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This is a curious book that explores the evolution of beauty in tropical birds, such as Manakins and Bowerbirds, and then applies the generalizations observed in birds to human evolution. This exposition revisits classic evolutionary debates in the late 1800s between Charles Darwin and Alfred Russel Wallace. Darwin’s idea of sexual selection has been mostly ignored for a century by evolutionary theorists, who favored Wallace’s concept of explaining evolved traits in terms of adaptation to the environment. However, in 2017 Prum makes a strong case for the role of mate choice to account for many traits that are nearly impossible to explain using standard survival-of-the-fittest adaptationist arguments.

The general term for these qualities is “beauty”, but that term is defined to include not only expected qualities such as coloration, patterns, and ornamental appendages, but surprisingly some other kinds of traits, such as the ability to learn new songs that are attractive, or perhaps the ability to fly high above the forest and then dive at high speed to make specialized feathers buzz attractively in the fast flowing air, or to make a beautiful garden of colorful objects to show their refined aesthetic abilities. Prum stresses the evolution of female sexual autonomy as a factor in mate choice, which has led, for example, to the development of bowerbird structures that protect the females while enabling them to observe the male’s display traits.

These things have no noticeable direct survival value but they do have value in attracting a mate, and securing successful sexual intercourse, and thus in producing the next generation of offspring. If there is any genetic component to this form of mate selection based on perceived beauty, then it gets passed onto the next generation, and this quality is eventually propagated throughout that species or subspecies, which sometimes becomes an isolated species. When that spatial separation occurs the subspecies can develop very specific beauty specifications for mate selection.

The Evolution of Beauty by Richard O. Prum

All of this bird-brain selection for beauty stuff was fascinating to read about, but then we come to the processes for human mate selection. Prum applies the ideas he cultivated from his years of study of birds in general and tropical birds in specific to us humans. We humans like to think that we with our larger brains would be better at selecting mates. The general ideas for selection based on Prum’s broad definition of beauty seem to hold up better for describing human mate choices than the standard theories based on simple reproduction of the survivors. Recently we humans haven’t had too much of a problem surviving to reproductive age when we make our selection for mates; thus other options arise, such as social status and the various forms and measures of beauty. I have written about this in this blog under the rubric of Eveish Selection where the great number of unusual human traits have arisen because human females found these traits attractive in males. Males, on the other hand, are still primarily driven by the standard sexual selection of beauty based on physical attractiveness and health.

If you have the slightest interest in sex you will find this book fascinating.