Ask anybody why they have sex, and their answers will range from "because it feels good," to "it helps my memory," to "in your dreams, perv." While all of these are technically valid points, a recent study by scientists at Stirling University appears to have uncovered the truth -- and it's not quite what you'd think.
Scientists have long theorized about the benefits of sexual vs asexual reproduction in the animal kingdom; since asexual (or clonal) reproduction uses far less energy and time, it should have replaced sex a long time ago by way of evolution. By looking at an organism that can reproduce both ways (the waterflea), the Scottish university's team realized that the genetic diversity of sexually produced offspring made them more resistant to parasitic infection than their clonal relatives.
In other words, sex helps our future generations fend off disease, so we have a genetic incentive to engage in it -- which is a lucky thing, because asexual cloning isn't nearly as much fun. Who ever heard of an asexual robot with heated genitals?