For some species, the battle of the sexes is a fully-fledged war. Male seed beetles, for example, have penises resembling medieval torture devices.
Credit: Goran Arnqvist & Johanna Ronn
Maybe female seed beetles have their own “What the hell?!” exclamation. Even for insects, it’s difficult to imagine any other reaction to a male Callosobruchus maculates beetle’s penis, which has spikes.
“It jumps to mind as something quite dumb,” says biologist Göran Arnqvist of Uppsala University in Sweden, who for much of the past eight years has studied seed beetle sex.
Male beetles of several Callosobruchus species have sharp edges on their sperm-delivery organs. The females’ ducts grow a bit of extra toughening but not enough to make sex safe from injury. After many tests, Arnqvist has concluded that the genital excesses aren’t good for the species as a whole. These seed beetles would have less-damaging sex – and would produce more babies – if males lost their spikes.
Discussions of evolution often glorify the beautifully apt forms: orchids with nectar recesses just the right length for the tongue-like structure of a certain moth, or innocuous butterflies with the same wing colours as a poisonous neighbour. Yet the most dramatic examples of the power of evolutionary theory may come from the strange and ugly stuff — biology too stupid to have been designed.
Trying to understand counterintuitive sexual parts and habits follows in the best of scientific traditions. As Charles Darwin worked up his ideas on evolution, he pondered male phenomena that looked useless, or even harmful, for surviving. Outsized horns on male beetles puzzled him, as did male birds with gorgeous plumage.
Out of this consternation came his insight into a process he called sexual selection, which he distinguished from natural selection. There may be survival of the fittest, but there’s also survival of the sexiest.
Today the sex-related selection process doesn’t get much attention outside scientific circles, but it’s a powerful tool for making sense of downright peculiar characteristics. Arnqvist and other biologists are expanding Darwin’s framework, exploring the counterintuitive aspects of sex from flirtation to family life. And theorists are discussing female behaviour that Darwin never recognised, or perhaps just didn’t care to discuss in print.
When Darwin first put his full idea of natural selection into print, he knew it wasn’t enough. In 1859, he argued in On the Origin of Species that organisms best adapted to their environment survive in greater numbers and leave more offspring than do their less fit neighbours. Thus more suitable traits gradually replace clunkier versions.
Yet antlers on stags and tails on peacocks could hardly be adaptations to the environment. Both antlers and tails may be so familiar that it takes a minute to summon a sense of their absurdity. They’re huge. They must drain energy to produce. There’s no way they improve agility in locomotion or foraging.
“The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!” Darwin wrote in a letter to the botanist Asa Gray, albeit in a whimsical paragraph. Nauseated or not, Darwin was willing to step beyond survival of the fittest.
