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Old 06-24-2016, 02:47 AM
Carl Pham Carl Pham is offline
Join Date: Nov 2010
Posts: 298
Because they can. You're misunderstanding genetics. Natural variation through random mutation will generally cause individuals to have quite significantly varying features, particularly for such simple characteristics as size. What natural selection generally does is rein in these variations, when they compromise some aspect of function that impacts survivability and breeding success. Hence, features of our genome that are absolutely mission-critical, e.g. certain basic enzymes for respiration, are exceedingly well conserved. No one has the slightest variation in them. Similarly, the size, shape and structure of the heart or airway or spinal cord is very consistent, since nearly any experiment along different lines is promptly fatal. In short, what needs evolutionary explanation in terms of functionality is uniformity of features, not variation. Variation is natural. Uniformity is not.

Breasts can vary in size wildly with essentially no impact on survivability. Furthermore, the existence of wide variation also implies that variation has almost no impact on breeding success, either (otherwise there would be selection for some optimal size). Which implies, as one might guess, that a woman's breeding success is not significantly impacted by her breast size, within a wide range. In short, there's a good supply of men who like them in almost any ordinary size.

By the way, an interesting side note on this is that breast size varies much more interwoman than intrawoman. That is, a woman may have big or small knockers, but her right is likely very close in size to her left. That actually needs explaining. Why the symmetry? It could be there is a significant hit on survivability (unlikely) or breeding success (seems more reasonable) with significant asymmetry. There is a general argument that humans are unusually sensitive to asymmetry and consider it ugly. I don't think anyone has a good argument for why that would be, though.

But it's also possible this occurs accidentally, e.g. that the same kinds of mechanisms control breast symmetry as control, for example, leg symmetry, which is clearly required for survivability. Hence the breasts are symmetric as an accidental side-effect of more essential symmetry, e.g. in limb size. But on the other hand, the human body has nontrivial asymmetry, e.g. in its internal organs, so why would symmetry of the breasts be a natural consequence of essential symmetry, when for example the lungs aren't bound by it? If development mechanisms allow the lungs and neural circuitry to be asymmetrical, why do they not allow for significant asymmetry in boobs? It may indeed come back to the possible preference we have for breeding partners that look very symmetrical on the outside (we can see whether her nipples are on a perfect horizontal, but we can't tell her liver is tremendously lopsided, so the liver is free to vary and seek some more optimal shape and location, while the nipples cannot).