Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. Auguste Rodin’s The Thinker is one of the art world’s most recognizable images. The monumental depiction of a man hunched forward, right hand resting against his chin, is synonymous with humanity’s capacity for deep contemplation, abstract thinking, and self-reflection. But while Rodin crafted his work of art in hopes of highlighting our unique cognitive abilities, the sculpture inadvertently highlights another facet that sets us apart from all other species: Homo sapiens are the only primates to boast chins. Consider humanity’s family tree. Our closest relative, the chimpanzee, lacks a jutting jaw line. The same goes not only for every other living ape, but extinct ancestors like the Neanderthals and the Denisovans. It’s easy to assume that humans evolved bony chins because they offer some form of additional facial protection—but the theory underscores a common misunderstanding when it comes to natural selection. Although Homo sapiens are the planet’s current dominant species, not every part of our anatomy necessarily contributed to …