Here's a really far-fetched, entertaining, unproveable (but maybe DISprovable!) theory I've been mulling over:
Point #1: Large breasts may be superfluous in women. (source: The Third Chimpanzee by Pulitzer-Prize winner, Jared Diamond). Chimps and some other mammals can nurse young fine with practically flat chests. According to him, therefore, breast size (and penis length by the way) is probably due to sexual selection and preference, rather than survival needs.
Point #2: Men rarely get breast cancer due to so little breast tissue. (source: I don't know, I read it somewhere a while back.)
Point #3: I'm suffering from a painful cyst in my (ahem ) breast. (I know! Too much information!!)
Possible conclusion: if it hadn't been for great-great-great (squared!) grandpa some 40,000 or more years ago favoring "hooters" on women, then I wouldn't have these superfluous mounds that are prone to lumps, cysts, and cancer!!
Presented in a humorous and jovial way for your reading pleasure,