But if we're going to talk about the human evolutionary trajectory, we know that our species is about 200,000 years old. Our genus is around 2.4 million years old. So the question becomes when do we start seeing any of these symptoms, if you will. It's very interesting that there's a cave in South Africa, Rising Star cave, that is the home of this human, perhaps ancestor, but hominid in any case, called Homo naledi and apparently there were numbers of individuals who were literally dragged by others into a very deep, subterranean chamber in this cave.