Tuesday, January 04, 2011

On the Evidence for Evolution (1): Richard Dawkins

In 1966, I was in my junior year at Big Spring High School in Big Spring, Texas. Knowing that I would be taking a course in biology, I prepared for the class by studying all the arguments against the theory of evolution and in favor of Biblical creationism. As I sat in the class, I waited for the day when the teacher would bring up the topic of evolution so that I could show off how smart I was by exposing the false claims of evolutionary theory. When we reached the last few weeks of the class, I became agitated because the teacher had said nothing about evolution. Finally, I questioned him in class about when we would be discussing evolution, he responded with some evasive remarks about how there might not be enough time to discuss evolution. I talked with him after class, and I discovered that like many high school biology teachers in Texas, he was afraid to bring up the topic of evolution because it was too controversial with parents.

A few years later, I changed my mind when I decided that the evidence for evolution was plausible enough to be convincing. But I still believed--and believe today--that high school students and college students should be allowed in their biology classes to weigh the evidence for and against evolution by reading some of Darwin's writings, some of the contemporary writing of evolutionary theorists, and some of the critical writing coming from proponents of creationism and intelligent design theory as alternatives to evolution. So here I agree with those proponents of intelligent design theory (particularly, those at the Discovery Institute) who argue for "teaching the controversy" in high school biology classes. But I believe that if students are permitted to make up their own minds after a fair presentation of the debate, most of them will see that the weight of the evidence and the arguments favors evolutionary theory.

One good book for this purpose would be Richard Dawkins' The Greatest Show on Earth: The Evidence for Evolution (Free Press, 2009). Dawkins surveys ten lines of evidence for evolution that should be considered in any debate over evolutionary theory. But while Dawkins himself doesn't believe in "teaching the controversy," his book shows that one cannot properly judge the truth of evolution without comparing it with the alternatives. One should also see the defects in Dawkins' presentation of evolution, insofar as he ignores or plays down some of the most important lines of evolutionary thought.

Dawkins rightly indicates that the theory of evolution--like any scientific theory--cannot be proven in a demonstrative way, as we prove a mathematical theorem as a conclusion that follows necessarily from axiomatic principles. The best we can hope for is to prove it "beyond a reasonable doubt." The biggest problem is that most evolutionary change has occurred in the distant past, and therefore it's not open to direct eye-witness observation. We are like detectives who to the scene of a crime after it has been committed, and we must look for evidence that will allow us to infer what happened. There are at least ten kinds of such evidence for evolution.

(1) Artificial selection and natural selection.
Like Darwin in The Origin of Species, Dawkins begins with the evidence from the human domestication of plants and animals. The history of human beings breeding plants and animals for human purposes shows evolutionary change from artificial selection. This is not just an analogy for natural selection but an experimental test of Darwin's claim that heritable variation open to selective pressures will produce evolutionary change(66).

Dawkins does not acknowledge one problem with the argument from human breeding: although the human domestication of plants and animals shows something like microevolution, it's not clear that this shows macroevolution. The various breeds of dogs are very different from one another, but they are all members of the same species.

Of course, natural selection does not show the intentional design present in human breeding, but natural selection can work through animals acting as selective breeders. For example, insects have created brightly colored flowers by selective breeding through their behavior in cross-pollinating plants; and some females have exercised sexual selection in selectively breeding with those males that are most attractive to them.

(2) Evolutionary clocks.
Evolutionary history must extend over millions or even billions of years, and therefore it's crucial to have techniques for measuring such long time scales. Dawkins explains how various kinds of evolutionary clocks--tree-ring clocks, radioactive clocks, and molecular clocks--provide the necessary measurement for evolutionary time. If one agrees with the Biblical creationists that everything was created about 6,000 years ago, then one would have to refute the accuracy of these evolutionary clocks.

(3) Natural selection in the wild and in the lab.
Richard Lenski has shown how bacteria (E. coli) can evolve in the laboratory. John Endler has shown how wild guppies in Trinidad can evolve in different environmental conditions. For Dawkins, these are examples of evolution in action--evolution that we can actually observe directly.

Again, however, we have the problem that this seems to show microevolution (evolutionary change within a species) but not macroevolution (evolutionary change from one species to another). The assumption that the small changes of microevolution can eventually add up to the large changes of macroevolution needs to be proven.

(4) The fossil record.
Because of the conditions required for the creation of fossils, we cannot reasonably expect a complete fossil record of evolutionary history. But so far, nothing in the fossil record as we know it refutes evolutionary theory.

Contrary to the common claim that Darwinian evolution is unfalsifiable, Darwin's theory could by falsified by finding fossils indicating the appearance of life forms earlier than would be possible by evolution. For example, if we found fossils of mammalian life in the Cambrian period (500 million years ago) or earlier, that would refute the theory. So far, no such fossils have ever been found.

