What Makes a Young Stud of a Booby? Bright Blue Feet & Impeccable Sperm

: It turns out that humans aren't too different from blue-footed boobies, at least when it comes to age and fertility. Researchers have recently discovered that the sperm of blue-footed boobies declines with age. And unlike humans, the blue feet of the boobies also fade with age, revealing that one reason why female boobies tend to mate with brighter-footed males is to ensure the robustness of the sperm and the health of their offspring. "The study provides us with a new way of looking at what lies behind sexual signals," lead author Alberto Velando told TIME, "pointing to the importance of sexual selection in eliminating genetic mutations." How the Heck: