I have been pretty busy of late, but I have an urge to say something if only to prove I’m still alive so I thought I’d summarize what I know about the brain’s evolution and language. The main thing we know for an absolute certainty is that the brain suddenly got a lot bigger, about 3.3 times larger than the ape brains of Australopithecus of 2.5 million years ago.
Brains are expensive body parts. They put heavy metabolic demands on the system and they do not forgive malnutrition, especially in childhood. So the expansion of the brain size was only possible if food was reliable throughout the year. There are some possible trade-offs. We can sacrifice other metabolic demands. Chimpanzees and gorillas are much stronger than humans, strong enough to be able to tear humans apart. So we might have sacrificed some serious muscle strength in order to support our brains, but that only works if the ancestors found some substitute for muscle power. Stone tools were part of the kit of the earliest Homo and perhaps there were other wooden and vegetable tools that did not survive. Fire is another solution. Cooked food provides many more calories than raw stuff, but when did cooked food come into style? A quarter million years ago? Half a million? A million? A million and a half? There are advocates for each of these answers. I lean toward old dates, but who can say? It seems fairly clear that the brain was already growing when fire came along, but cooked food probably made further growth possible.
Another source of reliable food is cooperation and moral duties. In many societies, especially poor ones, people with food have a duty to share it with people (especially kin) who don’t have it. How far back do those customs go? I’m willing to say that sharing food probably goes back 2 million years to the earliest Homo habilis. Presumably, their manner of sharing was simple and without moral complexity, but sharing is a way to get everybody through the rough patches. One of the peculiarities of humans of every society is the shared feast. Mealtime is a social time. People eat together and pass food between themselves. Thus, the sick, the weak, the young, and the unlucky do not starve with anything like the frequency that starvation plagues animal societies.
Shared food is my own candidate for the earliest source of sufficient calories to support a bigger brain. Tools are the other candidate. Fire seems to imply sharing already existed (the idea of everybody making their own fire to cook their own hard won bit of meat is too nutso to tolerate). When fire came along, people were already first-class cooperators.
Meanwhile language may have been tagging along for the ride. I am a proponent of very old language, 2 million years old, but that first language was very simple, perhaps no more complex or rich than the speech of today’s eighteen month old. Language grew more complicated as the brain grew big enough to support more elaborate speech. That brings us to Deacon’s theory of the co-evolution of brain and language. It seems clear that the brain evolves more slowly than language does, so there was probably no co-evolution that favored a particular set of syntactical rules (sorry, Noam) but a more general co-evolution is quite possible. Clearer enunciation, increased vocabulary size, the ability to understand complete sentences as a unitary image, the use of abstractions and metaphors… all these things are part of every language but were probably not part of the bah-bah speech of M. and Mme. Habilis.
This raises another question. What did we do with all our new smarts? We did not just scale up the chimpanzee brain. The overwhelming growth was in the neocortical region with the cerebellum following not that far behind. One brain part that was unable to keep up with the increase was the corpus callosum, the wiring that links the two halves of the brain. Ours cannot allow for as much synchronization between right and left portions of the brain. Thus, the mere fact of getting a much bigger brain meant that significant localization of functions, particularly with new functions, was likely. A function would evolve on one side of the brain and not the other.
That localization suggests a role for consciousness. If the left side of the brain organizes language syntactically and the right side organizes it rhythmically, perhaps it takes consciousness (or even talking out loud) to put it all together. Years ago, on this blog, I cited work on Nicaraguan sign language that found rhythm was essential to creating language. Perhaps here is a reason. It gets the two halves of the overstuffed brain working together.
That may be fanciful, but even if not, the main key to organizing language has been the rise of many circuits in the brain linking the many parts together electrically. You can wonder how valuable all this brain imagery really is, but it has definitely established that there is no region of the brain controlling language the way there is a visual region and an auditory one. Language construction connects all these different parts to create a whole. When we think in words, we think of ways to connect the previously unconnected. Listening to a great story gets the whole brain chugging along. (While listening to a great liar (as we do these days) puts different parts of the brain in conflict.) That connecting seems to account for much of what our brain has been up to for the past two million years. It has been running wires from a billion point As to another billion point Bs and we are still working out the consequences of the change.
In other animals, the neocortex is largely used to handle sensory input and perception. In humans, it might seem that we have not used our brains to improve our senses, but language lets us know what is going on in other heads. Talking as sharing sounds too much like a 12-step program’s concept to appeal to me but it seems to have much in its favor. There seems no question that the main ways people have gotten so much more powerful is that they learn from history and each other. Without our big brains we’d still be babbling, but without language our big brains would just be a few trillion more cells to feed.