Despite the common talk about "missing links," there are lots of fossils showing intermediate links in evolutionary history. For example, Neil Shubin's discovery of Tiktaalik looks like the perfect link between fish and amphibians.

(5) The human fossil record.
When Darwin wrote The Origin of Species in 1859, there were no ancestral human fossils. But in The Descent of Man, Darwin predicted that earliest human fossils would be found in Africa. This prediction has been confirmed. The human fossil record has grown so that now we have an impressive record of human ancestry from Australopithecus africanus to Homo habilis to Homo erectus to Homo sapiens that allows us to trace the evolution of crucial human traits such as bipedal gait and large cranial capacity.

(6) Evolutionary embryology.
To fully understand evolution, we would have to understand how evolutionary changes have worked through changes in embryological development. Although our knowledge of this is still severely limited, we are beginning to understand how living beings grow through self-assembly. Dawkins stresses that "it's all done by individual cells obeying local rules" as opposed to top-down design through global rules.

How the natural selection of genes controls embryology is still mysterious in practice, Dawkins says, but not in principle. Here is where Dawkins should have said more about the ideas coming out of evolutionary developmental biology (see below).

(7) Geographical distribution.
A likely crucial factor for macroevolution is that two populations within a species become isolated from one another long enough so that when reunited, they cannot interbreed and thus become separate species. The clearest example of this is geographical isolation.

Darwin's studies of the flora and fauna of the Galapagos islands are rightly famous in suggesting how species become adapted to different geographic areas. The diversity of species across the islands and the similarities to species on the South American mainland suggest that species from the mainland migrated to the islands and then radiated out across the islands. That we see many species that are unique to the Galapagos and yet similar to those on the mainland suggest evolutionary adaptation.

It's hard to understand how creationism or intelligent design theory could offer more plausible explanations. If all species originally came from Noah's Ark on Mt. Ararat, why did certain species go to the Galapagos islands and not go anywhere else? The same question could be raised about species unique to Madagascar or Australia.

The well-grounded theory of continental drift or plate tectonics explains how species could have been isolated geographically and then adapted to their locations.

(8) Patterns of resemblance in the tree of life.
The living world shows patterns of resemblance that show a family tree of evolutionary descent. So, for example, the skeletons of all mammals show the same fundamental pattern, although their individual bones are different. On the other hand, no mammals have feathers.

As an alternative explanation, we might say that the patterns of resemblance show recurrent themes in the mind of the Creator or Intelligent Designer. But if the Designer regards feathers as such a good idea, why don't mammals have them?

Advancing knowledge in genetic science now allow us to trace the genetic evidence for common ancestry. If chimpanzees and bonobos are our closest living relatives, as evolutionary science claims, then there should be a very close genetic similarity, and indeed there is.

(9) Historical vestiges of evolution.
If evolutionary theory is correct, we should see "design flaws" that reflect the vagaries of evolutionary history, which we would not expect to see if we thought it was all the work of an intelligent designer. In fact, we see some birds with wings that cannot fly and salamanders with eyes that cannot see. Vestigial wings and vestigial eyes are evidence of evolutionary history in which animal species have undergone awkward adjustments to evolutionary change.

(10) Evolutionary arms races.
If evolutionary theory is correct, we should expect to see organisms competing for scarce resources in ways that do not always promote the collective welfare of the whole ecosystem. And, indeed, we see such costly competition--for example, predators and prey competing in runaway "arms races" where every defensive maneuver of the prey species is followed by an offensive maneuver of the predator species. The costliness of such arrangements and the massive suffering produced by this war of nature is hard to explain as the product of a beneficent designer.

Weighing the persuasiveness of these ten lines of evidence for the theory of evolution depends on the comparative persuasiveness of alternative theories. That's why I think we need to see the fundamental controversy.

As far as I can tell, most of the leading proponents of evolutionary science today--including Dawkins--reject the idea of "teaching the controversy" by allowing students to weight the evidence for evolution against the evidence for creation or intelligent design. After all, they insist, there really is no controversy, because evolutionary science is generally accepted by scientists, and the scientific disputes over evolution are not really about the general theory.

By contrast, I have argued--here and here--that we cannot teach the science of evolution if we don't teach the controversy. If we teach students to simply memorize the concepts of evolution without critically questioning the evidence and arguments supporting those concepts, then we conveying the thought that science is a matter of dogmatic belief rather than reasoned debate.

We can see this in the writing both of Darwin and of Dawkins. Throughout the Origin of Species and The Descent of Man, Darwin compares his "theory of natural selection" with the "theory of special creation" in arguing that his theory is more plausible by comparison. Although Dawkins refuses to specifically cite the authors and texts of creationist and intelligent design theory, he repeatedly in his book shows how the evidence for evolution is most persuasive when compared with what would be predicted by creationism or intelligent design theory.

