So human males have nipples as some kind of evolutionary relic, right?
So do other primates, but what about the other mammals: which groups have male nipples and which don’t?
We tried checking dogs when this question came up at a party, and it appeared the dog didn’t have any, but was very afraid of us :eek:
Someone said that male horses don’t have 'em.
Where were the male nipples lost and/or regained? Any ideas why?
What makes you think they are an evolutionary relic? They are just a bit that doesn’t function in mammals that develop as a male the same as they would in a female. If you can’t find nipples on male mammals you aren’t looking very hard.
no cites but i believe they arent 100% useless, males have been known to lactate, cases were around in prison camps in WWII soemthing to do with malnutrtion but lactation none the less.
Ive never really gotten curious enough to turn every mamel i encounter upside down, but know dogs do not have them.
Wanna bet?
Well, you know wrong. I have a male dog in my house right now and I know for a fact that he has nipples.
maybe its restricted to bread, my Australian Terrior and labrador do not. Are they simply freaks?
They have them. They’re going to be very small and almost invisible, especially if the animals have thick belly fur. If you know where to look, you’ll find them.
To be honest, I am very glad I do not know where to look :D. I willt ake you word for it
Male rats do have nipples, male mice do not (they degenerate during fetal growth). Go figure.
This is always a fun question. You’re right. Male horses don’t have nipples, but it’s because female horses have their nipples between their hind legs, and in males, that real estate is used for other purposes.
So male horses lost their nipples because there was a reason to lose them. Human males have nipples because there is no compelling reason to get rid of them, and some would say they’re even kinda fun.
Instances of males lactating are usually due to large amounts of estrogen in the body, which basically feminizes them. I don’t think there’s any evidence that men, way back in time, ever actually breast fed their young.
As I understand it, male nipples aren’t vestigial breasts. Rather, the basic human body template just comes with nipples, and it’s your XX or XY chromosomes that determine how they develop.
Our yellow lab and golden retriever both have 'em. They’re hard to find, but they’re there.
People persist in imagining that evolution is some sort of conscious force making decisions, and every decision ought to have a justification. This is not the case - and why should they go away? So males have no particular purpose for nipples - they’re not harming anything, are they? It’s easier to start with one basic template and just turn parts on and off as needed. Breast growth is caused by hormones secreted around puberty - so it makes sense that breastwise, immature humans of both sexes look the same.
And for what it’s worth, I’ve heard anecdotal tales of men who, due to the lack of female caregivers in ‘primitive’ areas without baby formula, were able to eventually breastfeed babies, mostly by allowing them to suckle. I imagine this stimulus lead to the release of hormones that stimulate lactation (according to what I’ve read, the guys developed breasts.)
Oh, and my male cats have nipples - and they’re about as prominent as the females’, due no doubt to the fact that they’re all fixed.
Thanks all for your replies. 
So far we’ve got:
Male dogs, cats, and rats have nipples.
Male mice and horses don’t - the horses probably due to ahem greater real estate values in a scenic area that have encouraged development. 
Other mammals that lack male nipples?
What about elephants?
Is there any pattern of mammalian lineages with male nipples vs. those without?
Male platypodes (or platypuses) and echidnas lack nipples, but then, so do female monotremes as well.
And all marsupials, as well, if I’m not mistaken.
I don’t know about males, but female marsupials have nipples in their pouches. (Not sure if you were referencing males or females.)
How do platypodes and echidnas feed their young? I know they’re not typical mammals, but how does breastfeeding work without nipples?
Monotremes don’t “breastfeed” at all. The milk glands secrete milk onto the fur, and the young lick it off.
Monotremes have mammary glands, but they don’t have “breasts” per se.
From here
Similarly for echidnas.