Well, sure they can. After all, we're mammals. As such, one of our distinguishing traits is the formation of mammary glands to produce milk for our offspring. In fact, most people -- man, woman, birth mom, adopted mom and so on -- have the right equipment to breastfeed.
What is that equipment? The aforementioned all-important mammary glands (along with their requisite network of ducts to the nipple) and the pituitary gland are the two keys to making you a milk man, according to Mental Floss. The pituitary gland oversees the release of prolactin, the hormone responsible for milk production and letdown that men and women both have.
So what's the holdup, guys? A lack of stimulation, for one. Plus the fact that evolution hasn't been known to look to favorably on male animals who nurse. After all, aside from all those monogamous men and women out there, the rest of nature tends to mate like rabbits. And most male animals don't stick around to nurse progeny who may or may not be their own.
But male lactation in humans is alive and well. Don't believe me? History is rife with examples, but here's one of the most intriguing ones I dug up in an article written by the biologists Thomas H. Kunz and David J. Hosken. At the end of World War II, numerous malnourished men were released from prisoner-of-war camps. The prisoners obviously weren't in the best of health and were suffering from liver, testicular and pituitary damage, among other injuries. Once these guys started eating after their release, it threw their hormones out of whack and -- voila -- they began lactating. If you want more recent examples, read Laura Shanley's article "Milkmen: Fathers Who Breastfeed." Or check out a few pro overmuscled wrestler types.
Presumably, men could induce lactation in less extreme circumstances, but the question is, how many would want to?