If students were allowed to actually read some of the writing for creationism and intelligent design, they could critically judge Dawkins' claims. For example, they might notice that Michael Behe--a biologist supporting intelligent design--actually accepts the genetic evidence for common evolutionary ancestry, including the primate ancestry of human beings. Moreover, they might also notice that according to Behe, we cannot know whether the intelligent designer is "a dope, a demon, or a deity." Students might also see that Behe ridicules the idea of taking the Bible as a science textbook. The students might conclude that Dawkins is employing a crude rhetoric of distortion that does not confront the true complexity of the intelligent design position. (Some of my posts on Behe can be found here and here.)

If the students were allowed to do some reading in evolutionary theory beyond Dawkins that might notice that he ignores or plays down many of the lines of research that are becoming prominent today among evolutionary theorists.

(1) Moral evolution.
As I indicated in my previous post yesterday, Dawkins has generally insisted throughout his career that morality cannot be explained by evolutionary science, and therefore that the most important features of human life are beyond natural science. But in making this argument, he rejects Darwin's ethical theory in The Descent of Man.

Most recently, however, Dawkins' endorsement of Sam Harris's The Moral Landscape suggests that Dawkins has changed his mind and that he is now following the lead of other evolutionary theorists who are working on evolutionary explanations of human morality.

(2) Epigenetic evolution.
Like other Neo-Darwinians in the tradition of the "Modern Synthesis" of evolutionary biology, Dawkins assumes that genes are the only units of selection and that there is no Lamarckian inheritance of acquired characters. In recent years, this Modern Synthesis has been thrown into doubt. In particular, there is growing recognition of epigenetic mechanisms that allow for Lamarckian evolution. This has been the subject of a previous post. Dawkins is scornful of the idea of epigenetic evolution, which he dismisses in a footnote (216). Actually, the recent recognition of epigenetic evolution is a return to Darwin, who saw the importance of Lamarckian evolution.

(3) Gene-culture coevolution.
Some of the most important research in evolutionary theory--particularly as applied to human beings--is in understanding the evolutionary interaction of genes and culture. This is also a return to Darwin. Although he did not understand genetics, he did understand the importance of culture evolution as interacting with innate predispositions. Some of my posts on this can be found here and here.

Although Dawkins originated the idea of "memes" as units of cultural evolution, he mentions this only briefly in this latest book (406-408).

(4) Group selection.
As the proponent of the "selfish genes" theory of evolution, Dawkins is a vehement opponent of group selection--the idea that evolutionary selection can occur at the level of groups. Dawkins denies that Darwin endorsed group selection, but this is clearly wrong (62, 390, 393). In The Descent of Man, Darwin emphasized the importance of group-against-group competition in evolutionary history. Recent work by David Sloan Wilson and E. O. Wilson has confirmed that Darwin was right about this.

Posts on this topic can be found here, here, and here.

(5) Evo Devo.
In recent decades, some evolutionary theorists have become ever more skeptical that the Neo-Darwinian Modern Synthesis can explain how the mechanisms of microevolution lead to the macroevolution of new species. As an alternative, there is growing interest in evolutionary developmental biology--"Evo Devo"--as perhaps providing a new set of explanations. We need to understand how regulatory genes during embryonic development turn the other genes on and off at different times and places in the body, and how evolutionary change in these "genetic switches" might account for macroevolution. This has been the subject of a previous post.

Dawkins implicitly recognizes the importance of this research when he talks about "the evolution of evolvability" as a property of embryologies (423-24). But, remarkably, he does not explicitly speak of this as Evo Devo or cite any of the leading exponents, such as Sean Carroll.

(6) Religion.
As a vehement atheist, Dawkins has no interest in considering how evolutionary theory and religious belief might be compatible. He does at least acknowledge that some Christians--including some Anglican and Catholic bishops--have collaborated with him in writing some public statements endorsing evolution, and he thus recognizes the possibility of theistic evolution in which God uses the evolutionary process to execute his will. But it's impossible for Dawkins to take this seriously (5-6). Similarly, he cannot take seriously Darwin's conception of the Creator as the source of the natural laws underlying evolution and as the original source of matter, energy, and life (403-404). Dawkins refuses to admit that even if Darwin was not an orthodox Christian, Darwin was open to the possibility of God as the ultimate ground of natural order.

Moreover, Dawkins has nothing to say about the recent research on the evolutionary origins of religious belief, which supports my claim that there is an evolved natural desire for religious understanding. Links to some of my previous posts on this can be found here.

If students were allowed to actually read Darwin in their biology courses, they might notice that most of this new research in evolutionary science is reviving ideas that were already there in Darwin's writings, which confirms the thought that although there has been much progress in evolutionary science since Darwin wrote, no one has surpassed his genius in anticipating most of the major insights in evolutionary reasoning.

1 comment:

Troy Camplin said...

Self-Organization. The issue of the emergence of complexity seems to be central to the complaints against evolution. Self-organizing processes as natural and spontaneous is the only real answer to those questions. And I have found this to be an answer that cannot be answered.