The Evolution of Beauty

Darwin's theory of natural selection goes something like this: through the generations, the traits in an animal that help it survive are passed on--longer beaks for grabbing insects, camouflage, a long neck for eating at the tops of trees, etc. But Richard O. Prum, in his book The Evolution of Beauty, discusses a theory Darwin had that is controversial--sometimes it's just aesthetics.

Prum, an ornithologist, is one of those who poses the idea that mate choice can sometimes be based on beauty (beauty, that is, to the animal itself, not by human standards). "For example, a male may have the optimal tail length for survival (that is, favored by natural selection), but if he is not sexy enough to attract even a single mate (that is, disfavored by sexual selection), he will fail to pass on his genes to the next generation." Just what is "sexy" to a bird, though? Prum has done extensive field studies of various birds, mostly the South American manikin, and detailed the males "presentation," that is a little show they put on.

Prum's argument seems sound to this layman, but it is not universally accepted. Evolutionary biologists search for reasons of survival to account for "ornaments," such as a peacock's feathers. But, he points out, the peacock's feathers may attract a mate, but it does not help his survival, and in fact may be a hindrance to it. Prum's maxim is that "Beauty happens."

The book is for the general reader, although I admit there were parts that went way over my head. I did focus on a chapter describing the violent sexual habits of ducks--they will gang rape, which Prum points out can be detrimental to the species (some female ducks get killed). And chapters on humans will surely grab the interest of most readers, especially when discussing the male penis. You guys may be happy to know that human men have the largest penis size based on ratio to the body. A gorilla's is only about an inch and a half, a chimpanzee's three inches, while the average human penis is six inches. "Human males are notably distinct from other primates in that they lack a baculum—also called the os priapi. The baculum is the mammalian penis bone, or the bone in “boner.” As for females, humans are the only mammal that has permament enlarged breat tissue--all other species grow breasts when they are in heat or pregnant.

Prum inserts himself into the book often, which has a humanizing effect. I was amazed that while he was watching birds in Surinam a six-foot-eight telephone company worker was there on vacation, a place he repeeatedly went to. I am not a birdwatcher, but I know one, and they can be intense. As Prum notes, "I started bird-watching and studying birds at the age of ten, and I never really considered doing anything else in my life. Which is fortunate, because I am now unfit for any other sort of employment."