Why do men have nipples?

I have noticed that men have nipples. And I have seen women do on big lumps for babies I guess for milk? But why do men have them???? is it a back up system for something?

Babies inherit one gene from their mother and one from their father. At that point, the body parts that make up all males and females are the essentially the same except for the XY gender determination. The differences in males and females come from how the body develops after conception. In females, breasts enlarge, a uterus and vagina develops. In males it becomes a penis and scrotum instead. Nipples on a male are leftover parts from that process.

There's an old farmer's expression used to describe something for which there's no purpose: "Useless as tits on a boar hog." "Useless as nipples on a male's chest" would work as well. :-)

Depending on the man, they are also erogenous zones...

Think how bare a man's chest would look without them.