Darwin had reasoned that when one sex has to compete for mates, there’s greater pressure on it to evolve the features the other sex is looking for. It needs to be strong enough to beat off the competition, too. He called this evolutionary process ‘sexual selection’. And his observations suggested that males faced far more of this pressure than females. This would explain why the males of certain species, including our own, tend to be bigger and stronger than the females. It explains, too, such marvels of nature as the lion’s mane and the peacock’s flamboyant blue and green plumage.
