Why Do We Cry?
"As far as scientists can tell, we humans seem to be the only species that shed tears for emotional reasons." Is there an evolutionary advantage to emotions inspiring weeping? "Tears are universal. We need them to keep our eyes lubricated, but why on earth should streams of salty drops spew forth from our eyes, blurring our vision and making our eyes puffy when we get emotional? One theory is that crying may have evolved as a kind of signal—a signal that was valuable because it could only be picked up by those closest to us who could actually see our tears. Tears let our intimates in—people within a couple of feet of us, who would be more likely to help."