It is noteworthy that it took roughly five million years before hominids—probably in the form of Homo erectus—finally developed the brains, the tools, and the legs to get out of Africa alive. There were big cats, hyenas, and wolves all along the way, and this may be one reason most of our hominid relatives never made it. It is striking, too, that, unlike so many other species—cats, for example—we are the only branch of our family (Hominidae) who survived the journey. In
