Welcome to an imaginary world of Red Queens, Green Beards and warring armies: the world of evolutionary theory. Though its adherents work in prestigious universities and laboratories in the real world, they seem preoccupied with speculative visions of imaginative fitness landscapes – even when defending evolutionary theory as the best explanation for natural phenomena, and essential for our understanding and progress in science. This can be seen in two recent papers, one pro-evolution and one critical of it, that center on the question: is evolutionary theory essential to biology? Ajit Varki defended evolution all the way down in a paper in Cell1 with the self-explanatory title, “Nothing in Glycobiology Makes Sense, except in the Light of Evolution.” Adapting the title from a famous quote by Theodosius Dobzhansky, used more often as a club than a flashlight at school board hearings, Varki attempted to show the utility of evolutionary theory to one specialty: glycobiology, the study of biological sugars. This is a complex field of unity and diversity, complexity and simplicity, conservation and diversification. Cells use sugars inside and outside for a variety of functions, but pathogens also attach to them. Glycobiology seems a confusing picture, from highly-conserved enzymes that have changed little from mouse to human, to variations within species and even within the lifetime of organisms. In his defense of evolution to make sense of it all, he invokes the Red Queen effect (running in place to get nowhere: see 05/16/2004, 03/31/2006), co-evolution and evolutionary arms races. It’s not clear, however, whether his presentation would convince a critic. For one thing, most of his examples deal with microevolution, which is not controversial, even among the most ardent creationists. The only exception is his treatment of possible means of speciation, one species splitting into two – which also fits within most creationist frameworks. Nowhere in his article, however, does he explain how glycobiology needs evolution to explain the major changes most often implied by the term evolution. A critic might also point out that Varki’s ideas are amply sweetened with speculation, by his own admission: “Whatever the reader might think of the speculations in this Essay,” he states in conclusion, “it is safe to suggest that approaches to understanding glycan biology must fully take into account the role of multiple and often simultaneous evolutionary processes, an aspect that has received limited attention.” That seems an admission that many biologists have up till now not given it much attention – a contradiction to Dobzhansky’s claim. It’s noteworthy how many times Varki’s scenarios are salted with qualifiers and peppered with hopes: The question that needs to be asked is not whether evolutionary theory may explain the phenomenon in question, but whether it is essential for any sensible explanation: whether or not “nothing makes sense except in the light of evolution.” A Biblical creationist, for instance, might be perfectly content with certain aspects of these mechanisms at the microevolutionary level – evolutionary arms races and Red Queen effects – in a world cursed by sin and infected with pathogens. He might claim that the Creator provided enough versatility for organisms to be able to adapt to changing environments, so that an animal would not be wiped out by the first encounter. Yet the same creationist would still vehemently deny molecules-to-man evolution, the kind envisioned by Darwin and Dobzhansky. Another assertion left unproved is whether biology really needs the kind of speculation Varki illustrated in its day-to-day business. This question was taken up by a well-known critic of evolution, Jerry Bergman, who investigated whether practicing biologists actually illustrate Dobzhansky’s claim in their work. In a recent article on TrueOrigin, Bergman concluded that Dobzhansky’s claim is a myth. He interviewed scientists and researched textbooks, and found that evolutionary theory was rarely mentioned or used, and when it was, it was more an afterthought than a substantive part of the discussion:If, as Dobzhansky stated, “nothing in biology makes sense except in the light of evolution”…, why is it rarely, if ever, mentioned in most natural science books? We usually use the leading college texts in each area (for example, the A&P text we use is the 10th edition of Hole, a standard text). And why is it a minor topic even in most introductory biology books that cover the subject in more depth than most all other courses except formal classes on evolution?He concluded, “This statement is ideologically not factual. Biology makes perfect sense without ever mentioning Darwinism.” (See also the related entry from 08/30/2006).1Ajit Varki, “Nothing in Glycobiology Makes Sense, except in the Light of Evolution,” Cell, Volume 126, Issue 5, 8 September 2006, Pages 841-845, doi:10.1016/j.cell.2006.08.022.Varki inserted so many doubt-words into his text, it makes you wonder which side of the looking-glass he is on. Despite his valiant effort, he only showed that evolution doesn’t buy you anything in theory. Last week, Jerry Coyne showed (08/30/2006) that evolution doesn’t buy you anything in practice. Conclusion: evolution is a bad investment. While scientific freeloaders amuse themselves with “tantalizing speculations” in the Darwin Party lizard lounges (12/22/2003 commentary), the real work in science is being done by design (e.g., 07/21/2006, 06/29/2006, 06/22/2006).(Visited 58 times, 1 visits today)FacebookTwitterPinterestSave分享0 Overall, one can speculate that some episodes of speciation might be mediated by pathogens that bind to specific forms of cell-surface glycans.A lethal pathogen that binds to glycans of a certain species to initiate infection might markedly reduce the primary population, leaving geographically isolated subpopulations that have the opportunity to evolve into new species.Some of the survivors are likely to have been selected because of random glycan variations that allowed them to escape from infection with the pathogen.Such survivors may have secondary alterations in glycan biology that are permissive for pleiotropic changes in embryogenesis and/or morphogenesis.Glycan changes also might alter fertilization barriers, causing either reproductive isolation or anomalous fertilization by closely related species.Any or all of these mechanisms could support the formation of new species. Many of these speculative ideas are testable by observational studies and possibly by long-term experiments. [No examples cited.]Thus, glycans may be trapped in neverending cycles of evolutionary “Red Queen” effects in which long-lived hosts must evade the more rapidly evolving pathogens that infect them by changing their glycan expression patterns, without compromising their own survival (Van Valen, 1974 and Hamilton et al., 1990). The colorful term, “Red Queen” effect, recalls the comment to Alice by the Red Queen in Lewis Carroll’s Through the Looking Glass that “it takes all the running you can do, to keep in the same place.” This may explain the remarkable structural variations of glycans in nature, which contribute to biological diversity and perhaps even to speciation.Thus, the glycans of complex multicellular organisms with long life cycles may be subject to evolutionary “Red Queen” effects….For example, cell-type-specific expression of certain glycans can mediate specific biological roles within an organism (Lowe and Marth, 2003), which thus may be under positive selection.Additional Red Queen effects may arise from the fact that many pathogens use a successful form of molecular mimicry,…Such diversification and redundancy may be driven by sexual selection and sexual conflict….