The Science of Attraction

Sexual Selection

It takes 200 brilliantly colored tail feathers for the amorous peacock to even begin to impress the ladies. Females prefer the male displaying the greatest number of “eye-spots” on his train. Evolutionarily speaking, one might say that he’s only got eyes for her.

Green Peafowl (Pavo muticus), Hai Hong Karni, Thailand (2011). Photo by JJ Harrison.
The concept of sexual selection was introduced by Charles Darwin in his ground-breaking book, The Descent of Man, and Selection in Relation to Sex (1871). Among living things that reproduce sexually, evolution is determined by two related processes: competition and choice. Almost exclusively, it is the males of a species who compete with one another for the right to mate with females. Females in turn choose which males they will mate with based on whom they determine to be the “fittest” competitors. Ultimately, female preference for certain male traits ensures that these are passed down to their offspring and subsequent generations. This often promotes the evolution of exaggerated characteristics in males – the magnificent tail of the peacock, for instance – which readily distinguish them from females of the same species.

Peafowl displaying to peahen. Warwick Castle, England (2003). Photo by ToastyKen.
In Jackson’s chameleons, only males have horns (female in background).
Photo by Javier Alvarez.