Missing Links

Saturday, 22 October 2005 20:12 by: Anonymous

    Missing Links
    By Peter Dizikes
    The Boston Globe

    Sunday 23 October 2005

Proponents of Intelligent Design have exploited a vexing question at the heart of Darwin's theory. Now, say two leading biologists, scientists can - and must - answer back.

    In a federal courtroom last week in Harrisburg, Pa., site of the ongoing trial to decide whether ninth-grade biology students in Dover should be required to hear about Intelligent Design, Michael Behe, a professor of biochemistry at Lehigh University, took the stand. Behe is the originator and main proponent of the term "irreducible complexity," a pillar of Intelligent Design, which refers to the notion that certain organic structures are too intricate to have evolved on their own.

    Virtually all biologists dismiss Behe's claims-indeed, most see Intelligent Design as a claim that research on complex structures is not possible, a position they reject. This is one reason biologists, to the dismay of some of evolution's most vocal supporters, have often ignored the Intelligent Design movement altogether.

    There are clear signs, however, that the looming presence of Intelligent Design has started having a discernible impact on evolutionary scientists. While it may not be driving their research, or dampening their sometimes boisterous internal debates, the public controversy may be forcing biologists of all kinds-and not just evolutionary biologists-to take a wide-angled view of their field, to examine how their current research contributes to evolutionary theory, and to consider how best to present evolution in the public sphere.

    "We shouldn't dismiss questions, even if some are ill-intentioned," says Marc Kirschner, founding chair of the Department of Systems Biology at Harvard Medical School. "But at the same time, we need to realize that science has real answers to these questions."

    YOUR VIEW: Can science answer the claims of creationists? GLOBE GRAPHIC: Plausibly complex

    Far from being restricted to the fossil record, as creationists often imply, research in the last 25 years from molecular biology, genetics, cell biology, and embryology has added greatly to the existing evidence for evolution. "There are all sorts of demonstrations of evolution going on all the time," notes John Gerhart, a biologist at the University of California, Berkeley.

    Even so, Kirschner and Gerhart believe, some biologists and many science-literate general readers-not to mention a larger slice of the public-are unaware of the advances in the field. If Behe, for one, can question evolution, Kirschner and Gerhart contend, biologists have an increasing responsibility not only to explain evolution to the public, but to be fully aware of the evolutionary implications of their own work. ..

    As it happens, Kirschner and Gerhart give several of these advances in evolutionary biology a broad public airing as coauthors of a new book, "The Plausibility of Life," published this week by Yale University Press. In it, they discuss the origins of complicated biological features-from the bat's wing to the human eye-and present their theory of "facilitated variation," which they believe addresses a major question in evolution: How can small genetic changes develop into complex, useful body parts? In a sign of the times, they also rebut claims of irreducible complexity made by Intelligent Design advocates.

    In so doing, Kirschner and Gerhart say, they are tackling an issue evolutionists have often left unexamined. "The question of how variation could be produced has been there from the beginning," says Gerhart, referring to the publication of Charles Darwin's "On the Origin of Species" in 1859. By the 1940s, the so-called "Modern Synthesis" of evolutionary theory powerfully buttressed Darwin's insights on natural selection with the post-Darwinian discoveries about the mechanisms of heredity. But, the authors write, the Modern Synthesis was "silent" about the way organisms generated variation. It is not coincidental, they add, that because "variation is the least understood of the theoretical underpinnings of evolutionary theory," it thus "is currently the favorite target" of creationists.

    Kirschner and Gerhart say this situation has now changed. Organisms, they assert, have a far greater capacity to generate rapid and complex variations than even biologists had previously supposed. Moreover, from the genetic level up to our visible features, organisms have a modular structure. In this sense, complex features are less like singularly intricate structures than a collection of building blocks.

    Significantly, Kirschner and Gerhart write, while random genetic mutations in our DNA code cause variations, these mutations do not create random effects (a traditional working assumption of many evolutionists). Instead, all organisms have maintained an essentially intact set of vital mechanisms-metabolism, reproduction of DNA, growth mechanisms, and more-for at least 2 billion years. These elements, along with a long-conserved body plan common to many animals, serve as the platform for subsequent, often more visible variations.

    Consider the elephant's trunk, the elk's antlers, and the narwhal's tusk, which all appear to be distinct, complex innovations. But as Kirschner and Gerhart point out, the same type of cell guided their growth in each animal. Moreover, the modular structure of life means these body parts could develop without affecting the rest of the organism. (A corollary is that it only takes limited genetic changes to bring about large bodily changes.) So the trunk, antlers, and tusk are really just different expressions of the same type of genetic activity-funneled through the process of natural selection, in which variations useful to a particular environment tend to survive over time.

    Kirschner and Gerhart also suggest Behe does not consider modularity in his claim that only "staggeringly complex biochemical processes" lie behind the composition of, say, an eye. As they note, the eyes of insects and mammals, each of which appear to be singularly complex, share important biochemical building blocks and connections among their components.

    "People should be asking about the nature of complexity, not just how complex it is," amplifies Kirschner, in conversation. "You look at a clock, and you see that every part is purposely made. That's what you would do if you were an Intelligent Designer. But instead, when you look at biology, you find that there are very few types of parts, and they are being co-opted from one place to another. We have a Lego-like capacity to very easily generate new structures."

