Evolution has created a staggering range of organisms, each with features cleverly honed for its environmental niche. But while evolution is a fantastic creator, adding almost whatever is needed, it is surprisingly lazy at tidying up after itself, at pruning what is no longer required. In the bacterial world, where margins for survival may be razor sharp, things are more efficient. But most animals carry with them a surplus of obsolete features, such as the astronomical quantities of pathological DNA interlopers that sit in every cell in our bodies. But there are also more large-scale examples of detritus we endure. For instance, whenever we get cold, our hair duly stands on end to create a buffer of trapped air around our skins, as if such an action would make any difference to keep us cocooned from the cold—it doesn’t (unlike other primates, we simply don’t have enough hair to make this automatic response functional).