The Problem With Evolution: Where Have We Gone Wrong?

To paraphrase Theodosius Dobzhansky, nearly everything we study in biology makes sense only in the context of one central unifying concept: evolution. Yet evolution is still quite "controversial," as a recent article and letter in this publication demonstrated (R. Lewis, The Scientist, May 12, 1997, page 13; M.J. Behe, The Scientist, June 9, 1997, page 10). Many people are still convinced it never happened. How is it that so many scientists can claim something is so certain, and so many people can be so sure it's wrong? Why can't scientists "show" the public the "truth"? We're often tempted to blame it on "them"-these "zealots" who reject evolution, who have been so blinded, their minds so closed to the truth, that nothing we can do will sway them. But, in truth, we can't lay the blame so easily. As scientists and teachers, we've dropped the ball. Many of us don't even try to teach evolution, or we just put it out there without trying to engage the students, for fear we'll open a Pandora's box that we won't be able to close or that we'll be out in territory we don't think we can adequately defend. In arguing with the students on this point, we might risk looking like we don't know it all. Indeed, many of us have holes in our understanding of evolution, and even doubts, because we too have been taught by people who were afraid of the topic. I myself am guilty. I've often taught evolution of genes, avoiding the actual topic of evolution of species or humans, because teaching at a religiously linked Southern college, I knew I'd have a tough time with it. I'd like to share a few of the tools I use to attempt to clarify the controversy to my students. One of the major problems with our understanding of evolution is how we define it. "Evolution" and "natural selection" are terms used to explain the origin of the universe and of life on Earth, as well as processes in business, behavior, product development, and more. There is no consensus of the term's meaning even among biologists and authors of biology texts (see Y. Linhart, Bioscience, 47[6]:385, 1997), which certainly adds to the confusion. In his letter to The Scientist, Michael Behe points out there are three aspects to the term "evolution." Unfortunately, the word is used in far more than three different ways. The solution suggested by Linhart and others is to use the term evolution as broadly as possible; I believe we must limit its use to one. "Evolution," in the context most biologists intend to use it, is correctly defined simply as "descent with modification." That's the way Darwin introduced it, and that's the way in which it is basically incontrovertible. Darwin argued that species were created from other species through a process of change over time, by natural selection. Period. It's important to note that Darwin did not comment on the origin of life, and we need to stop linking the concept of the biochemical origin of life with the term "evolution." They are clearly two different phenomena. The fact is, we have very little real, tangible evidence that supports the prevailing hypothesis of how life originated. And even if we could prove it possible, we can't go back and see how life actually originated. But we have much solid evidence demonstrating that all the life forms we've studied on this planet arose from a single common ancestor, changing and diversifying over billions of years. Contrary to Behe's claim, the genetic evidence for common ancestry, up to and including humans, is overwhelming. Many critics point to the lack of evidence for the "evolutionary theory" of the origin of life and say, "See! The theory of evolution is an unsubstantiated theory!" And if we make the mistake of grouping the origin of life in with "evolution," it's hard to argue otherwise. The evidence for evolution is often complex and difficult to understand, and we often don't take the time or trouble to try to make it understandable. The genetic evidence for evolution is perhaps the best example. I think the genetic similarities (and differences) between DNA sequences of different species is the best evidence we have, but it's difficult to explain to college students who have never sequenced DNA. I'd like to take a shot at simplifying it by presenting an analogy. Imagine I gave an assignment to my class of 10 students to write a 10,000-word essay on a certain topic. On the due date, I get back 10 identical essays. What could I conclude? The chances that each of the 10 students would come up with the identical essay independently are . . . well, basically zero. It's just not possible. So I know they weren't done independently, but I don't know how they were done. I don't know who wrote the original paper, and who copied from whom. But imagine instead that I get back 10 papers that are almost identical. I get one superb paper from John. James's paper is identical with one exception: Word number 300 is different, and the sentence it's in now makes no sense at all. It seems quite likely that James copied from John (or from someone who copied from John) but made a mistake in word No. 300. Jan's paper is identical to John's, except it has two nonsensical mistakes-the very same mistake at word No. 300, plus another at word No. 1,100. And Susan's paper shares the very same mistakes at words No. 300 and No. 1,100, plus a new one at word No. 124. How would you interpret this? Well first of all, the papers weren't done independently. Even