Breasts and Evolution
If only someone could make a nifty little program…. about whether men are really more "visual" than women, and some of the fallacies of "Evolutionary Psychology".
Puttin' on my Actual Evolutionary Biologist™ hat here.
Breasts are an example of how human anatomy & physiology have some unique and biologically bizarre features, features that contradict each other *and* contradict what evolutionary biology leads one to explect. Examples:
1) human males average larger than females -- as is expected if there is significant sexual selection on males (=females are picky, not all males reproduce)
2) human females have enlarged breasts, of a type found in no other mammal. This suggests that biologically unusual sexual selection on females is occurring. I don't think it can be to make nursing easier, Ailurophile, because my experience is that it *doesn't* -- it makes "latching on" a good deal harder than it is for droopy-chested chimps.
3) both human sexes (in most populations) have extremely exaggerated head hair, the longest hair of any mammal. This implies heavy, unbalanced sexual selection on at least one sex.
Look at it this way. You know how many other species of bird or mammals have males larger than females, but females more brightly-colored in *any* respect than males?
*None*. Zip, zero. It does not compute. Far from being explicable by trivially easy "Evolutionary Psychology" reasoning (as practiced by sociologists, ferchrissakes), human reproductive biology is really problematic.
This is why I'm starting to think that self-domestication may be the missing link in human evolution. It's probable that for a long time (at least 100,000 years) humans have been attempting to control each other's reproduction, via arranged marriages and the like. No-one's done the math yet, so this is really just an educated guess on my part.
growth of the breast isn’t to encourage group survival, but is a result of sexual competition - females with bigger breasts had an advantage over their flatter sisters, suggesting (again) that males favoured them for whatever reason. Evo psych rears its ugly head again.And again, this is why I talk about “evo-psycho”, because they don’t actually understand biology.
For female mammals to have elaborate, permanent display structures like breasts is *bizarre*, even unprecedented (the role & significance of the sexual swellings in female baboons is hotly debated). It’s particularly weird when you recall that a woman’s breasts swell while she’s nursing — *and thus infertile*.
Frankly, I don’t know why human females have “display breasts”. One thing I would definitely ask is, who are they displaying *to*? Potential mates, or potential in-laws? Or other females?
 In most warm-blooded animals males are larger and less camouflaged than females. There are some groups in which females are larger: baleen whales, birds of prey, and rabbits, for instance. In most of these, the males are still less camouflaged (e.g. Kestrels), so sexual selection is probably still acting on males, but ecological forces make them smaller.
There are a few birds in which females are larger and more brightly-colored than males (e.g. Phalaropes), and in these species females are polyandrous -- that is, sexual selection is for once acting more strongly on them than on the males.
There are *no* species in which males are larger and females are less camouflagued.