Evolutionary theory implies that the transition from one species to another takes many generations. There’s never going to be a point at which a non-human animal gives birth to a human offspring. But on the scale we use to measure things at Logarithmic History, the time 1.8 million years ago has a good claim to be the time when human beings began. (This should have been a June 8 post, but I was unavoidably off-line for a few days.) Genus Homo has been around for a while, but there are major evolutionary changes around now in the human direction. We can start with geography. It’s now that we find the first hominins outside of Africa, at least as far as Georgia in the Caucasus. The Dmanisi fossils from Georgia can probably be assigned to the new species Homo erectus, albeit somewhat shorter and smaller-brained than later erectus. Homo erectus also appears around this time in Africa. (The dates are so close that it’s even possible that erectus evolved outside Africa from an earlier emigrant we haven’t found yet, and then some of them migrated back to Africa.)
H. erectus has a bigger brain than earlier forms, and reduced jaws and teeth. And there are dramatic changes below the neck. Erectus has a body shape and size quite similar to ours. Strikingly, the changes in body form seem to be systematically related to distance running. Tendons in the feet and calves turn into springs that put a bounce in our running stride (but also rule out serious tree-climbing). Our neck gets longer and shoulders and head get more independent so we can swing arms for balance without twisting our heads from side to side. And the gluteus maximus becomes the largest muscle in the body, to prevent our bodies from toppling forward with each step. Homo erectus is the first hominin with a serious butt.
Moving from what we know to what we guess, it looks likely that Homo erectus had shifted to a new diet and a new mode of acquiring food. David Carrier argues that H. erectus was a persistence hunter, running after prey until they were exhausted. Human beings, although pretty poor sprinters, have a big advantage in distance running, in that our breathing is uncoupled from our running. This lets us run efficiently at whatever speed we choose. Most mammals, by contrast, have to breathe and run in synch, and pay a heavy price – wasting energy and overheating – for running at non-optimal speed. Bipedal dinosaurs enjoyed a similar advantage.
Like anything else in paleoanthropology, there are arguments about this. For example, fire may or may not have played a significant role at this early stage. We’ll cover some of these arguments in posts to come.