Why does sex exist? You might think the obvious answer is “reproduction” but there are plenty of organisms on Earth that don’t require sex to reproduce. And the more that scientists examined sex, they more they realized that it’s an expensive and inefficient way to get your genes to the next generation. The true purpose of sex is actually one of the longest-standing mysteries in evolutionary biology. But scientists are closer than ever to finding the answer. Here’s what we know about the evolutionary enigma of sex.