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In 1860, the year after Charles Darwin had published his On the Origin of Species, he privately confessed to a colleague: ‘‘The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick!’’ It doesn’t take a genius to work out the cause of Darwin’s nausea.
Natural selection, as he had defined it, was assumed to modify the physical structure and function of a species’ composite parts, so that they were all adjusted to their environmental conditions.
Overall, it was presumed to shape an animal to make it better adapted to its life circumstances.
But how on Earth could such a theory explain something as gloriously impractical as the five-foot-long, eye-spotted upper-tail coverts of a male peacock? Far from leaving the owner skilled at negotiating its environment or better at escaping predators, this ludicrous appendage appeared to make it less able to survive. The peacock’s tail seemed the most beautiful and elegant rebuttal of Darwin’s arguments.
At least it did until, according to the author of this remarkable book, Darwin came up with the answer. It was an insight every bit as world-defining as his original theory and he described it in a later book, The Descent of Man, and Selection in Relation to Sex (1871). Darwin argued that another evolutionary force was at play among life in the way that organisms select their prospective partners. Natural selection may lead to the survival of the fittest, but sexual selection, as we now call this other mechanism, does not necessarily make a species better adapted.
Mate choices based on aesthetic criteria, of which the peacock’s tail is a perfect example, can give rise to arbitrary, even maladaptive characteristics. And not only does sexual selection lead to the acquisition of such useless adornments, it also has a co-evolutionary impact on the desires expressed by the male peacock’s mate. In short, what helps shape life on Earth is the subjective feelings that operate largely within female organisms.
According to Prum, this is Darwin’s truly ‘‘dangerous idea’’, and one that patriarchal Western scientific culture has instinctively disliked. Prum explores in detail the antagonisms that sexual selection has aroused over the 150 years since Darwin articulated the idea. While natural scientists from Alfred Russel Wallace to Richard Dawkins may have accepted its existence, they have also sought to collapse its significance and make it a subsidiary element within the general theory of natural selection.
They argue that mate choices may lead to beautiful and bizarre adornments but that these features are also ‘‘honest’’ indicators of the good genes and vigorous health possessed by their male owners.
Prum calls it the ‘‘beauty-as-utility argument’’ and characterises it as a majority view, one to which he has been a lifelong opponent. In The Evolution of Beauty he provides a detailed justification for his position, making his book both an objective description of how sexual selection operates and a form of scientific autobiography.
It also mimics Darwin’s literary output in two crucial senses. Like his great hero did, it has taken Prum decades to assemble the hoard of supportive evidence that underpins his views. He has also articulated his life’s work in prose that is as lucid as the arguments are sophisticated: Darwin couldn’t have put it better himself.
The author is a lifelong birdwatcher and many of his favourite organisms feature strongly in the array of case studies that make up a good deal of the book. But the bird family that launched Prum’s scientific journey is a group of tiny, intensely colourful Neotropical inhabitants called manakins. The males of the group perform a bizarre display that has evolved under a severe form of sexual selection that Prum describes as 54 ‘‘distinctive ‘ideals’ of beauty’’.
One of the better-known of these birds is the red-capped manakin, which performs a dance routine said to resemble Michael Jackson’s moonwalk. Another, the blue manakin, often functioning in collaborative teams of up to seven males, does a Catherine-wheel-like flutter past the dowdy female.
In their relatively long lives, as many as 90 per cent of male blue manakins may never get to mate. As Prum points out, these birds ‘‘engage in the most ruthless sexual competition known in nature’’, but it is not a violent transaction conducted with teeth and horns. Appropriately for one of Brazil’s best-known birds, it involves a song-and-dance number, of which the super-picky females are the ultimate arbiters.
What makes this book so absorbing is that Prum expands the range of his material to speculate on a panorama of intriguing questions. To give a small sense of this eclectic span, he proposes that sexual selection could have played a very important part in shaping feathers in dinosaurs and in the evolution of flight by their avian descendants, and that it may even have led to the Old Testament story of how God made Adam’s partner from a spare rib. According to Prum, the real bone used to fashion Eve may have been a baculum, a penis bone, which is found in all primates except two – spider monkeys and ourselves.
Prum devotes the last third of his book to considering how mate choices may have been decisive in shaping aspects of human physiology and behaviour. This is likely to provoke much of the attention that the book rightly deserves, because here he dwells on the size and shape of the human penis, the existence of the female orgasm and the evolution of same-sex sexual relationships, all of which are hard to explain through natural selection alone.
Prum’s thoughts on these matters are compelling stuff, but the book’s chief achievement is to challenge our relentlessly anthropocentric perspective. The Evolution of Beauty enables us to see that the most intimate emotions and subjective choices made by mere beasts are decisive subjects for science. And it is these aesthetic sensibilities, as owned and operated by other animals, that have fashioned the manifold beauties of our world.
Mark Cocker’s new book, “Our Place”, will be published in 2018 by Jonathan Cape
The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World – and Us
Richard O Prum
Doubleday, 448pp, $30
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This article appears in the 21 Jun 2017 issue of the New Statesman, The zombie PM