The root of human progress

(or, “Where your iPod really came from”)

There’s this odd thought I get on a semi-regular basis; let’s say a few times per month. Here’s the gist: I’m walking down a busy street, such as Montreal’s Ste. Catherine Street, on a busy afternoon. I abruptly become aware that there are roughly a hundred thousand or so visible objects in my immediate surroundings; gold watches, sweater zippers, cell phones, noserings, Toyotas, handbags, bricks, iPods, and the like. That’s not the weird part, though. Immediately following this otherwise mundane bit of cognition is always the idea that all of these objects, and in fact every human-made object or bit of technology, would not exist but for a small lump of tissue at approximately the level of the passing bike courier’s bridge piercing [N.B. it’s a piercing that goes through the bridge of the nose just below and between the eyebrows; I had to look it up, too].

Scientists and philosophers have long wondered what it is that makes us uniquely human. Descartes believed that we were animated by a soul that interacted with the body through a structure known as the pineal gland. Having seen a few in person, I’m more inclined towards the current view that the pineal gland is more suited for producing melatonin than housing souls. To be sure, this is a difficult question to answer, but there are a few things we can be sure of.

Firstly, whatever it is that distinguishes humans from other animals must be reflected in our behaviour; obviously the human-animal distinction is more than aesthetic, or else we wouldn’t be the only creatures with the aforementioned zippers and iPods, to say nothing of the fact that you’re most likely reading this document over the internet on a computer. If we can assume that our humanity is represented in our behaviour, then what is the origin of our behaviour? We have a conclusive answer for this as well; behaviour, as with emotion and cognition, is a product of the brain. There are minor exceptions, if you consider reflexes in the peripheral nervous system to be behaviour, but we can safely say that volitional behaviour arises from neurobiological processes between your ears.

So particular behaviours distinguish us as human. Behaviours arise from the brain. How is the human brain unique?

Across the temporal branches of evolution (or ‘phylogenetically’), the brain has changed significantly. It’s too broad of a topic to go into detail in this context, but suffice it to say there have been some broad trends in the evolution of the brain. For one thing, certain parts of the brain are phylogenetically older. Your limbic system for example, which contains such critical structures as the hippocampus and amygdala, appears to have a somewhat earlier origin than other parts of your brain. The brain has gained new folds (gyri and sulci), most likely to increase the ratio of its surface area to its volume. Brains also became larger relative to overall body size.

What was the great leap forward in brain evolution with the appearance of our own species? Coming back to the bike messenger, a few inches away from that spike above his eyes lies a structure referred to as the prefrontal cortex, part of the neocortex. This is, phylogenetically, a relatively ‘new’ region, and one that appears in mammals and gains size (and ostensibly function) in primates such as ourselves. While our non-human primate cousins also have this brain structure, it represents a larger proportion of the human brain (see for example Semendeferi et al., 2001, American Journal of Physical Anthropology 114: 224-241). This may explain why, although primates display many human-like traits, we have little trouble distinguishing human behaviour from that of other primates.

Which gets to the heart of what messes with my head so much on Ste. Catherine. We have brains that are remarkably similar to those of chimpanzees. Leave chimpanzees on a human-free world for tens of millions of years, though, and in the absence of further brain changes you’ll have tens of millions of years without skyscrapers, sea-doos, sonnets, and Scud missiles. For better or worse, adding a bit of tissue to the neocortex seems to change all that, making possible every human-made object you’ll ever encounter. Whether you find that information disturbing or fascinating, I empathize.

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Posted in Neuroscience, Public Education.

Posted on 02 Sep 2011

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