Hi Jeanie

Sexual selection is a well known characteristic of evolutionary theory. In this scheme mates are selected for based on secondary characteristics which are usually indicators of fitness. An obvious example would be peacocks tails. The size and colour of the males tail is used by the hen’s as an indicator of the males fitness so larger and brighter tailed males are chosen more often as mates. How this works for evolution is really pretty simple. Tail size is a variable trait, some males have larger tails some smaller and of course fitness is also variable. Having a small tail makes life easier, they are not so heavy to carry around and they don’t stand out to predators as much so you don’t have to be a particularly fit male to do well with a small tail. For large tailed males the story is quite different, while fit and unfit alike will sometimes have large tails the unfit individuals are more likely to be eaten or to starve in lean years than the really fit males so on average a larger tailed male is going to be a fitter one by virtue of the fact that he has managed to survive and thrive having such an impediment attached to his rear end. Further the brightness of the tail attracts predators but it too is an indicator of good diet as hungry males don’t have the energy to create bright colourful tails while surviving with a bright colourful tail also shows your fittness. So the characteristic selected for by the hen’s is not fitness but it is a reasonable proxy for it. As for pale skin as opposed to dark skin in humans there may well be something similar going on though I’ve never really thought about the ins and outs of it.

All the best Jeanie

Russell