17 of 21 people found the following review helpful
Interesting, informative, and enjoyable
, October 4, 2004
This review is from: The Throwing Madonna: Essays on the Brain (Paperback)
William Calvin is one of my favorite writers and thinkers on the brain. I don't always agree with his ideas, but he's creative in a way I enjoy and his ideas are always provocative and even pathbreaking in the way he integrates diverse areas--from linguistics to climatology--with the evolution and development of the brain.
This books brings together some of his best essays, covering a diverse array of topics. For those of you who aren't familiar with Calvin, this is an excellent introduction to his thought, which I can highly recommend.
Since we're on the subject, I thought I'd make a few comments on one of Calvin's interesting ideas--which is the proposition that spear-throwing was specifically the motor action that provided the stimulus for the subsequent evolution of the cerebral cortex and greater encephalization of the human brain. While I like this idea, and also am excited by the possbility of pinpointing such an important causative agent in our evolution, I also feel it's very difficult to isolate or pinpoint a specific action that could be responsible, but I'd like to consider it nevertheless in the light of what we do know about the development and nature of motor control in the human brain.
If you look at the pyramidal cortex, which has the most complex motor capabilities, we see that it's mainly specialized for fine hand movements and coordination. For example, typing or playing the piano or a musical instrument gets mediated by this area--or the fine control required by a surgeon's hand.
Rhythmic movements, even very fast ones, oddly enough, are not necessarily a highly evolved capability and in fact, if I remember right, are mediated by the cerebellar vermis, a structure in the cerebellum, or at least some portion of the cerebellum. We know from brain damage studies that people lose this ability from damage to the cerebellum. It has the tongue-twisting name of dysdiadocochinesia.
But getting back to the spear throwing capability, much of the eye-hand coordination for this sort of thing is in fact still mediated by the cerebellum. For example, it is known that scale transformation of muscle movements and velocity prediction occurs in the cerebellum in hard-wired circuits that are basically using tensor matrix multiplication to handle the scaling issues and mapping issues between sensory and motor control functions.
Speaking of "hard-wired" capabilities, I recall from my own studies of synaptic connectivity that the pyramidal cortex neurons have an average of about 3000 synapses with other neurons. Contrast this with those of the cerebellum, which are thought to have 100,000 connections, a truly staggering number. But this makes sense when you consider that it controls so many functions that have to be very quick and essentially automatic with very low time latencies and time constants.
And if you've ever seen the mathematical studies in the area of occulomotor control theory, which mostly looks at the optic tectum and superior colliculus areas, you know how complex that can get even though it's technically not a cortical area. Mathematically, it is using Voltera-kernel based integro-differential equations for predictive target tracking and so on.
So if you consider how advanced even the more primitive motor areas of the brain are, you have to find something pretty complex to require the intervention of the cerebral cortex.
And we haven't even talked about the last major motor area, the basal ganglia yet, which are just below the cortex, the putamen, caudate nucleus, and the globus pallidus. These structures are mainly responsible for the dynamic regulation of muscle tension through various neural pathways and feedback systems, mainly the gamma motor efferent system to the golgi tendon organs in the muscle fibers and the alpha motor pathways going to the intrafusal fibers of the annulospiral endings of the neuromuscular spindles.
Well, I didn't mean to wax so nerdy but anyway, that's about all the motor physiology I remember. :-) That wasn't my strongest area, exactly, being basically a sensory neurophysiologist and limbic system guy.
But anyway, to sum up, from what I recall, much of the coordination in throwing a spear would still be mediated by many of these more primitive areas below the cortex. It was the fine hand and finger manipulation movements and requirements that seem to me to have been responsible for the evolution of the more advanced pyramidal motor cortex.
However, all that having been said, Calvin could be right if the spear-throwing thing first got the evolution of the cortex going, and the pyramidal area then evolved later--which is basically what he's saying. My only problem with that is whether that ability requires the sort of control required by increasing encephalization. My understanding is that chimps don't have a pyramidal area, or at least a very highly developed one, and they can throw things just fine, but they couldn't play the piano, so that's another thing that sets us apart in addition to the language areas like Broca's and Wernicke's areas and so on, which they don't have to the same extent either.
I had one other topic I thought I'd comment on, which is a little off topic, but it pertains to the present sorry state of humanity and to the relationship between our current lifestyle and what we are basically evolved for, which, especially in the case of advanced western countries, with our sedentary jobs and lifestyle, is very different our evolution.
If you consider that chimps survive quite well with a brain of about 400-500 cubic centimeters, and the human average is almost four times that, all that extra brain power has just enabled us to get into more trouble. It seems clear to me that homo sapiens has evolved a brain much bigger than he needs and that accounts for his current sorry and unhappy state. :-)
To elaborate a bit, consider the difference between a typical Homo sapiens and a typical Neanderthal. Homo sapiens is a more "gracile" species, with longer, slighter, straighter bones, lighter musculature, but faster, more agile, and more active. The difference is much like that between a runner and a wrestler. Of course, there are groups that are somewhat more naturally heavier boned and heavily muscled, such as certain northern European groups, but they're the exception to the rule.
Basically, we're supposed to be chasing woolly rhinos and mammoths through the brush with fire-hardened and flint tipped spears rather than sitting at a computer screen all day totally sedentary, eating Pringles and drinking Cokes and not geting any exercise and getting fat. We're clearly evolved for a more active lifestyle and yet most of us, at least in the west, have jobs and lifestyles that are sendentary and relatively inactive.
All this leads to lifestyle-related diseases like high blood pressure, diabetes, atherosclerosis, and so on, notwithstanding the fact that psychologically we're not suited to just being that sendentary either and I think that contributes to a lot of individual and social malaise and unhappiness, especially if you consider that, according to health statistics, 50% of Americans over the age of 40 are overweight.
Anyway, just a few thoughts on one of Calvin's interesting recent ideas.
Help other customers find the most helpful reviews
Was this review helpful to you?