Short Shrift to Evolution?

Editor's Note: In this essay, the authors--both scientists and writers--discuss recent news stories on evolution and express their opinions on how the stories were handled by the mainstream press. Evolution took center stage at the National Association of Biology Teachers (NABT) annual meeting in Reno, Nev., Nov. 3-8, 1998. If the teachers needed a theme, evolution was a logical choice--after all, it underlies and unifies contemporary biology. But NABT had other fish to fry. Despite a spate of court victories, evolution hasn't made much, if any, headway with the public. And many high school teachers apparently aren't aware of its centrality to the discipline, or they feel too intimidated to stress its importance in biology. With a recent National Academy of Sciences (NAS) report, "Teaching About Evolution and the Nature of Science"1 for focus, NABT rallied the troops. Also in attendance was New York Times reporter Jon Christensen, who solicited comments about the evolution theme on the message board. Christensen's Nov. 24 story, "Teachers Fight for Darwin's Place in U.S. Classrooms,"2 captured biologists' frustration, mixing attendees' comments with accounts of meeting sessions. But he didn't say why the NAS and NABT think teaching evolution is so important. When asked about the omission, Christensen said, "I wasn't able to cover everything that I might have liked to cover in my story." Instead, with only a modicum of science, and anecdotes carefully chosen to paint a particular portrait, the story gave the impression that evolution is still so iffy that biologists could reasonably disagree on its validity. The impression was reinforced on Dec. 1 when the Times's Gina Kolata began a supposed news story with the hardly objective statement, "Evolutionary biology can be long on theory and short on evidence."3 Christensen offered several shopworn examples of evolutionary evidence such as antibiotic and pesticide resistance, and managed to tip his hat to the Human Genome Project. But, he needed only to have picked up any recent life science journal to see the vast and ongoing supply of data supporting evolution. By not relaying the strength of evolution as a scientific principle, his story made evolution seem like just one more thing to fight about. Nothing could be farther from the truth. There is no real debate among life scientists about the central role of evolution in the field. Supposed challenges are largely rhetorical and contain arguments from ignorance (we don't understand everything about evolution, so it must be wrong). The alternative to evolution is supernatural, most recently incarnated as "intelligent design theory." Much of the argument boils down to the nature of science, a second theme of the NAS report. Can the objective, material methods of science be used to investigate the supernatural? Most scientists say no; therefore, attempting to cloak "intelligent design" and the like in the attire of bona fide science is silly and pernicious. But evolution prevails by more than default. As a scientific fact or theory, it's incredibly robust--the evidence is accumulating faster than most of us can assimilate it. Like the recently discovered square mile of Patagonia covered with sauropod eggshells so numerous that paleontologists cannot sidestep them,4 the footprints of evolution are everywhere and unavoidable. To illustrate the pervasive impact of evolution on life science research, we thought it would be worthwhile to survey recent issues of the journals Nature and Science. We start with an ecological study that directly links plant biodiversity to the kinds of mycorrhizal fungi associated with their roots.5 The fungi aid uptake of phosphorus and other elements, and provide pathways for plants to exchange carbon. That is, fungi are crucial in the function of terrestrial ecosystems. But that provokes the question of how these relationships were established. The historical record in the form of fossils and gene sequences shows that fungi were probably partners of the first plants more than 400 million years ago, and were important for their success on land.6,7 Clearly, ecology is inextricably tied to evolution. To paraphrase noted geneticist Theodosius Dobzhansky, nothing in biology makes sense, except in the light of evolution. The next week's Nature offered the genome sequence of Rickettsia prowazekii, the bacterium that causes typhus.8 Knowing the sequence provides ammunition to fight this serious disease, but once again, evolutionary implications shine through. The Rickettsia genome more closely resembles that of mitochondria than other bacteria studied so far, providing important clues to the microbial origin of mitochondria. This discovery strengthens the endosymbiont theory, which predicts that some bacteria would be more closely related to mitochondria than others, and that genetic control of organelle function was progressively ceded to the nucleus (the evolutionary implications were also discussed in news articles in Nature and the Nov. 13 Science ). Interestingly, the theory also predicts that some mitochondria are more closely related to bacteria than others. Work with a protozoan called Reclinomonas confirmed that prediction last year.9 When we sequence genomes, from organisms as diverse as Rickettsia and humans, often in search of useful genes, evolution sticks out like a tree in the Sahara. The Nov. 12 issue of Nature also reported on glutamate receptors, important signal molecules that function in nerve transmission in animals.10 As it turns out, plants also have these proteins, and they are strikingly similar to their animal counterparts in gene sequence and predicted 3-D structure. The plant receptors are involved in signaling too, in response to light. The link between animal and plant kingdoms in signal transduction grew stronger yet in the Nov. 20 issue of Science. The cryptochromes are photoreceptors responsible for initiating a number of growth and developmental responses including phototropism, the turning of plant shoots toward light. Cryptochromes also help set the circadian