Anatomical Modernity: When did we become us?
And now, emerging from dust;
we for the first time see, something like us.
Anatomical Modernity: What does that mean?
There are many ways to draw the line to decide when the “first humans” were around. You can look for the first tool use, the first use of fire, the first written language and many others. All of them are useful points to understand and are good answers to the question.
The point at which most researchers use to define the first humans is a point called “anatomical modernity” – the point at which fossils of humans are indistinguishable from modern humans. That point is roughly 300,000 years ago. These humans are referred to as ‘early modern humans’. Neanderthals and some of the older humans 500,000 years ago were pretty close to us. You would probably think they were human if you saw them wandering down the street in a T-shirt today (we have a post about that here). However, truly completely modern humans only arrive about 300,000 years ago.
What makes a human, human?
The main changes in human anatomy from our early ancestors to modern humans were:
- walking upright;
- smaller jaws and faces;
- slimmer skeletons (weaker, but lighter and better at running); and
- larger heads (i.e. brains).
Walking upright was first. Early Australopithecines walked upright, at least some of the time, 3 million years ago. However, they still have very long, flexible and powerful arms, implying that they were still spending some time in trees, climbing and swinging from branches. A proper upright-walking human, who had lost its tree-climbing adaptions came along with Homo Erectus 2 million years ago. They were able to run and hunt very successfully, probably vastly better than most humans alive today.
The changes in human faces and jaws are more complicated. Firstly, a surprisingly large amount of change in face shapes comes from the environment of a person’s childhood. For example, early humans probably spent 40 to 50% of their time chewing, eating much tougher foods. This changes the shape of one’s face significantly. It strengthens your jaw and gives you a bigger jaw and teeth, just the same way lifting weights does. This is why early humans, compared to modern humans, much nicer teeth and didn’t need braces. Present humans tend to eat much softer and mushier stuff, hence have smaller jaws, which means the teeth have less room and need surgical adjustment.
However, over time, humans started eating less and less tough plant material and eating more and more meat. This meant that our jaws and faces got smaller, as less force was needed to eat the plant material. Subsequently, when humans started settling down and growing their own food, this all changed again. But from about 3 million years ago to 500,000 years ago, humans did more hunting, ate more mean and therefore lost a lot of our strong facial structure.
The final change from apes to humans’ structure was getting slimmer and longer skeletons. This was to let us run faster and be more efficient. Monkey skeleton and muscle is actually shockingly strong compared to a human: chimpanzees can almost always outwrestle humans, even ones double their weight. This makes sense, chimpanzees arms carry a lot of their weight. However, they are heavy and dense for their size and can’t run and move quickly across open plains in the way humans can.
Increase in Brainsize: The real essence of humanity
The most important change was almost certainly the increase in brain size.
From 2 million years ago to 300,000 years ago, human brain size basically doubled. This is an incredibly rapid change by evolutionary standards. Imagine something like height or weight doubling in this time. You would create a new animal.
This makes sense in some ways. Generally, having a bigger brain compared to your body makes you smarter. Some of the less intelligent animals tend to have tiny brains and massive bodies (looking at you stegosaurus, it’s a wonder you could even move) whereas humans, birds, octopuses have much larger brains. This makes sense at some level, smarter animals have smarter brains, so evolution was selecting for smarter humans, with the less smart ones dying out.
However, thinking about it in more detail, this is incredibly weird. How was human intelligence manifesting through this period? There were some basic stone tools, some basic use of fire, but no art or written language. It wasn’t as if cave lions were administering IQ tests to humans and only eating the dumb ones. It makes sense that, generally, smarter humans would do better, so they would pass on their genes. The problem is that this selection must have been incredibly strong to result in a doubling of brain capacity this quickly. And it’s hard to imagine how?
The answer is probably something to do with co-operation. It’s something we take for granted, but it’s actually really hard to co-ordinate with another person to achieve a complex task. Anyone who remembers doing group assignments knows this. Some mammals can co-operate a little bit on certain tasks, for instance, wolves hunting. But for more intelligent creatures like early humans, who could all choose to run away and abandon the tribe at any moment, or betray someone to take their food or their status in a tribe, to all co-ordinate clearly required a lot of planning and communicating.
So really, what was probably happening here is that human brains were evolving, through interacting with other human brains.
This is so fascinating, because it once again, demonstrates the idea that that organism and the environment are fundamentally linked. Just in the same way that the first oxygen-creating creatures came along and fundamentally changed the atmosphere, and then needed to adapt to that atmosphere, human beings changed by being exposed to other human beings. Human beings evolved to be better at working with other human beings, to work together better and use each other as a resource. Evolution doesn’t just act on solitary individuals, it acts on groups, cultures, civilizations.
Were early humans, human?
Despite this massive increase in brain size, there were still several things that early humans were not doing, in particular, written language, art and complex tools. We are going to talk about all these things a lot in the next posts (art and tools, written language).
However, these are some of the most fundamental aspects of being a human being. So despite being physically identical to us, if you grabbed an early human out of their environment and put them in ours, they wouldn’t do well. They wouldn’t be able to read or draw or really understand what was going on around them. And even if you tried to explain it to them, they would probably freak out and wouldn’t be able to learn it. There are even examples of things like this happening with actual modern humans, basically, orphaned children who had no contact with other people throughout their childhood, being taken in and raised in their adulthood – they didn’t generally go well. As amazing as the human brain is, it would probably have been all a bit too much.
This tells one very important thing: humans aren’t human on their own. Really, this is true for all animals, but in particular with human beings. Even once we had the neurological tools to learn and do all the things that modern humans do, it took us a very long time to do those things, that today we think are obvious. Humans and their ancestors have had basic hand axes for more than 3 million years. It was only about 50,000 years ago that we thought to attach a shaft and create a modern ax. To go from a car to a rocket is nothing once you’ve worked out the scientific method and what atoms are. It’s just a matter of following the path. But it took hundreds of lifetimes for humans to enter the Stone Age (that’s our next post) and start imagining and start creating.
That gives you a sense of just how hard it all is. And just how much we take for granted.
