Controversy in Evolutionary Biology
According to the noted British geneticist John Maynard Smith, Harvard paleontologist Stephen Jay Gould is "a man whose ideas are so confused as to be hardly worth bothering with." Oxford University zoologist Richard Dawkins, author of the best-selling book The Selfish Gene, charges that Gould's view of evolution is based on a fundamental misunderstanding. Tufts University philosopher Daniel Dennett goes further. According to Dennett, Gould is "a would-be revolutionary" who has mounted a series of attacks on conventional Darwinism over the years. Furthermore, Dennett says, as the best-known writer on evolutionary topics, Gould has had an influence that is "immense and distorting." Gould must have some "hidden agenda," Dennett speculates. Perhaps it is Gould's Marxist leanings, he says, that have caused him to attack accepted evolutionary theory.
Gould, on the other hand, brands Maynard Smith, Dawkins, and Dennett as "Darwinian fundamentalists," who place an emphasis on one component of Charles Darwin's thinking and "push their line with an almost theological fervor." Maynard Smith, he says, has apparently gotten caught up in an "apocalyptic ultra-Darwinian fervor." Dennett's writings, he adds, are characterized by "hint, innuendo, false attribution and error." If the Victorian era British biologist T. E. Huxley had been "Darwin's bulldog," Gould concludes, then perhaps Dennett should be characterized as "Dawkins's lapdog."
Maynard Smith, Dawkins, Dennett, and Gould are not the only individuals engaged in this controversy.For example, Gould's colleague, paleontologist Niles Eldredge of the American Museum of Natural History, has also criticized Dawkins, Dennett, and Maynard Smith. So have various other scientists, such as geneticist H. Allen Orr of the University of Rochester in New York. Evolutionary psychologists such as Steven Pinker of the Massachusetts Institute of Technology and Leda Cosmides and John Tooby of the University of California at Santa Barbara are members of the other camp. The controversy is more than an argument between Gould and his critics. It is one in which numerous scientists are currently engaged because they believe that there are still questions to be settled about the nature of evolution.
Before I go any further, I should point out that none of the participants in this controversy is questioning the idea of evolution. They are all well-known evolutionary biologists with the exception of Dennett, a philosopher who is the author of Darwin's Dangerous Idea, which was a finalist for the 1995 National Book Award. They all agree that the evidence that evolution has taken place is overwhelming, and they all oppose creationism, which they consider to be an attack on science. Furthermore, they all agree that Darwin's idea that natural selection is the main mechanism of evolutionary change is correct. And, of course, they all tend to view themselves as Darwin's intellectual heirs. What are they arguing about, then?
Darwin's theory of evolution is universally accepted among biologists. However, Darwin's "theory" is not a single idea; some scientists have broken it down into five or more subtheories. Thus it is possible for scientists to agree on many of the details of the theory while arguing about others. Furthermore, it is possible to agree that natural selection is the main cause of evolution, while debating the details of how evolution has happened.
Controversies About the Role of Natural Selection
The idea of evolution was not original with Charles Darwin. On the contrary, it was an idea that had been widely discussed for decades when Darwin published his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life in 1859. Darwin's great achievement was to amass evidence sufficient to convince his scientific contemporaries that evolution had indeed taken place, and to suggest a mechanism, natural selection, that would cause species to evolve.
Darwin realized that the members of every species were capable of producing more offspring than could survive. As Darwin noted, this is true even of such slow-breeding species as the elephant. If all the offspring of a herd of elephants lived to maturity and produced offspring of their own, the world would be overrun with elephants in no more than a few thousand years. Darwin reasoned that some members of a species were more likely to survive and reproduce than others. Those that did would pass their characteristics along to succeeding generations. If there was originally a certain amount of variation in a species, some characteristics would be preserved, while others would be weeded out. Over long periods of time the species would change; gradual evolution would take place.
Natural selection does not require that the better-adapted members of a species always survive and reproduce. If they possess characteristics that make survival 1 percent or even a fraction of a percent more likely, then on the average they will have more offspring than other members of the species. Thus if some of the evolutionary ancestors of the giraffe were able to obtain more food than other giraffes because they had longer necks, then long-necked animals would eventually come to predominate and eventually evolve into the giraffe that exists today. If an antelope could run a little faster than others, it would be more likely to escape predators and reproduce. Its offspring most likely would also be a little faster. Eventually that characteristic would spread throughout the population and in time all antelopes would be swifter.
Natural selection is an idea that is beguiling in its simplicity. Once you understand it, it is easy to become convinced that evolution could happen no other way. However, since the time of Darwin, some scientists have thought that natural selection was not the only driving force behind evolution. In Darwin's day, some biologists thought that there were other important factors. Some of them believed, for example, that some inner force drove human evolution toward greater intelligence. This idea was somewhat metaphysical and today it is thought to be totally discredited. However, scientists have never stopped looking for factors other than natural selection that might influence evolutionary change.
