THE RUNAWAY BRAIN

The Evolution of Human Uniqueness

Christopher Wills

London, 1993.


Wills' compendious history of our species ranges over paleoanthropology, the significance of mitochondria, and the doctrinal wrangles over evolutionary theory.

One of the most important mutational processes in evolution is gene duplication, whereby a copy of a gene is inscribed elsewhere in the genome. This increases, obviously, the number of genes that the organism has. If the duplication is precise, the duplicate genes do the same job, but imperfect copies are mutations which may enable different but related functions to be carried out.

Genes that regulate embryonic development share a short segment of DNA called a homeobox. Homeobox genes have undergone gene duplication in the course of evolution, although not as readily as other genes, since their function is presumably more fundamental.

Profound questions arise in the case of brain evolution. Although the forebrain is highly complex and differentiated in humans, it may not be the most recently evolved.

"The early vertebrate brain seems to have evolved, not through the addition of a forebrain onto the head end of the neural tube, but through a lengthening of the neural tube just behind the head end. This lengthening allowed additional swellings of the neural tube to take place, swellings that eventually gave rise to the midbrain and hindbrain. In the process various homeobox genes have taken up new functions. It was this stretching of the neural tube that first laid the groundwork for our own enormously complex three-part brains." (p.258)

It seems that gene duplication may have led to map duplication in the brain, an issue of great interest on this site (see Cognitive Mapping).

"Because the brain's circuitry is so highly parallel and the rate at which information is processed in each set of circuits is so slow, it seems that it has not been possible simply to add to the complexity of a single map in only one part of the brain and to make it more and more detailed in the process. Instead, the brain distributes information into many different, less detailed maps in different regions." (p.297)

Differentiation of function is then enabled by the development of visual, auditory and other maps, leading to the "runaway brain".

The other side of the story is culture. Wills argues that the "evolution of human uniqueness" is explicable in terms of genotype-culture feedback loops.

He notes that it is not possible to figure out which parts of our genetic capital are the most valuable, but that we may aspire to do something about the this other aspect:/

"Rather than trying to modify our genes, we would do well to concentrate on enriching the environment of every individual, for in the process we will be drawing more fully on our genetic capital." (p.284)

This can be compared with Fuller's recommendation that we reform the environment.



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