UPDATE: See the clarifications and corrections from Markus Jokela, the author of the original research cited in the Times Online article.
The evolutionary power behind this is straightforward: more attractive women tend to have greater numbers of children, and the most attractive are less likely to have sons.
In a study released last week, Markus Jokela, a researcher at the University of Helsinki, found beautiful women had up to 16% more children than their plainer counterparts.
One finding was that women were generally regarded by both sexes as more aesthetically appealing than men. The other was that the most attractive parents were 26% less likely to have sons.
Physical appearance is highly heritable, so it follows that the daughter of an attractive woman will have greater odds of being attractive herself and thus carry a reproductive advantage.
However, what about the men?
“For women, looks are much less important in a man than his ability to look after her when she is pregnant and nursing, periods when women are vulnerable to predators. Historically this has meant rich men tend to have more wives and many children. So the pressure is on men to be successful.”
As with many human traits, such as skin color or height, the distribution follows a bell curve. A shift in the curve as indicated by this research means that a comparison of two women who are average for their respective times, would place the more modern woman as the more attractive one.
A factor acting as a brake on overall attractiveness is male appearance. For example, an attractive woman may have children with an attractive man but their daughter may look like the father and therefore have an unattractive, masculine appearance. Other similar scenarios are why the majority of people are neither very attractive or very ugly, but somewhere in between.