1

"[A]s embryos men and women have similar tissues and body parts. If anything the embryo follows a 'female template'. That is why nipples are present in both sexes. It is the effect of the genes, the Y chromosome and the hormone testosterone that brings about the changes and masculinises the embryo. Testosterone promotes the growth of the p***s and testicles. Because nipples are there before this process begins the nipples stay!"