Stephen Jay Gould and his colleague Niles Eldredge are perhaps the best-known scientists who proclaim such a belief. Consequently their names--especially that of Gould, who is the more vocal and contentious of the two--are frequently mentioned by those engaged in the controversies that such ideas have caused. Gould and Eldredge believe that natural selection acting on individual organisms is the main cause of evolutionary change. But they also think that there are phenomena that appear at higher levels of complexity. They claim that, just as some individuals are more likely to survive than others, species also have different probabilities of survival. Furthermore, Gould says, some evolutionary lines give rise to more new species than others. Surely, he suggests, this is a factor in evolution too.
Gould's and Eldredge's theory has been attacked by such orthodox Darwinists as Richard Dawkins and Maynard Smith, who continue to insist that only natural selection is important. In reply, Gould has contrasted Dawkins's and Maynard Smith's "Darwinian fundamentalism" with his and Eldredge's "evolutionary pluralism." The controversy is still going on, and it is not likely that the argument will end soon. The differences between the two groups of scientists do not arise from their interpretations of scientific data. There are fundamental philosophical differences between them. Dawkins, Maynard Smith, and other orthodox Darwinians are reductionists* who see only one important factor in evolution. Gould and Eldredge, on the other hand, describe themselves as pluralists who see evolution as something that is much more complex.
The differences in outlook have led to not one but a variety of different controversies. The first one erupted in 1979 when Gould and Harvard geneticist Richard Lewontin published a paper in which they criticized methods that, they claimed, were commonly used by evolutionary biologists. Rather than looking at organisms as integrated wholes, Gould and Lewontin said, these scientists reductively broke them down into collections of individual "traits" and then invented stories that purported to explain why these traits had evolved. But, the two authors said, there was often no evidence to support these sometimes fanciful stories. Gould and Lewontin then went on to maintain that organisms often had traits (which they called spandrels, after the architectural term) that had evolved for no adaptive purpose--in other words, traits that had appeared as by-products of other evolutionary changes.
Looking at the Evidence
The recent controversies in evolutionary biology are far from being settled. On the contrary, they are multiplying, and reasoned arguments have increasingly given way to vituperation. One of the reasons is that there has not been sufficient evidence to answer the questions that have been raised. However, evolutionary biology is anything but a stagnant field. New discoveries are made almost every day. Some of them are beginning to shed some light on the issues that are being argued about. At the same time new questions are being raised.
For example, recent field studies have shown that, in some cases, natural selection is more powerful than even advocates of orthodox Darwinism had believed. Scientists have found that, in some species, observable evolutionary change can take place in as little as ten years. Scientists studying North American fruit flies have recently discovered that flies that migrated to different parts of the hemisphere evolved differences in wing length in only a decade. Furthermore, the differences in wing length matched those of flies that lived under corresponding climatic conditions in Europe.
It has also been discovered that speciation--the creation of new species--does not always happen in the manner that most evolutionary biologists thought it did. It had previously been thought that new species evolved when part of a population became geographically isolated. Since the two subpopulations could no longer interbreed, they would, it was assumed, evolve in different directions. However, biologists conducting field studies have recently discovered that populations that are not separated by geographical barriers often split into two different species by adapting themselves to different environments. This has been observed, for example, in stickleback fish living in Canadian lakes. In a number of different locations, similar but distinct species evolved when some of the fish continued to swim in open water, while others became bottom dwellers.
Finally, contrary to what had previously been thought, it appears that evolution does not invariably take place through the gradual accumulation of numerous small, favorable mutations. It has been shown that sometimes new species are created when a small number of genetic mutations have large effects. This has been seen, for example, in fruit flies on an archipelago in the Indian Ocean and in monkey flowers growing in California. Some of these discoveries are so recent that it is not clear what their implications will be. But if I had to make a guess, I would say that ten years from now evolutionary biologists will still be arguing, most likely about different things. New evidence about evolution is accumulating. Some of it is so surprising that it is likely that new theories will have to be developed to explain it. And theories are something to argue about.
Scientific controversy, though it may be bitter at times, is a healthy thing. It is a sign that scientists are questioning old ideas and looking for ways to better understand existing evidence. Scientific controversy is a sign of vitality. No scientific controversy in a scientific field is a sure sign that few further advances will be made. For example, no one argues about planetary motion anymore, or about how a lens focuses light. The significant questions about those matters were settled long ago, and there is nothing more to add.
Science, in other words, is a quest for knowledge. And when new discoveries are made, it is only natural that scientists should argue with one another about what they have found.