Evolution and the Brain

The brain is an organ with over 500 million years of evolution. It probably evolved through integration centers in nerve nets, the early brainless nervous system. 

From the reptilian brain to the mammal brain and then the primate brain, brain development (evolutionary sense) is about adding on further capabilities, not replacing or rebuilding. So the human brain still uses mammalian and reptilian brain structures. It is an organ of such complexity that understanding it in detail will keep us busy for quite a while.

That said, we are living in an era where a lot of progress is being made. One of the central questions to answer is how this organ evolved into a tool for abstract thinking. And slowly we are lifting the curtain on this. I offer just a few thoughts in what follows.

Photo by Robina Weermeijer on Unsplash

Nematodes appeared more than 500 million years ago. They have a nervous system of a few hundred neurons but no brain as such. The nervous system of the C elegans has been completed mapped and is heavily studied. It contains 302 neurons in total of which about 200 are organised into a nerve ring. In comparison, the human brain as around 100 billion neurons. Interestingly enough it has already some interesting capabilities:

Let me quote from a recent science news article of the University of Leeds  What worms can tell us about brains and behaviour. It reports on research on the nerve ring ('its brain') of C. elegans.

Professor Cohen’s recent work, published in Nature in 2021, maps the structure of this brain, and builds a complete brain-map of its circuitry. The current study adds another important level of understanding: the link to behaviour. Even though the brain is very compact, the animal displays a range of complex behaviours, and neuroscientists have been interested in understanding its brain for decades.

The new research revealed three novel observations:
• neurons track behaviour not only of the present moment but also the recent past
• they tune their encoding of behaviours, such as motion, based on a surprising variety of factors
• and many neurons simultaneously encode multiple behaviours.

Another major outcome of the team’s work was that while most neurons always obeyed the predictions of the model, a smaller set of neurons in the worm’s brain—about 30 percent of those that encode behaviour—was able to flexibly remap their behaviour encoding, essentially taking on new jobs.

Suprisingly this primordial brain already exhibits many of the main base functions: sensory experience, (reasonably complex) encoding of behaviour, memory and (maybe surprisingly) task flexibility. If this can be done with a few hundred neurons, what about 100 billion?

The brain works heavily with associations, out of which concepts are naturally born. This process turns atomic entities (a sensory signal) into a composite of associations. For the brain to be able to work with these assocations it must do some sort of labeling so they can be referenced. That starts to sound very much like the appearance of language.

Some sort of (internal) language must have developed - signs, meanings, and a code connecting signs with their meanings. Retention, i.e. memory, is of paramount importance. The brain has a very pragmatic approach to this: what remains active remains retained in memory. Replaying recent experiences is one of the maintenance tasks of the brain. And when it replays these experiences it replays its associations at the same time.

Once a language exists one can expect it to evolve as the brain evolves. In an article "Evolution of Brain and Language" - an interesting read - the author states the following:

The evolution of brain circuits, therefore, cannot be understood independent of the evolution of language, and vice versa, which means the coevolution of brain and language—and, in fact, language itself—can be understood as a complex adaptive system.

It makes sense to look at the evolution of language in the same way as we look at the evolution of species or organs.

And with language comes culture. Culture uses language as its non-physical inheritance mechanism of values and beliefs, norms, symbols, language, artifacts and rituals. These social interactions create and maintain information stores retained within a specific group of a species. Each one of these groups drives their own mental evolution. The more intense the social interactions, the greater the capacity of potential mental evolution.

For a long time, this mental evolution of the brain was slow with respect to the life expectancy of the species or the physical evolution of the brain. However, over the last ten thousand years human social activity within specific cultures has intensified to such an extent that the cultural context in which individuals live their later life is completely different from the cultural context they were brought up in. There is an exponential increase in the amount of information that is part of cultural transmission. It looks more and more that the mental evolution has decoupled from the physical evolution. 

This decoupling from the physical pushes us towards virtual worlds as we look to intensify these interactions further. It is a road of discovery, no guarantee that we will find paradise. But I am ready for the journey.