Gould promotes the entity theory of evolution
By Brian Rosenberg
Why are people here? This was one of the questions addressed by Stephen Jay Gould, professor of paleontology at Harvard University, at a Tuesday-afternoon lecture on human evolution.
The lecture, sponsored by the Technology and Culture Seminar at MIT, was originally scheduled to be in 9-150. However, 15 minutes before the lecture was about to begin, it was moved to 26-100, after the original room had reached capacity. Room 26-100 eventually filled as well.
Gould began by characterizing the origin of humanity as "the result of a series of highly contingent events that would not happen again if we could rewind the tape" of human evolution.
Gould spoke on two competing classes of theories about human evolution and human nature in his lecture, titled "The Natural History of Human Evolution: Implications for Human Nature." The first class, which he called tendency theories, are being replaced by entity theories, he said.
He explained that tendency theories view the development of human consciousness as the result of "a predictable tendency, that natural selection favors something like humans." Entity theories, on the other hand, regard species of animals as entities that emerge through evolution, usually as the result of "quirky contingencies of history."
Tendency theories, Gould said, were supported by an incorrect view of what he called "evolutionary topology." Evolution tends to be portrayed as ladders rather than bushes, he said. "All textbook illustrations of evolutionary sequences are ladders," he said. Gould used the example of the evolution of the horse, describing how the illustrations show the ancestor of the horse becoming larger, merging its toes, and increasing brain size to become the modern day horse.
What these illustrations miss, Gould said, is the majority of species which evolve and then become extinct. "We tend to linearize evolutionary bushes," he said, adding that "horses are a pitiful remnant of their entire order."
Gould contended that the evolution of a successful branch of animals, such as rodents, was never shown because people "don't know how to handle that." He went on to say that when only one end of an evolutionary branch is left, as in the case of horses, that people tend to see that branch as the "culmination of a tendency."
Gould noted that human beings are part of just such a branch. And then asked, "Why are people here?" His first answer was that about 800 million years ago, a "small species of fish developed fins that were adaptable into weight-bearing structures" such as arms and legs. This development, he said, brought animals onto land, allowing humans to evolve.
His second answer was that mammals were spared when "whatever climactic changes occurred to wipe out the dinosaurs" about 65 million years ago. Gould's point was that there is no predictability to evolution that points to an overall trend toward human beings. Homo sapiens, or any other species, he said, is an entity, "just the latest branch of the evolutionary tree."
Gould then discussed the recent idea that there was a single "branching point of human origin" much more recently than had been thought previously. This conclusion, Gould explained, is based on a study done on a racially diverse group of people. The study found that the differences in DNA composition among those studied indicated that our species originated around 200,000 years ago in Africa.
The implications of this, Gould said, are far-reaching. "Human beings are less different racially than we ever thought," he said. Gould also speculated that the "commonality in human myths may be some historical memory." He suggested that the theory would also help establish ties between linguistic and genetic history.