Ha, Leigha what an amazing question! Obviously one you’ve thought about quite a bit!
Well, it’s probably the case that men’s nipples are a useless left-over from our evolution. Though some men can produce very small amounts of milk from them (gross!) it’s not enough to feed a child and certainly isn’t as good as mothers milk.
These kinds of pretty useless organs are known as “vestigial” organs. Our appendix and tonsils are also believed to be the same type of organs. Previously useful, but now useless.
The reason men still have nipples is probably to do with the linkage of genes and the fact that some genes cannot be separated when developing. This is called “constrained evolution”
Coming straight off the back of Shane’s answer, nipples in males are a classic example again of evolution and genetics. Because evolution favours beneficial or helpful traits, we assume everything the body has, was selected for a benefit. However evolution can also be lazy, if a trait lacks purpose, but does not cause harm either (ie a neutral effect instead of a positive/negative), evolution almost forgets about it! Hence vestigial organs like the appendix and tailbone!
So you could say, the main reason man have nipples, is because women need theirs!
Ohhh great answers guys 🙂 one last addition, men have nipples because, as an embryo, everyone is a female until the Y chromosome kicks in! Interesting hey? Only after 6-8 weeks does the Y chromosome kick in and the fetus begins developing male characteristics. By this point breast tissue, milk ducts and nipples have already formed. This happens in all mammals, the only exception being stallions, who do not have nipples. Great question!