The Panda's Thumb

The Panda’s Thumb: More Reflections in Natural History is a 1980 work of popular science by Harvard University paleontologist Stephen Jay Gould. Its 31 essays began life as articles for Gould’s “This View of Life” column, a 27-year fixture in Natural History magazine. Most of the essays discuss curious problems and episodes from evolutionary theory and history, considering both scientific issues and the political and social issues arising from scientific inquiry.

The book’s title essay discusses the evolutionary paradox posed by the panda’s “thumb.” Uniquely among ursine species, the panda eats bamboo, first stripping the leaves by rolling each bamboo stalk between its thumb and fingers. At first glance, it shouldn’t be possible for a bear to have a thumb: bears’ thumbs sit parallel to their fingers. Closer investigation, however, reveals this mystery is not what it appears to be. Pandas do in fact have five parallel digits, just like other bears. The panda’s “thumb” is totally unrelated to our own thumbs: It is an extension of a bone in the wrist.

Gould suggests that this adaptation provides a strong argument against the “intelligent design” thesis. While a divine Designer would have given all thumb-bearing species whatever the optimal thumb is (probably our own), evolution simply adapts what is already there. The very inelegance of the panda’s thumb suggests that it arose by random trial-and-error.



Other essays are similarly devoted to undermining anti-scientific arguments. He tells the story of the Piltdown man hoax (a falsified fossil of the “missing link” between ape and man), suggesting that Catholic theologian Pierre Teilhard de Chardin may have been the culprit. Another essay discusses Randolph Kirkpatrick, a British scientist of the early 20th century who proposed that Earth’s geological layers are formed from a single layer of fossilized amoeboid creatures. He called this layer the “nummulosphere,” and the theory earned him a great deal of public ridicule, despite his reputation as a scientist.

The book’s central essays discuss the history of evolution and popular misuses of the theory. One essay poses the question, why did Alfred Russell Wallace—who formulated the theory of natural selection at the same time as Darwin—never follow Darwin to the conclusion that human consciousness is also a product of evolution? Gould’s answer is that Wallace’s version of the theory of natural selection was more simplistic than Darwin’s. Where Wallace thought that every feature of every creature must have been directly selected for, Darwin believed that many organisms have characteristics that arose simply by accident, or as the chance corollaries of selected traits (the view which is currently held by biologists).

In Russell’s theory, the evolution of the human mind is hard to explain. The higher functions of consciousness—mathematics and the arts, say—do not obviously lead to a higher chance of procreating, especially in the rugged conditions in which human beings originally evolved. Wallace concluded that the mind must have arisen through some other process. Darwin, on the other hand, recognized that a feature—the mind—which evolved to cope with the complexity of early human social interaction would certainly be too complex not to bring with it some unselected, and entirely unpredictable, features.



Other essays focus on the ways the theory of evolution has been applied and misapplied since its discovery. Gould argues strongly against the idea that evolutionary theory provides credence to misogynist views of “the female brain,” or to any idea about gender based on essential biological traits or on a supposed primitive history in which, for example, men hunted while women gathered. He also traces the miserable history of evolution’s misuse to justify generations of bogus racial “science,” including the eugenic theories of the Nazis.

Some of the essays on evolution strike lighter notes, observing curiosities about the theory and its place in society. One essay discusses the “evolution” of Mickey Mouse, whose traits have changed with his changing context, like any other animal.

“A Quahog is a Quahog” discusses the question of whether human languages’ names for animals do or do not map onto the scientific classifications developed by taxonomists. He argues that, overall, they correspond surprisingly well at the species level. British English has separate names for Great Tits, Blue Tits, and Coal Tits, all different species although similar in appearance and behavior. Even undeveloped societies where scientific knowledge has not been widely disseminated tend to have different names for each local species, as identified by biologists. However, at higher levels of classification, such as “order,” “family,” and “class,” there is very little correspondence between ordinary and scientific language.



From this correspondence, Gould draws a striking conclusion. The fact that both ordinary language and science recognize the reality of species-difference implies, for Gould, that the visible “gaps” between species are a reality, not a theoretical imposition. Gould argues that this suggests that evolution proceeds in jumps, rather than gradual change: otherwise how did the “gaps” arise?

The Panda’s Thumb won the 1981 National Book Award in the “Science” category. Forty years on, some of its scientific content is out of date, but it remains an instructive account of evolutionary science for the lay reader.