clock, in Arabidopsis and probably other plants.11 But nature grew even more fascinating in the following paper--cryptochromes are also present in humans and mice, where they regulate the clock!12 One of the Arabidopsis cryptochromes has been expressed in insect cells where it acts as an autophosphorylating kinase consistent with its role as a photoreceptor.13 And diverting for a moment to the journal Cell, we find two reports on cryptochromes in Drosophila, where they are again blue light photoreceptors with an integral link to biological clocks.14, 15 The evolutionary implications of glutamate receptors and cryptochromes are unavoidable. Convergent evolution may account for some similarities, but plants and animals also inherited genes from a common ancestor(s) which, like any other biological entity, responded to its environment. And that common ancestor obtained them in a continuous evolutionary process dating back to the origin of life. Supported by a wealth of other data, it's the simplest and most scientifically logical explanation of why disparate organisms share similar genes. Is the message not getting through, or do people not want to hear it? This is only a sample of relevant articles from a scant few weeks. On the other hand, we found no papers offering objective, material evidence in favor of intelligent design or any other supernatural explanation of plant diversity, mitochondrial origins, glutamate receptors, cryptochromes, or any other biological structure or process. That's one of the reasons why invoking supernatural intervention is, as director of the center for cognitive studies at Tufts University Daniel Dennett likes to say, a skyhook that is not only cumbersome but scientifically untenable.16 Yet the public remains untouched by the evolutionary implications that pervade the scientific literature but less frequently penetrate the popular press. Widely read newspaper accounts that exaggerate the degree of disagreement within the biology community do not help matters. And the problem isn't that Jane and John Doe haven't heard about the impact of DNA evidence. In addition to O.J. Simpson's trial and Bill Clinton's encounter with Monica Lewinsky's blue dress, the recent report that Thomas Jefferson probably fathered a child by his slave Sally Hemmings predictably hit the media in a way that the typhus genome implications never would. The Jefferson case was made through a systematic search of historical records combined with the tools of molecular genetics.17 If people are willing to accept such evidence to prove family genealogy 200 years removed, why not evolution over millions of years? The concepts and tools are essentially the same. It is unrealistic to expect every high school biology teacher to follow the latest developments in the pages of Science and Nature, let alone the many more specialized scientific journals. Still, the scientific community can do a better job relaying the robustness of evolution and its centrality to modern biology to people who play such an important role in the education of our children. The NAS report should be part of a continual stream of information geared to teachers, and steps should be taken to assure that the stream gets through. As Susan Epperson, plaintiff in a landmark U.S. Supreme Court decision (Epperson v. Arkansas) noted, "I would like to see the NAS booklet put into the hands of every biology teacher." We realize that resistance to evolution stems from religious convictions--in the end, people will believe what they want. But at least students and teachers should be aware of the strength of science's case. Barry A. Palevitz (palevitz@dogwood.botany.uga.edu) is a professor of botany at the University of Georgia. Ricki Lewis (rickilewis@nasw.org) is a textbook author and a contributing editor for The Scientist. Teaching About Evolution and the Nature of Science, Washington, D.C., National Academy Press, 1998. (Full text available online at www.nap.edu/readingroom/books/evolution98/) J. Christensen, "Teachers fight for Darwin's place in U.S. classrooms," The New York Times, Nov. 24, 1998, p. F3. G. Kolata, "Mice fail to verify an evolutionary theory," The New York Times, Dec. 1, 1998, p. F2. L.M. Chiappe et al., "Sauropod dinosaur embryos from the Late Cretaceous of Patagonia," Nature, 396:258-61, Nov. 19, 1998. M.G.A. van der Heijden et al., "Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity," Nature, 396:69-72, Nov. 5, 1998. L. Simon et al., "Origin and diversification of endomycorrhizal fungi and coincidence with vascular land plants," Nature, 363:67-9, 1993. W. Remy et al., "Four hundred-million-year-old vesicular arbuscular mycorrhizae," Proceedings of the National Academy of Sciences, 91:11841-3, 1994. S.G.E. Andersson et al., "The genome sequence of Rickettsia prowazekii and the origin of mitochondria," Nature, 396:133-40, Nov. 12, 1998. B.F. Lang, "An ancestral mitochondrial DNA resembling a eubacterial genome in miniature," Nature, 387:493-7, 1997. H.M. Lam et al., "Glutamate-receptor genes in plants," Nature 396:125-6, Nov. 12, 1998. D.E. Somers et al., "Phytochrome and cryptochromes in the entrainment of the Arabidopsis circadian clock," Science, 282:1488-90, Nov. 20, 1998. R.J. Thresher et al., "Role of mouse cryptochrome blue-light photoreceptor in circadian photoresponses," Science, 282:1490-4, Nov. 20, 1998. J.M. Christie et al., " Arabidopsis NPH1: A flavoprotein with the properties of a photoreceptor for phototropism," Science, 282:1698-1701, Nov. 27, 1998. P. Emery et al., "CRY, a Drosophila clock and light-regulated cryptochrome, is a major contributor to circadian rhythm resetting and photosensitivity," Cell, 95:669-79, Nov. 25, 1998. R. Stanewsky et al., "The CRYb mutation identifies cryptochrome as a circadian photoreceptor in Drosophila," Cell, 95:681-92, Nov. 25, 1998. D. Dennett, Darwin's Dangerous Idea--Evolution and the Meanings of Life , New York, Simon & Schuster, 1995. E.A. Foster et al., "Jefferson Fathered Slave's Last Child," Nature, 396:27-8, Nov. 5, 1998.

Short Shrift to Evolution?

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