Book Review

Defending the Cavewoman and Other Tales of Evolutionary Neurology

N Engl J Med 2000; 342:1616-1617May 25, 2000

Article

Defending the Cavewoman and Other Tales of Evolutionary Neurology
By Harold Klawans. 256 pp. New York, W.W. Norton, 2000. $24.95. ISBN: 0-393-04831-4

Evolution is still a questionable concept in some quarters. It seems that it has little to do with the practice of medicine. Indeed, I know a number of successful practitioners and professors of medicine who do not “believe” in evolution. In this book, a self-declared “classically trained neurologist” uses clinical tales from his own long and distinguished practice to show how evolutionary theory and solid facts about evolution provide indispensable background for understanding clinical cases and formulating successful treatments.

Using an ascendant principle in medical education — the use of case-based, problem-orientated teaching — Klawans introduces a broad range of evolutionary subjects and concepts, from the most general principles of the Darwinian evolution to the details of molecular, non-Darwinian approaches. He moves freely and confidently from Broca's old principle of the localization of functions in particular areas of the cerebral cortex to the reverse transcription of the genetic code in diseases caused by infectious proteins (prions). All this is done in a highly readable form by an author of both academic textbooks and literary works.

The first part of this book explores the unusual juvenilization and plasticity of the human brain in children raised in language-free environments, in aphasic patients in whom other functions, such as the ability to conduct music, were preserved, and in patients with early loss of the use of cortical areas, in whom a transfer of function to another area occurred. The plasticity of the brains of young mammals allows various functions to be learned with flexibility, according to the situations encountered. Over the course of human evolution, the period of brain plasticity has lengthened: human babies are born with brains that are less mature than those of their ape counterparts, and the period before sexual maturity in humans is approximately double that in chimpanzees. This increased ability to learn gives humans an adaptive advantage that allows the use of complex technology and gives them the ability to comprehend and maintain elaborate social systems.

As the ability to learn increased, language became a crucial tool with which knowledge could be communicated and societies organized to act coherently. Hence, Klawans devotes much attention to patients with language disabilities. He points out that the use of written language — an innovation of the past few millennia — profoundly changed the way the human brain works. As an example, he uses the case of a functionally illiterate man who was misjudged as unintelligent, whereas he simply saw the world in a different framework, one based on his personal experience and not on written information.

In the second part of the book, Klawans deals with a set of diseases that to a large extent are a byproduct of the latest phase of human evolution. Humans have removed the majority of natural-selection pressures while profoundly altering the environment. The author cites Huntington's chorea, a hereditary disorder that usually appears in adults in their late 30s, to show how the accumulation of mutations that leads to earlier onset of the disease is no longer countered by natural selection. “Mad cow disease” gives the author an opportunity not only to explain the molecular mechanism of the action of prions but also to stress that human intervention into the food chain opens up new ways for emergent diseases to spread. British cattle farmers turned traditional herbivores into carnivores by feeding their cows “rendered” meat, the parts of slaughterhouse carcasses that cannot be used for other purposes. Prions lurk in this discarded meat. By altering the environment and controlling human physiology at the molecular level, we have uncoupled human evolution from the evolution of DNA.

A few factual errors in the book, such as moving Jean Baptiste Lamarck, an early exponent of the theory of evolution, from the late 18th century back to the 17th century, do not detract from the value of the book. The depth of Klawans's insight awes me; I, an anthropologist specializing in human evolution, would not be able to write with the same ease and confidence about clinical neurology.

Maciej Henneberg, Ph.D., D.Sc.
University of Adelaide Medical School, Adelaide, SA 505, Australia