The Accidental Creationist
Why Stephen Jay Gould is bad for evolution.
Maybe Johnson's mistake was to use Gould as a source. Gould has repeatedly stressed the randomness of great species extinctions, and emphasized selection among species, while underplaying day-to-day selection within species. Indeed, Johnson's book cited Gould on all three of those themes. ("As usual," he wrote, "Gould is the most interesting commentator.")
RANDOM extinctions are a central theme of Gould's book "Wonderful Life." In using them to assault the notion of evolutionary progress, he took a different tack from Johnson's, but in the end he was no more successful.
The book is about the fossils of the Burgess Shale, products of an apparently sudden (as these things go) expansion of biological diversity around five hundred and seventy million years ago, at the beginning of the Cambrian Period. The subsequent history of the Shale animals, Gould argued, illustrates how radically bad luck can alter evolution's course. In particular, some very weird-looking Shale creatures had fallen prey to an essentially random mass extinction, and left no descendants. If not for this bad break, today's tree of life would presumably look very different.
Since Gould's book was published, his interpretation of these fossils has been challenged by a number of paleontologists. It now seems that the Burgess Shale animals weren't nearly so weird as Gould and some other researchers first thought; many fit readily into a standard taxonomic tree, and their descendants are with us still. In the case of a fossil so bizarre-looking that it was named Hallucigenia, Gould--following the then-prevailing interpretation-seems to have been looking at it upside down. Those baffling squiggly things on its "back" were legs. And those strangely spiky "legs" were spikes--armor, presumably the product of an arms race.
Still, Gould's premise is valid. Whether or not the Burgess Shale animals are a case in point, species do go extinct because of cosmic rolls of the dice. A meteor shows up and-poof!--no dinosaurs. But Gould's argument from this premise blurs the line between two separate issues: the question of whether a given species was likely to evolve and the question of whether the properties it embodies were likely to evolve.
For example, if our ancestors had been wiped out through bad luck, then, as Gould has repeatedly proclaimed, human beings would never have evolved. This point-in some ways the central point of "Wonderful Life"-is so unarguable that, as far as I know, it has never been argued against. No sober biologist would claim that there was some kind of inexorability to the evolution of Homo sapiens per se: a species five or six feet tall with ear lobes, bad jokes, and all the rest. The question is whether the evolution of some form of highly intelligent life was likely all along. In his first book on directionality, Gould simply skirted the question; in the second, he declared the answer to be no. The problem with this answer goes beyond Gould's overlooking arms races. The broader issue is what you might call natural selection's genius.
Though natural selection is a blind process that works by trial and error- and random trial, at that-it has a remarkable knack for invention, for finding and filling empty niches. It doesn't just invent great technologies; it keeps reinventing them. Flight and eyesight are two properties so amazing that creationists cite them for their implausibility. Yet flight has arisen through evolution on at least three separate occasions, and eyes have developed independently dozens of times.
Eyes are so favored by natural selection because light is a terrific medium of perception. It moves in straight lines, bounces off solid things, and travels faster than anything in the known universe. But smell, sound, touch, and taste are also amply represented in the animal kingdom, and are just the beginning of a long list of organic data-gathering technologies.
Indeed, humankind's vaunted twentieth-century advances in sensory technology seem almost like a long exercise in reinventing the wheel. We now have infrared sensors for night vision; rattlesnakes beat us to that one. We use sonar-old hat to bats and dolphins. Some burglar alarms work by creating electric fields and sensing disturbances in them; so do some fish, such as the elephant-snout fish of Africa.
Why is natural selection so attentive to sensory technologies? Because they facilitate adaptively flexible behavior. And what else does that? The ability to process all this sensory data and adjust behavior accordingly. In other words: brains-that is, intelligence as an abstract property. It is natural selection's demonstrable affinity for certain properties-its tendency to invent them and nurture them independently in myriad species-which renders trivial Gould's truism about how bad luck can wipe out any one species or group of species. The fates of particular species may depend on the luck of the draw. But the properties they embody were in the cards-at least, in the sense that the deck was stacked heavily in their favor.
Consider some properties of human intelligence which are often taken as defining assets of our species, such as language and the inventive use of tools. Though no species is nearly as accomplished as ours in either realm, primitive versions of these features are widespread.
The most obvious examples of tool use come from our close relatives, chimpanzees. Chimps pound nuts open with sticks and stones. They take twigs, strip them of leaves, poke them into termite nests, then pull them out and eat the termites. Some chimps even use sticks to brush each other's teeth. This sort of thing doesn't seem to be narrowly programmed by the genes. There is innovation and then emulation. In other words, there is cultural evolution-the selective transmission of nongenetic information from animal to animal.
Animals also can be surprisingly articulate. East African vervet monkeys have several warning calls, depending on the predator: one means "snake," one means "eagle," and one means "leopard," and each elicits an apt response (looking down, looking up, or running into the bush). Mastery of this language takes cultural fine-tuning. Young vervets may look up, see a pigeon, and give the "eagle" call. Adults then look up and, by failing to join in the call, induce an enlightening chagrin.