with the few differences, they're far too similar. Could they all have been copied from the same source or all copied directly from John? Unlikely. The chance of Susan and Jan independently making exactly the same mistakes at words No. 300 and No. 1,100 is extremely small. And extending the analysis, the chance of the 10th student independently making exactly the same eight errors as the previous student is basically zero. The only reasonable explanation is that James copied from John, then Jan copied from James, and so forth. Well, the same thing is true when we compare genetic sequences of different organisms. Yes, their DNA is surprisingly similar, but it's the differences-the mistakes (mutations) shared by species believed to be close on the evolutionary tree-that are the most instructive. And we're not talking about just a few instances here; thousands of sequences have been compared in different species. The only reasonable way to interpret these differences is to assume that all the species examined were created from one another, "copied" in a definite order that we can now elucidate. Notice this evidence says nothing about how they were copied, whether by divine intervention or natural selection. But it shows quite definitively that all the species were created along a branching time line, one from another. And although this is a rather simplistic analogy to the genetic sequence evidence, this evidence does indeed demonstrate a serial "copying" of species, up to and including humans. I continue by suggesting to my students that if we define evolution as descent with modification, not only do we know it did happen, but also it seems as if it basically had to! Let's imagine for the moment that there's life on another planet. Of course, right now we have no direct evidence that there is life on any other planet. But let's pretend. Let's imagine the simplest form of life, such as a single-celled organism not very different from our own bacteria perhaps, is living on . . . well, let's say Mars. Would that life "evolve"? To answer that question, we need to ask two others: Would this life form have "variation," and would it have "natural selection"? The first is rather easy. Either there is variation (mutation) or the cells copy themselves perfectly, every single generation, with absolutely no mistakes. Given entropy, that's just not possible! Mistakes are inevitable. True, mistakes might be far less frequent than on Earth, or far more frequent-but they must occur. Given variation, would there be "natural selection" for the fittest organisms? Let's again look at the alternative. The only way the fittest will not outperform the less fit is if there's no competition. In other words, there's an unlimited supply of food, space, and resources to accommodate an unlimited number of offspring. Again, that's not possible. As the population grows, there must come a point when the resources become limited. Thus, there must be competition, and if there's competition, clearly some variants must survive more often or longer than others. That's natural selection. When you put those two together, the inevitability of variation and of eventual competition, you see that so long as life continues to exist on the planet, evolution must occur. This argument says nothing about the rate of evolution or about its direction. It would be extremely unlikely for evolution on another planet to follow any directions similar to those of Earth. There would be no reason to expect humans, or bipeds, or multicellular (or even cellular, for that matter) organisms to evolve. But change, to forms better adapted to their environments, is inevitable. Behe and others claim that there just isn't sufficient time to create such amazingly complex creatures as us in a "mere" 3 billion or so years. But what's the basis for such a claim? Just that we can't yet "prove" that 3 billion years could have been enough time and that it seems to be contrary to the common sense of creatures who live less than one 10-millionth that long. On the contrary, in the face of such overwhelming evidence that evolution did occur, the burden of proof is on the skeptics to demonstrate that life could not have evolved in such a "short" time. Descent with modification, the theory that all forms of life on Earth are related by having a common ancestor that changed and diversified over time, is backed by such a wealth and diversity of evidence that all but a few scientists accept it with great confidence. There is virtually no possibility that the "theory" of evolution is not true; however, there are still many open questions about how evolution works. There's a big difference here, which we need to communicate to our students and to the public. Disagreements about how evolution occurs by many reputable scientists should not be taken as disagreement on whether it occurred. There's little doubt on that point, despite the power of a few vocal opponents to suggest otherwise. The ball is in our court. Scientists and teachers must begin taking the offensive on evolution, discussing and educating, intelligently and openly. And to do that, we've all got to be on the same playing field, referring to evolution as the same thing. Otherwise, we cannot reach scientific literacy as a society. Robert Moss is an associate professor of biology at Wofford College in Spartanburg, S.C. E-mail: MOSSRE@WOFFORD.EDU

The Problem With Evolution: Where Have We Gone Wrong?

Interested in reading more?

Become a Member of