Lester Earnest (les at cs.stanford.edu)
In order for evolution to advance efficiently it is important for individuals of all species to select the best mate available. Various species have evolved different strategies for doing that and, as you may be aware, male birds generally try to look pretty and ruffle their feathers while doing dances to attract females. Based on these exhibitions, females then choose who to mate with.
It is interesting to note that the ancient ancestors of birds were closely related to some large dinosaurs such as Tyrannosaurus Rex and it is likely the they too used that strategy, which would have been quite a spectacle. Most likely our small mammal ancestors witnessed some of those Tyrannosaurus exhibition dances but would have had to stay out of the way in order to survive.
Humans play this game the other way around: young women try to look pretty and dance a lot. In preparation for that, little girls are genetically programmed to like to dance whereas little boys are generally more interested in wrestling, in preparation for showing their power.
After clothing was invented, women mostly wore dresses or skirts to advertise accessibility while men wore trousers, which facilitate showing their crotch bulge and they sometimes padded it a bit. Similarly, women sometimes pad their bras or get breast implants to draw attention there. Men try to show their power and based on the women they see, men generally initiate mating. In fact, powerful men often try to collect harems, like other herd animals.
In some parts of the modern world, young women have now stopped wearing skirts or dresses in favor of skin tight trousers or shorts that show a lot of anatomical details. However, it is still basically the same game.
At some point in the 1800s women prostitutes who specialized in fellatio reportedly invented lipstick as a form of advertising. However lipstick was soon taken over by women of all kinds, which indicates that calling attention to their lips made them more attractive to men. It appears to me that this is because lips are reminiscent of another interesting part of female anatomy.