    So far, "The Plausibility of Life" is receiving a warm welcome from biologists. "This is a great contribution for scientists, and I hope the general public can get a lot out of it," says Bruce Alberts, a biochemist at the University of California, San Francisco, and a former president of the National Academy of Sciences. But the authors are realistic about its immediate impact on the evolution-creation battles. "I'm not so vain as to think this book will stem the tide of the whole culture war that's going on," says Kirschner.

    Some observers are even more blunt about whether progress in biology deters evolution's opponents. "It makes virtually no difference," says Ronald Numbers, a historian of science at the University of Wisconsin, and author of "The Creationists," a history of the subject. "Creationist arguments have changed a lot, but rarely as science has gone forward."

    Nevertheless, scientists themselves insist that the kinds of insights Kirschner and Gerhart present need to be more effectively communicated. "We have failed to prepare our public to deal with challenges to the nature of science, from people who don't like our findings," says Alberts. As president of the National Academy of Sciences-his term ended in July-Alberts says he "has tried to use this, with the [Intelligent Design] movement now outraging scientists, as a teaching moment for faculty to re-think their courses....We want people to understand what science is and why [Intelligent Design] isn't science."

    Among other things, that means tackling the creationists' mantra that evolution is "only a theory," and explaining that it is based on natural principles, which can be studied and tested in labs like any other science. Granted, evolutionists must toe a fine line between emphasizing the certainties of the discipline and acknowledging areas that need more work. "Science has got to be an open process," argues Alberts, adding that if events like the Dover trial limited biologists' impulse to debate one another, it would "harm science more than the [Intelligent Design] movement itself."

    If anything, Kirschner and Gerhart hope their book will have an impact at least as substantial on their colleagues in biology. For too long, they say, researchers in its different domains-from evolutionists in the field to cell biologists in the lab-have remained isolated. "I wouldn't call it an antagonism as much as one not knowing anything about the other," Gerhart offers.

    Kirschner likes to invoke the much-quoted declaration of famed 20th-century biologist Theodesius Dobzhansky that "nothing in biology makes sense except in the light of evolution" (the title of a 1973 essay). "In fact, over the last 100 years, almost all of biology has proceeded independent of evolution, except evolutionary biology itself," Kirschner declares. "Molecular biology, biochemistry, physiology, have not taken evolution into account at all."

    As a result, scientists working on genetics, cells, and molecules-a background Kirschner and Gerhart share-have not always considered how components of an organism reveal both its physiological properties and evolutionary properties and provide a window into the history of the organism. Evolutionary science, argue Kirschner and Gerhart, will advance as more biologists place their lab research within this evolutionary framework.

    Nonetheless, many scientists think a convergence of biology's disciplines is now at hand. Whereas evolutionary biologists have famously debated whether the gene, organism, or even species is the proper unit of natural selection, current research increasingly integrates these things. "This is where it's happening," says Daniel Hartl, an evolutionary geneticist at Harvard. "Evolutionists and others in the field are not arguing about reductionism any more. What's exciting is putting it all together, from the genetic level to the organism."

    Kirschner's present domain, systems biology, is one such burgeoning research area. In it, scientists do not intensively study one part of the body at its lowest level of complexity, as in molecular biology, but rather look at the interactions of parts or functions. Even for science enthusiasts, this can seem arcane. But Kirschner is hopeful the current interdisciplinarity of biology will help the long-term public understanding of evolution.

    "I think it will affect the teaching of biology," suggests Kirschner. Comprehending the genetic basis of evolution, he thinks, will reduce the number of "just-so" stories often used in the classroom to explain adaptations, and can provide a broad set of organizing principles by which we understand animals even more diverse than the elephant, elk, and narwhal.

    "If you take all the genes of a human and look at them, most of them look just like genes in other organisms, and many of them look like genes in bacteria," explains Gerhart. Closely related species have closely matching genetic codes. But even bacteria and humans, distant relatives, share identical stretches of DNA relating to the metabolism. Such data provides powerful evidence for evolution by common descent.

    None of which, Kirschner reminds us, is to suggest that biologists have finished their work. "Scientists are in a bit of a dilemma here," Kirschner acknowledges, when it comes to making their case in the public sphere. "How do you argue that we should still study evolution if the subject is complete? I think we need to portray evolution as a tremendous and active area of investigation, where the basic principles can be well-supported. But nothing in science is ever totally complete."

    One question science cannot currently answer, Kirschner agrees, concerns the origins of life-although, unlike the Intelligent Design supporters, he considers it within the realm of scientific inquiry. This summer, Harvard announced it would fund a large-scale project on the subject, linking an interdisciplinary roster of researchers in an investigation of questions situated at the very beginning of evolution-like the development of the first cells.

    "From the single-cell bacterium to the human being, we understand evolution extraordinarily well, in many parts of it," Kirschner says. "But there are still specific issues where we have fragments of information. That's OK. We don't know everything."


    Peter Dizikes is a journalist living in Arlington. He frequently writes about science and technology.

Last modified on Monday, 21 April 2008 15:11