The Panda's Thumb

(Literary Masterpieces, Volume 15)

Stephen Jay Gould possesses the rare ability to write competently and interestingly about science for intelligent laymen. In this he is a national treasure and must be placed in the ranks of those possessing a similar ability such as Isaac Asimov, Lewis Thomas, and Carl Sagan. Gould’s latest collection of essays was originally published as columns in Natural History. The Panda’s Thumb follows on the heels of his equally readable Ever Since Darwin (1977), a collection drawn from the same journal.

The book is arranged in eight sections, but there is a single unifying theme running throughout: the principle of biological evolution. Gould is by profession a paleontologist but is obviously well read in other fields to which he relates the evolutionary idea. One finds, then, the following subthemes in his book: the major ideas of evolution, evidences for that principle, human evolution, science in cultural context, and debunking both of pseudoscience and of uncritically accepted scientific “orthodoxy.” In regard to the last, he is as gentle as possible in pointing out that Arthur Koestler’s notions about evolution are simply wrong; but he can also come down rather hard as he does in discussing the scientifically useless practice of measuring human skulls in attempting to establish differences of intelligence among races and between men and women.

Gould’s approach, although taking evolution as its central theme, is a blend of paleontology, anatomy, morphology, physiology, ecology, genetics, and borrowed ideas from other disciplines such as mathematics and physical science. He makes use of mathematics and physics, for example, in discussing “scaling theory” which deals with size and form as they change over time. The geometry of the organism has everything to do with the relation between, say, brain weight and body weight. There is a ratio that applies from the smallest to the largest animals. The percentage of the body weight taken up by the brain remains essentially the same. Interestingly, humans are the exception—the human brain takes up a greater percentage of body weight than in any other animal, and this is one, although not the only, reason why humans are preeminent among living things. It was not, by the way, the attainment of a large brain in proportion to body weight which marked the start of human evolution (the earlier orthodoxy) but rather the emergence of an upright stance. There is empirical evidence for this with the fossil “Lucy”—a small protohominid with upright posture and a small brain recently discovered in Africa.

Gould unabashedly advocates his own interpretation of the nature of evolution. The prevailing orthodoxy dating from the time of Darwin maintains that evolution is a slow gradual process involving the slow accumulation of “variations” (now termed “micromutations”) and then the eventual selection of those species able to obtain the environmental factors necessary for survival to reproductive age and the elimination of those less capable. This evolutionary interpretation fits neatly with the orthodoxy prevailing in geology—uniformitarianism—the theory that geological changes of the past were just like those of today, such as the gradual wearing down of a mountain by erosion over geological time. This uniformitarian perspective has been challenged now in both geology and the biological sciences. That it has been challenged does not mean that it is totally false and certainly does not mean, as some “scientific” creationists seem to think, that the old catastrophist view of the world is vindicated. It means, simply, that geological or biological catastrophic events could have occurred and, further, that they could have been significant in determining future states. Witness the recent hypothesis of Louis Alvarez which attributes the massive extinctions of organisms sixty-five to seventy million years ago to a catastrophic encounter between the earth and an asteroid perhaps five or six miles in extent.

Gould holds for an evolutionary theory of “punctuated equilibria” in opposition to “gradualism.” Evolution does not require gradual change as Darwin had supposed. The absence of transitional forms in the fossil record which would bear out gradualism is described by Gould as the “trade secret of paleontology.” Such transitional forms (missing links) are rare, Gould believes, because evolutionary change was so rapid that the chance of such forms being preserved as fossils is statistically very low. As he reads the fossil record (and this is the paleontologist’s job), Gould finds that most species exhibit no change over their lifetimes in geological time and that new species appear very quickly from the standpoint, once again, of geological time. So evolution takes place not simply in the gradual change of one species...

(The entire section is 1983 words.)