THE EVOLUTION OF FEMALE NATES:

Sexual Selection:

Darwin argued that the remarkable shape of the human female's nates was an example of sexual selection, (which see). In short men like callipygous women and therefore mate preferentially with callipygous women.

Below is an alternative argument using natural selection not sexual selection.

Time between meals:

Women are generally smaller than men and can go without food for a shorter time than can men.

[It is not at all obvious why women can fast for the shorter period:

Smaller animals have a higher specific metabolism than larger and so burn up their food reserves faster. For this reason they must eat more food. (If smaller animals had the same metabolism per unit body weight as larger animals then there would be no difference in the times the two could go without food.) However women should have a lower, average specific metabolism than men - this is from theory, I do not know any empirically derived figures - and so should be able to starve themselves for a longer period than men. The most straightforward argument might be that women have a lower ratio of cannibalizable tissue to "vital" tissue. Thus, during a fast, they run out of those tissues which they can use as "food" faster. They get down to tissue that cannot be "eaten", because doing so would be fatal, faster. This might be due to their relative dearth of skeletal muscle.]

Humans as fasting specialists:

It is assumed here that humans are adapted to sometimes going for long periods without food, or for surviving periods when food is short. This might account for their fattyness (and in turn for their nakedness - having got a lot of fat it might as well be distributed over the body surface, in an insulating layer, making a coat of hair redundant.)

A camel's hump:

Assuming the need to survive fasts and given their ill-fitting equipment for this task women need a food store - a camel's hump. (An interesting question is why could not women simply store a hoard of food in a sack for use when necessary? However, rightly or wrongly, it is usual to ignore considerations of this kind.)

The best place for it:

The positioning of the hump on the nates and thigh backs is clearly bio-physically optimum. Placed higher a mass would require reinforcement of the spine - an evolutionary "expense". Placed lower, on the feet, say, it would be as though one were wearing lead boots - walking and running would be considerably more energetic. The characteristic rear out, chest forward posture, adopted when upright, is necessary to place the center of gravity over the feet.

Pigmies:

In African Bushmen, a race of small stature, the male is also endowed with protuberant, fatty nates. The female has these attributes in a hugely developed form and is an astonishing sight for those unused to this conformation. (It is noticeable that the media does not show pictures of pigmies, or only rarely. It is easy to suspect this is for fear of exciting too great a level of racialism for optimum social control.

The simplest way to defend the argument, against the background of pigmies, is to claim (I do not know if this is true) that the pigmy shows, in the usual way, a higher specific metabolism than larger races.

And see female.