It looks like your kindergarten gut reaction to kissing might have been correct after all: it really is sick. Or, more specifically, the practice is designed to spread sickness. British scientists say the human habit of kissing evolved for less-than-romantic reasons, but one that is nonetheless important to a healthy reproductive relationship: to spread germs.
Last January, an Australian engineer announced a bizarre new contraceptive for men: a radio-controlled implant that could block the flow of sperm with the click of a button. The device, which is still in the conceptual stages, is the latest in a growing number of experimental male birth-control methods—including sperm plugs, sperm dissolvers and heat-inducing gels—that don’t tinker with testosterone.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.