Darwin introduced the idea of sexual selection as a complementary to natural selection. In the living world, one sex, usually the female, invests more in reproduction process. She has standards to choose the best males to mate with. On the other hand, males can mate with many females. In order to spread one’s own genes as many as possible, the males compete with each other based on females’ standards in order to win the chance to mate with females.
The picture above shows two male red deers competing with each other. They are trying to show their strength and fitness to attract female. Some female doesn’t choose male based on the strength. For example, peacock. The male peacock that has the most beautiful and incredible tail always attracts a female peacock. Such selection has no apparent relationship with fitness, but “ornaments”. By selecting peacock with beautiful tails, a female will have “sexy sons”, who can pass on her genes in the future.
So, has sexual selection influenced the evolution of human? Although there’s not so many academic research to prove it, but it will be doubtful to say no. Some scientists have suggested that our brains are the result of sexual selection. Our ancestors viewed intelligence as one of the standards while selecting partners to mate with, so that we become smarter and smarter during the evolution.