Feature Article - August 1998
by Do-While Jones

Do Brains Run Away?

Christopher Wills has an explanation for why people are smarter than apes. According to him,

As our cultures evolved in complexity, so did our brains, which then drove our bodies toward greater responsiveness and our cultures toward still greater complexity in a feedback loop. Big and clever brains led to more complex cultures and bodies better suited to take advantage of them, which in turn led to yet bigger and cleverer brains. … The uniqueness of our own evolutionary story lies in the fact that we, alone among the millions of species on the planet, seem to have been caught up in a process of runaway brain evolution.1 [italics in the original]

His theory is based on two experiments on rats. The first used food hidden in a maze to measure the intelligence of rats.

Back in 1922, … [Robert] Tryon used more sophisticated genetic techniques and an elaborate automated maze. Within three rat generations he had managed to produce strains that were distinctly different both from each other and the rats with which he had started. He named these selected strains maze-bright and maze-dull. During five subsequent generations of selection, the strains continued to diverge in their abilities. Tryon continued his selection for another twelve generations but obtained no further response.

The descendants of Tryon's maze-bright and maze-dull rats were maintained over the succeeding decades in the Berkeley rat colony, where they were often used as demonstration material in psychology labs or sent to other investigators around the world. In all the years that followed, the maze-bright and maze-dull lines retained their differences.2

In 1922, this was astonishing. Heredity was still poorly understood back then. Today, any good high school biology student could give the following explanation of the results.

During mating, each parent contributes half of the genes that the child will receive. Suppose there are some genes which give a rat the ability to find food quickly in a maze. Some children will receive fewer of the "bright" genes than others. If you keep breeding the dullest children, then after several generations, all the bright genes will be gone from the gene pool. Eventually the succeeding generations can't get any duller because there aren't any more bright genes to lose.

Similarly, there may be "dull" genes that prevent a rat from finding food quickly in a maze. If you selectively breed rats that don't have the dull genes, then the rats will eventually lose all the dull genes and will find food in the maze as fast as a rat possibly can. There will be no improvement in succeeding generations.

The key point is that two strains of rats were produced by removing undesired genes. New genes did not magically appear to make the rats brighter or duller. If new genes could magically appear out of nowhere, then the improvement would not have stopped after a few generations. New genes would have continued to appear, and the rats would have continued to diverge. In the experiment, the divergence stopped when all the undesired genes had been removed from the gene pool.

So, there is experimental proof that rats can inherit the genetic ability (or lack of ability) to find food in a maze. The question is, "Can cultural stimulation produce an increase in intelligence that is inherited?" To answer this question, Wills relates the results of a second experiment.

In 1963, when I was a graduate student in genetics at Berkeley, … psychologists David Krech and Michael Rosenzweig were performing experiments on a genetically uniform strain of rats.

The rats had been divided into two groups shortly after weaning. The first group was kept in bare cages in a soundproofed, darkened room, illuminated only occasionally by a dim red light (rats can hardly perceive light at that wavelength). …

The second group of rats was in a brightly lit animal room, full of bustle as workers came and went. They were kept in cages crowded with playthings-balls, exercise wheels, and so on. These rats were far more active than the ones in the darkened room. They surged around inside their cages and interacted continually. …

The contrast between the life-styles of these two groups could not have been more stark. Krech and Rosenzweig had designed their experiments to determine what influence, if any, the environment might have on the development of the rats' brains.3

After a while, they killed the rats and examined their brains. They found the rats from the "enriched environment" had increased acetylcholine levels, a thicker cerebral cortex, and more neuron connections. In other words, their brains were more developed than the sensory-deprived rats. So, mental exercise develops the brain, just like physical exercise develops muscles. Lack of mental exercise makes the brain atrophy, just like lack of physical exercise makes muscles atrophy.

We know, however, that a boy does not inherit muscles developed by his father in a gym. He has to go to the gym and exercise if he wants to be a champion body builder. Are brains somehow different? Can children really inherit wisdom or knowledge? Don't children have to read the books for themselves?

Christopher Wills did not report that after several generations the second experiment produced "strains that were distinctly different both from each other and the rats with which he had started." He didn't say anything at all about the descendants of either group of rats.

If the enriched-environment rats gave birth to rats that were maze-bright and the deprived rats gave birth to rats that were maze-dull, it would have proved that acquired characteristics can be inherited. They possibly would have won a Nobel Prize for that amazing discovery.

Either the biologists were "experiment dull" and didn't think to do this crucial part of the experiment; or they did the experiment and didn't report the results because the results failed to support their hypothesis. They have had 35 years to use environmental stimulation to breed a strain of maze-bright rats, but they haven't done it.

Our 20th century understanding of genetics is that neither physical nor mental exercise creates new genes. Complex culture does not produce any changes in the brain that can be inherited. The burden of proof is on Wills to show that modern science is wrong. He has had 35 years to show that the descendants of rats from an enriched environment are maze-bright, and hasn't done it. Therefore, it is reasonable to assume that his theory is wrong. Complex culture does not produce complex brains, which leads to more complex culture, which leads to more complex brains, and so on.

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Footnotes:

1Christopher Wills, The Runaway Brain, 1993, page xxii (Ev)
2 ibid. page 2
3 ibid. pages 1-2