My understanding is that it's called the Elbow Setting Angle. There's a noticeable difference between men and women as to the angle that the angle that the elbow bends to, when the arm is at maximum extension. The reason is believed to be a simple one: hang your angles straight by your sides with the palms open and facing backwards. Press you elbows in as far as they will go. To point out the obvious, since women's hips are bigger, they need to be able to bring the elbow in further before it touches their sides, and thus their arm bends further back. The only mystery is: why on earth this is an evolutionary pressure.
M