The two theories, survival of the fittest and of the sexiest have both been invalidated in large
part by medical science and society. In a primative society the fittest would be more likely to survive and
reproduce but with our medical science even the poorest specimen has a good chance of surviving and of reproducing.
In fact, the poorer specimens are often times reproducing at a rate greater than the better ones. You could argue
that medical science is leading to a general degradation of the human species by making it possible for more, less
physically and mentally developed people to reproduce and survive.
The better looking people in a primative
society probably were able to reproduce more often but in our society where fidelity is mandated by government
regulation, the churches and public mores you see a stratification rather than a lack of reproduction. In other
words, the most attractive people are generally going to mate with one another while the less so will do the same.