According to a 2010 study from the University of Oxford, big butts result in healthy children because of the high amount of Omega 3 fatty acids (the good fatty acids) stored. These are the same fatty acids that are responsible for the normal development of the baby's brain.

But according to the Chicago Tribune, scientists have proved this a long time ago, in 2007 to be precise. They noted that women with fat-bottoms are smarter than women with flat-bottoms. Again, the reason is because of the heightened storage of Omega 3 fatty acids, which improves the functionality/development of their brain.

Evidence shows that the fat content in a mother's breast milk comes from her lower half of the body, which includes her thighs, buttocks, etc. This means that the high amount of Omega 3's becomes a part of the baby's balanced breakfast.

The high amount of Omega 3 storage could be the reason why fat-bottomed women seem attractive to men because it becomes an evolutionary way of ensuring successful children. In the words of a common man; the reason why J. Lo seems so hot to men, is because men have a biological imperative to produce intelligent offspring.

William Lassek from the University of Pittsburgh is the person who hypothesized this. He even went ahead and published a book titled "Why Women Need Fat."

But, having fat-bottoms is not the only way of having intelligent children. There are other factors that play a role in it, such as the overall fitness of your body, and the diet. The issue of unhealthy fat comes into play as well, but monitoring is easy as body fat scales show women the exact percentage of body fat they have to make sure healthy levels are not exceeded and that they stay within normal parameters.  

To conclude, stay active, stay healthy, and carry good fat below the waist, and of course, having healthy genetics doesn't hurt either.

The next study for William Lassek will undoubtedly be the biological imperative associated with an eye for blondes. But that's something we'll save for later.