Exploring the matter of sexual reproduction, biologists at the University of East Anglia found sexual competition ices the cake of ordinary selection. Because it provides many unseen genetic perks, the researchers say, the process of sexual selection, rife with male rivalry, is a dominant mechanism for reproduction among many populations.

If you look at sex through a biologist’s eyes, it is a hugely wasteful process. After all, only half of all sexual beings (the females) are capable of producing offspring, while the other half (the males) devote themselves solely to bearing the seed. Outside of The Bachelor, biologists say, sexual selection works in such a way that males must compete to be chosen by females to gain paternity. Only some pass this often cruel test.

Isn’t there another, more efficient way to maintain positive genetic variation than sexual reproduction?

Biologists theorize sex is necessary because the process of selection is usually based on general fitness and so it weeds out what they refer to as a high mutation load. Reproductive success depends on not just one or two aspects of a male’s condition but all aspects of his condition. To out-compete rivals and attract partners, a male has to be good at most things. Sex selection, then, may take ordinary selection one step further by purging negative mutations while maintaining positive variations in a population... and so the benefits may be worth the high costs.

To substantiate this hypothesis, University of East Anglia biologists began their experiment with the humble Tribolium flour beetle, a notorious pest that causes great loss and damage with its attacks on stored grain.

Necessary Competition

For the study, the biologists cultivated two separate populations of these promiscuous yet sturdy beetles controlling one difference between the two: the intensity of sexual selection during each adult reproductive stage. One population underwent intense competition, with 90 males competing for reproduction with just 10 females. Meanwhile, within the second population, the biologists paired single females with single males in monogamous bonds where the males did not compete and the females did not choose.

Here, they conducted a final stress test to compare the genetic strength of the beetles. After seven years of reproduction under these alternate conditions — for the beetles, this represented about 50 generations — the researchers enforced sexual inbreeding, where a brother mated with his sister in each generation, among the beetles.

In the face of inbreeding, the population of beetles that had experienced intense sexual selection maintained higher fitness and greater resilience to extinction. Some survived even after 20 inbred generations. By contrast, the beetles that had not experienced intense sexual selection showed more rapid declines in health when inbred — these beetles became extinct by the 10th generation.

“Our findings reveal that sexual selection reduces [mutation] load, improving population viability in the face of genetic stress,” wrote the authors at the conclusion of their study. Ultimately, Mother Nature requires competition and choice to best maintain our collective strength.

Source: Lumley AJ, Michalczyk L, Kitson JJN, et al. Sexual selection 1" protects against extinction. Nature. 2015.