Survival of the Weakest
If “sometimes it pays to be a weakling,” what does that mean for 154 years of Darwinian teaching about survival of the fittest? What does it mean, further, when sexual selection doesn’t work?
Natural selection works, except when it doesn’t: Science Now teased with the shocking headline, “Sometimes it pays to be a weakling.” The article discussed rams and their big horns. Decades of study are now showing that while the rams with the biggest horns tend to win mates, they die younger; the weaker ones with stubby horns have enough offspring to maintain their genes in the population. So there’s a tradeoff; “Horn length has opposite effects on reproduction and survival,” one author of a new study explained. This tradeoff affects more than just sheep:
Pondering the peacock’s elaborate plumage, the father of evolutionary biology, Charles Darwin, proposed that the drive for sex—and for producing offspring—was a powerful force in evolution. Fending off potential rivals or vying for a female’s attention has driven males to be ever more extreme—bigger, stronger, more colorful. This process, called sexual selection, should also affect the genes, so that only versions of genes that lead to these enhanced qualities should exist. But this isn’t what happens in the real world. There are plenty of small, weak males among the supermen.
Sexual selection works, except when it doesn’t: Another article on Science Now cuts away at the other “selection” pillar of Darwinism, sexual selection. “Forget plumage; birds sniff out good mates,” the headline shouts. As shown in a previous article, female peahens don’t even look at all those fancy feathers on the peacock (7/30/13). Now, another study on birds says that it’s smell, not looks, that attracts the females: “bird odor was a more reliable predictor of reproductive success than a male’s size or his plumage.” Do the males just grow all those ornaments for fun? Why would sexual or natural selection drive the extremes of ornamentation, if they really don’t make that big a difference to reproductive success?
Spider fandango: A cute and humorous case of male ornamentation and behavior was posted on Live Science about jumping spiders in Australia called peacock spiders. These little guys can dance! Only 4 mm in size, the males might have been overlooked but for photographer Jürgen Otto, who has patiently documented their mating rituals. The male sports a vividly colored tail flap that, “once unfurled, resembles an abstract Indian blanket of intense color,” which he shakes in a rapid courtship dance. Even those who hate spiders will have to admit that the antics of these critters are cute, especially when put to music, as shown in video clips included in the interview. Asked how this evolved, Otto said, “I am not sure, but it evolved probably in a similar fashion as it did in birds of paradise or peacocks, a result of sexual selection.”
There’s no question that extremes of sexual dimorphism occur in nature; but among other species within the same family or order, the males and females often look similar. This means that sexual selection, if it works at all, is not a universal principle in biology. Is it useful, then? Try that with any other explanation. “I’m a good student except when I’m not.” “I can answer any question except the ones I don’t know the answer to.” “I tell the truth except when I lie.” This is the kind of science bequeathed to us by Charles Darwin. Are we better off with his legacy? Send that charlatan back on the boat.