Great apes have not always been humans’ closest living relatives. Only 2000 generations ago we still shared this planet with several upright-walking, fire-controlling, tool-manufacturing cousins, including big Neanderthals (Homo neanderthalensis) and small “Hobbits” (Homo floresiensis). With its various bipeds, it was a world reminiscent of Tolkien’s Middle Earth. Our ancestors 40,000 years ago would have had much less reason than we have today to believe they were far removed from the rest of the Earth’s creatures. We were but one of a group of similar species.
A picture persists of our ancestors evolving in a straightforward, single, and direct trajectory, up a stairway to Homo sapiens. This was not the case. For millions of years, many species of humans, technically called “hominins,” wandered the planet and sometimes shared the same valleys. For example, between 1.6 and 1.8 million years ago, there were three genera of distinct hominins (Australopithecus, Homo, and Paranthropus) each comprising several species, ranging from the slender Homo habilis, makers of stone tools, to the stockier Paranthropus robustus, with their massive, powerful jaws. Though there are debates about how many species need to be distinguished (a 2013 fossil find from Georgia suggests that species could be quite diverse), it is clear that for much of the past our ancestors shared the planet...
