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The sexiest boobies have the bluest feet. If you had blue feet, you'd be a sexy booby too — at least if you were male. Moving on ...

First of all, the boobies in question are birds (you imagined something else?). They're known to ornithologists as Sula nebouxii and to nearly everyone else in the world as blue-footed boobies because they do have blue feet and because, well, could there possibly be a better name? Blue-footed boobies were first studied closely by Charles Darwin during his extended stay on the Galapagos Islands, but the birds are found in Peru and along the Pacific coast of Mexico as well.

Researchers have long believed that almost no wild animals — boobies included — live to old age, simply because parasites, predators or the elements get them first. This is bad news for the animals, but it isn't great for the scientists either since it makes it hard to study the natural process of senescence. We do know that in people, aging has an impact on all bodily functions — including, of course, fertility. In females, the ability to procreate stops after menopause; males can conceive even into their dotage, but oxidative damage to the sperm of men above 50 can make their offspring more prone to genetic diseases. Now, a new paper published in the Journal of Evolutionary Biology shows that the same can be true of male boobies.

The research, conducted by a joint Spanish-Mexican research team, focused on boobies because the still relatively isolated nature of their populations keeps them safe from at least some of the dangers that claim other animals in their prime. As male boobies age, the researchers found, their sperm suffers the same kinds of degeneration that human sperm does. At the same time, they change in more visible ways — including a fading of the distinctive blueness of their feet. Female boobies — no fools — generally give these seniors a pass, opting instead to mate with the boys who retain their blue hue.

It's not news that color, plumage and a thousand other visual cues serve as mating attractants among animals. But it is a surprise that the decline of reproductive signaling so closely mirrors a humanlike decline in sperm quality.

"The study provides us with a new way of looking at what lies behind sexual signals," says lead author Alberto Velando of the University of Vigo in Spain, "pointing to the importance of sexual selection in eliminating genetic mutations." Human males, alas, can't do much more about their sperm quality than boobies can. But unlike the boobies, we can at least buff up our blue suede shoes.

• Jeffrey Kluger
• Whether you're a male human or a male booby, aging ain't easy. New research shows that as male blue-footed boobies age, the birds' sperm suffers the same kinds of degeneration that human sperm does