Survival of the Prettiest: Why Did the Peacock's Tail Make Darwin "Sick"? Because the World Is Full of Extravagant Beauty That Natural Selection Struggles to Explain
Rothenberg, David, New Statesman (1996)
Popular commentators on evolution, such as Richard Dawkins, have become overly enamoured with the idea of the gene. Genetics is certainly the most powerful mechanism of evolution and was unknown in Charles Darwin's time but although we have learned much from sequencing DNA, the idea of the gene does not explain everything about the living world and certainly not about the human world. However, just as Herbert Spencer used the notion of the "survival of the fittest" to explain why some people are rich and others are poor, so Dawkins argues that culture has genes, too - self-replicating particles of information that he calls "memes" (think of the dumb jokes and "viral" videos that proliferate on the internet).
If all evolution happens for the sake of proliferating selfish genes, then everything we see in living creatures has to be useful and practical. But that's not at all how Darwin saw it. He envisioned as at least two distinct processes: natural selection and sexual selection. The former concerns the survival of the fittest. The latter, however, is an aspect of evolution that is too often overlooked today.
After writing On the Origin of Species, Darwin was perplexed by the marvellous phenomena that natural selection could not easily explain. "The peacock's tail," he wrote in a letter to his colleague Asa Gray, "whenever I gaze at it, makes me sick." Did he not appreciate the splendour of such feathered beauty? On the contrary - he just could not justify it as a useful or adaptive trait. Many of the features of living creatures caused a similar queasiness in him: long, complex bird songs, garish patterning such as zebra stripes and the elaborate artworks created by bowerbirds in New Guinea (sculptures made out of twigs and branches, decorated with carefully arranged piles of flower petals, snail shells and dried-up insect larvae) - what practical use could any of this behaviour have?
Such wondrous aspects of animals' lives need not be seen as merely useful. Darwin's second major book, The Descent of Man, dealt with sexual selection. Over hundreds of pages he catalogued those features of living creatures, usually but not always males, that evolved simply because females happened to prefer them. The peacock's tail evolved because peahens found it beautiful, and generation after generation the more beautiful display won out. In most species such ornament is tempered by practical constraints, but in this one, the females ended up wanting the male with the most extravagant and magnificent display.
You could call this process aesthetic selection. We see it all around us and it is an aspect of evolution that most people find genuinely fascinating, though they are often disappointed to discover that scientists have tried to downplay its significance. How can science best deal with things that seem impractical? Take the elegantly-designed feathers of the waxwing, the huge unicorn-like tooth of the narwhal or the outsized antlers of the now-extinct Irish elk - there's no practical reason for these features to have evolved. Inside the brains of the female animals who selected for these traits lies a definite sense of aesthetics that serves to define such features in the species over thousands of generations. Where animals appear outlandish or do peculiar things such as singing 24-hour-long songs in the case of humpback whales, or building complicated works of art in the case of bowerbirds, sexual selection can be the explanation. Evolved traits need not always be useful.
The standard view of sexual selection among Darwinians today has moved far away from what Darwin intended. For nearly a hundred years, science avoided taking sexual selection seriously, perhaps because it was embraced enthusiastically by nature writers such as Wilhelm Bolsche. Consider this passage from his book Love Life in Nature (1898):
An animal is as if bewitched during loving- time. …