>>19717202They are three different things. Take a look at pic related. Notice how it's got a really long tail? That was a result of females choosing males with long tails because they found it attractive. So why isn't it even longer then I hear you ask? Because natural selection determined that having an even longer tail was bad because it most likely was too hard to carry e.g. made it easier to be caught by predators, not metabolically favourable, made it harder to fly, etc. In other words mother nature herself finally stepped in and told the females to shut the fuck up with their preferences.
Eugenics on the other hand is different from sexual selection because it also removes female choice too. For example under sexual selection, short women desire tall men for whatever reason e.g. more attractive offspring. Eugenics however would forbid short women from reproducing with tall men if height was the trait being arbitrarily selected; the women would not be able to choose.
