The tuned tail of the peacock has kept many evolutionists up at night and has come to symbolize the consideration of “expensive” ornaments in the natural world. Are they evidence of strength or evidence of handicap?
In 1860, Charles Darwin wrote: “the sight of the feathers in a peacock’s tail, whenever I look at them, makes me nauseous.” The British naturalist, one of the fathers of the theory of evolution, meant that the origin of the peacock’s tail is difficult to explain if we focus on utility or natural selection understood as a path to fitness. And indeed, while traits such as speed, strength, or endurance are easy to interpret in the vein of the classical arms race, the expensive, bulky, and bright tail escapes a simplistic understanding of evolutionary relationships. And very well, because this simplistic understanding of the processes that shape life on Earth is incomplete, and in many contexts downright wrong.
Darwin himself also realized this, and a few years after his confession about the peacock’s tail, he published The Descent of Man, and Selection in Relation to Sex, in which he collected his observations concerning, among other things, the mechanisms of sexual selection. In so doing, he came closer to understanding the origins and meaningfulness of features such as the tuned peacock tail. However, he certainly did not settle the key issues once and for all. The conversation about “flashy accessories,” risky behaviors, and seemingly impractical solutions in nature was just gaining momentum. A pace that continues to drive the discussion today.
The handicapping hypothesis
Examples of “unnecessary” costly traits and behaviors in the animal world that researchers have been puzzling over for decades go well beyond the peacock’s tail. They include, for example, the antlers of deer (which, after all, are heavy, slowing down the run and making escape difficult), birdsong (exposing location, attracting the attention of predators), or bright coloration (making it impossible to go unnoticed). All of these features seem to reduce the chance of survival. Also because they are expensive in terms of…