Is There an Edge to Evolution? Part 3
In his previous post, Dr. Ussery showed that Behe’s analysis of the probability of getting beneficial mutations is flawed at fundamental levels. Beneficial mutations do occur, new genes do evolve and he cited some research articles that demonstrate this and then showed the interested reader how to gain access to the vast scientific literature that exists. He expresses concern that Michael Behe has not chosen to make the general public aware of what is being done in this arena.
In today’s post he goes on to examine what Behe states is the limit of what Darwinian evolution can and cannot do.
Chapter 4 - What Darwinism Can Do
The title for this chapter is a bit deceptive, in that most of this chapter is not really about what evolution CAN do, but rather what the limits to evolution are (the topic for the next chapter). There is a short description of genome sequence analysis and the types of mutations observed in the laboratory, but in my opinion this chapter is really missing a thorough discussion of the astounding variety and diversity we find when we examine genomes.
Again, Behe emphasizes that he has no problem with evolution by common descent:
Over the next few sections I'll show some of the newest evidence from studies of DNA that convinces most scientists, including myself, that one leg of Darwin's theory - common descent - is correct. (page 65).
Once again, the problem is random mutations:
The bottom line is this. Common descent is true; yet the explanation of common descent – even the common descent of humans and chimps – although fascinating, is in a profound sense trivial. It says merely that commonalities were there from the start, present in a common ancestor. It does not even begin to explain where those commonalities come from, or how humans subsequently acquired remarkable differences. Something nonrandom must account for the common descent of life. (page 65, emphasis in the original).
I absolutely agree with Behe – there must be a ‘non-random’ account. But I’m a bit confused here, because natural selection is, by definition, definitely non-random. That’s the whole point! There is (random) variation, and then those variants that are better are selected. It is not at all random. But Behe’s claim here is that there are not enough random variants produced for evolution to occur. 150 years ago, at the time of Darwin’s writing, it was not known whether the variation was random or produced in some other manner – and in a sense this did not matter.
What was important for Darwin was that the variation was there, and that the method for non-random selection – also known as “natural selection” – could account for the non-random common descent of life. One of the analogies Darwin used was “artificial selection”, where, for example, dog breeders would breed certain traits, giving rise to a large variety of dogs within a short amount of time – merely by [non-randomly] selecting for desired traits. Darwin reasoned if this worked for breeders, why couldn’t it work in natural environments? And as far as “random variations” go, we have quite a bit of variance in dogs, from tiny toy poodles to St. Bernards.
More than half the chapter is devoted to species that have had duplications of their entire genome. Behe focuses especially on yeast, although he mentions in a footnote that other whole genome duplications have been documented. But again, the text written is more within the framework of the limits of evolution—what it can’t do, which should be the subject for the next chapter (I suspect a chapter strictly about what Behe thought evolution could do would be quite thin). The claim that “genome duplication…. has not given baker’s yeast any advantage it wouldn’t otherwise have had” (page 74) seems pretty harsh, especially now that more than two dozen different strains of yeast have been sequenced, and there are clear advantages in survival associated with duplication of many of these genes.
Perhaps, once again, Behe is not familiar with the literature and not willing to have a look at what has been published. I encourage the interested reader to go ahead and have a look at what is out there—go to PubMed, and type in the words “yeast genome duplication evolution” and have a look at the articles found. Today when I did this, I found 420 articles. The second one on the list has this statement in the concluding sentence of the abstract: “Our results provide a scenario for how evolution like a tinker exploits pre-existing materials of a conserved post-transcriptional regulon to regulate gene expression for novel functional roles.” Behe concludes the chapter by saying that “although Darwin hoped otherwise, random variation doesn't explain the most basic features of biology” (page 83).
For more on what evolution CAN do, I mention “The Edge of Evolution” in a footnote in the last chapter (Evolution of Microbial Communities) of my textbook on Comparative Genomics. It is in a section on “Where Does Diversity Come From?”, and I make the statement that some anti-evolutionists “claim that there is not enough diversity in bacterial populations for evolution to occur.” I encourage the interested reader to have a look at this section, as I think it is a nice culmination of a story I’ve slowly built up through the previous chapters on bacterial genomics.
I readily admit that this is something that takes time to understand and cannot easily be explained in a 10-second sound bite – this textbook came from a course I’ve taught at the Technical University of Denmark since 2000. Currently the course meets in the autumn semester, for 8 hours a week, for 13 weeks; this year I have 54 students. So this takes time to explain, but my point here is that the claim that nothing has changed over the past 10 years, in terms of evidence for evolution and documented diversity, is simply wrong.
Chapter 5 - What Darwinism Can't Do
The title of this chapter reminds me of a book by Lenny Moss, called What Gene’s Can’t Do. I think this is a wonderful book, kind of countering the “gene-centric” popular culture. It’s a well-written book, and in my opinion he makes some valid scientific points. Unfortunately, although Behe could have had a similar good discussion here, instead we are treated to poor quality left-overs. This chapter is kind of an update on “irreducible complexity” as outlined in Behe's previous book, Darwin's Black Box. In spite of strong protestations from many (including myself) in their reviews of that work, Behe still clings to the idea that no one has ever published anything about the evolution of these complex molecular machines. “Despite the amazing advance of molecular biology as a whole, despite the sequencing of hundreds of entire genomes and other leaps in knowledge, despite the provocation of Darwin's Black Box itself, in the more than ten years since I pointed out that a situation concerning missing Darwinian explanations for the evolution of the cilium is utterly unchanged” (page 95).
Again, the interested reader is invited to visit PubMed, type in “cilium evolution” and see for oneself: are we to believe that articles with titles like “The evolution of the cilium and the eukaryotic cell” and 'Origin of the cilium: novel approaches to examine a centriolar evolution hypothesis” simply don't exist? Perhaps if one closes their eyes, and clicks their heels three times, thinking, “They don't exist, they don't exist”, maybe these articles can simply vanish!
Last week I gave a lecture in my course about the 10th anniversary of sequencing the human genome. In the field of genomics, much has happened in the past 10 years. There has been an explosion in the amount of genomic data available, and also in the strong, clear evidence for evolution in exactly the manner Behe claims is impossible and will never happen. To put this in perspective – when I first came to the Center for Biological Sequence Analysis in 1997, there were four bacterial genomes sequenced. Last week, in my course I showed an update of the currently sequenced genomes: there are now more than four thousand genomes sequenced, and the number is growing on a daily basis. And the more genomes we sequence, the more we learn about how evolution works. When I was growing up, the preacher in our church used to say, “Did you hear about the guy who said ‘It can’t be done?’ Well he got run over by the guy doing it!” I think there is some truth in this – Behe says it can’t be done, and a decade later, despite this vast amount of data, he claims things remain “utterly unchanged”.
In my next post, I will examine Behe’s discussion of whether random mutation hitched to natural selection is a biological explanation for various molecular phenomena.
David Ussery is an associate professor of comparative microbial genomics at the Center for Biological Sequence Analysis at the Technical University of Denmark and on the faculty at the University in Oslo, Norway. Ussery is the co-author of Computing for Comparative Microbial Genomics and has authored or co-authored 130 articles for science and professional journals. He is also a frequent public speaker on the topic of bacterial genomics.