CHAPTER 7



BRAINS


et's come at this problem a different way. We're told that the DNA of chimpanzees is over 98% the same as ours. If so, then there's more to it than DNA because chimps don't compose symphonies or do mathematics; (Note 1). We don't have fur, only vestigial hair, except on our heads, we walk upright (bipedal) but our infants do crawl on all fours. Apes can walk upright but generally go on all fours. Apes are generally vegetarians, although chimps occasionally hunt and eat monkeys. Humans are generally carnivorous (meat eaters). Ape brain case capacity is about a quarter to a third of ours and their heads and limbs are shaped differently from ours.

When we try to trace our lineage back we can't tell whether hominids had fur or skin like ours, what they ate, even how they walked, but we can tell brain case capacity from fossils. It's true that female humans are slightly smaller in build than males. They have correspondingly smaller brain cases, but no one would argue that they have less brain power than males. Since females have entered professional accounting and competed with males in final exams in Canada, although far fewer in numbers than male candidates they have begun to equal males in the honours lists and as medallists. So a 10% smaller brain case does not necessarily mean 10% less brain power. Mentally retarded adults still have normal-sized brain cases. The organization of the internal structure of the brain and our inherent mental ability is then at least as important as overall size. But, having noted these facts it is still statistically true to say that human brain cases are 3 to 4 times larger than that of the great apes living today. Bearing in mind these limitations, we are entitled to consider brain case size as a significant factor in determining whether a fossil skull, by its shape and size, is likely to have been a human or near-human (if there is such a creature) or if you prefer the Latin for humans, homo sapiens sapiens. How far back then, can we trace fossil brain cases similar in capacity to our own?

During the last 100 years pieces of fossil skulls and various bones that look somewhat human have been dug up by archaeologists or excavated by accident in various parts of the world. Apparently almost none of them are directly similar to each other unless found in groups. Each discovery of potentially human-like fossil remains was usually named after the place of discovery. Eventually this got out of hand. Instead, the phrase, Homo Erectus, or upright man, was coined to cover these different discoveries. Not all archaeologists, particularly those in France, agreed with this. For one thing, it contained the presumption that these were 'man,' homo being the latin word for man. But are we all descended from these various scattered half-million or so years old "homo erectus" specimens with a brain capacity of about 1,000 ccs or less?

At Fontechevade in S.W. France, in a cave, among twenty vertical feet of debris, was found an incomplete skull cap----its cranial capacity has been estimated as about 1465 ccs. Small pieces of a second skull indicated brow ridges as small as in European women today, quite unlike the heavy Neanderthal and ape brow ridges. Age is estimated between 85,000 and 135,000 years.

The Swanscombe specimen found in a gravel pit in Kent, in England, is said to be about 250,000 years old. It has an estimated cranial capacity of 1325 - 1350 ccs., virtually the same as for a modern human. The slope at the rear of the skull was smoothly rounded as in human beings today, not squat and bun-shaped like Homo Erectus and Neanderthal. Fossil bone found near the skull (but not positively identified with it) has been radio-carbon dated to more than 272,000 years before present (BP).

The Steinheim skull was found in a gravel pit near Stuttgart, Germany. It has an estimated cranial capacity of about 1150 ccs -- at the low end of our present cranial capacity. The dating may be similar to that of the Swanscombe specimen.

At Vertesszollos in Hungary in the mid-1960s was found a single occipital (back of the head) bone and stone "tools" associated with it. From this bone the cranial capacity has been estimated to be between 1405 and 1600 ccs. (Our present day average is about 1350 ccs.) This fossil is said to be between 400,000 and 700,000 years old.

I suggest we discount the accuracy of the Hungary specimen. When there is no skull cap to work with, the calculation of cranial capacity must be based on certain assumptions which may or may not be correct. Even without the Hungarian fossil we have a time sequence from say, about 100,000 years ago through 250,000 years ago with estimated cranial capacities entirely within our present human range.

What this presumably does is rule out the idea of the low-brain-size descendants of the batch of various primates grouped together as Homo Erectus having preceded modern man as potential ancestors. They are ruled out because the fossil record we have listed above precedes some of these other so-called ancestors. A more appropriate view might be that there is a sequence of high brain capacity individuals continuing at least several hundred thousand years into the past.

Instead of our own evolution from 'homo erectus' we seem to have certain ancient primates with a brain capacity up to about twice that of living apes, but who in half a million years did no more than use simple flint tools, hunt, and use fire. Apart from the use of fire, this places them not much above the level of existing chimpanzees who hunt in groups with considerable skill and use a variety of specially selected tools.

What we seem to find is a series of apes of different sorts and sizes between 5 million and 1.5 million years ago. As we have living great apes today, it appears logical to conclude that the long-ago apes were the precursors of our living apes. Then there is apparently a gap of over a million years after which from about 500,000 years ago down to about 35,000 years ago appear a few humanoid fossils with brain cases resembling present human size. But all they accomplished seems to have been creation of simple stone tools and possible use of fire.

This information may be helpful in understanding the ancestry of our living great apes, as part of the animal world, but none of it, I suggest, tells us how we came to be what we are. As human beings, we are quite different in abilities and achievements.


NOTE 1

On December 7, 2002 the National Post daily newspaper in Toronto page A2 carried a headline:

Humans share 99% of genes with mice

This came from a report by a group of scientists published in the scientific journal Nature. There, the Post stated, it was said that humans shared all but 300 of a total package of 30,000 genes with mice.

To this I would add that we are certainly very different from mice, so genes cannot be as important a differentiating factor as scientists apparently suggest. What we do have in common is that all three species, humans, mice and chimps, are mammals. All three have one heart, one blood supply, one nose, one mouth, one stomach, one liver, and one central nervous system; two ears, two eyes, two lungs, two legs and two arms or equivalent for mice. That is at about the level in which we are similar, so it would seem this is probably the level at which the genes are operating, and therefore has very little to do with anything beyond the cerebellum/hippocampus level of the brain. It seems to be the size and content of the advanced brain, the cerebrum, resting above the lower level which apparently makes us human at our present level.

It may be, then, that mammals all began with the same physical template and were endowed with or developed niche characteristics which make us and maintain us at levels of specialization that we now possess. Mice may not be able to build or fly a plane at supersonic speed, but few if any humans could master 300 turns of a maze in three days to find a piece of cheese in the middle.

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