Wed, Sep 12, 2012 - Page 9 News List

Science welcomes an evolutionary theory that is itself evolving

By John Dupre

Those who believe that a supernatural being created the universe have never posed an intellectual challenge to evolutionary theory. However, creationists, whether biblical fundamentalists or believers in “intelligent design,” do pose a threat to scientific thinking. Indeed, creationism’s insidious genius lies in its ability to reinvent evolution in its own image as a dogmatic belief system — and thus the antithesis of science.

The creationists are right about one thing: Contrary to the impression given by much popular writing on the subject, the theory of evolution is in crisis. However, this is a positive development, because it reflects the non-linear progress of scientific knowledge, characterized by what Thomas Kuhn described in his influential book The Structure of Scientific Revolutions as “paradigm shifts.”

For the past 70 years, the dominant paradigm in evolutionary science has been the so-called “new synthesis.” Widely publicized in recent years by Oxford evolutionary biologist Richard Dawkins, the new synthesis unites Darwin’s theory of natural selection with Mendelian genetics, which explains heredity.

The current crisis in evolutionary science does not imply complete rejection of this paradigm. Rather, it entails a major, progressive reorganization of existing knowledge, without undermining the fundamental tenets of evolutionary theory: Organisms alive today developed from significantly different organisms in the distant past; dissimilar organisms may share common ancestors; and natural selection has played a crucial role in this process.

However, other assumptions are under threat. For example, in the traditional “tree of life” representation of evolution, the branches always move apart, never merging, implying that species’ ancestry follows a linear path and that all evolutionary changes along this path occur within the lineage being traced. However, examination of genomes — particularly microbes — has shown that genes moving between distantly related organisms are an important catalyst for evolutionary change.

Moreover, the new synthesis assumes that the main drivers of evolution are small mutations generated by chance within a species. Recent evidence suggests that large changes, caused by the absorption of a chunk of alien genetic material, may be just as significant. Indeed, the absorption of entire organisms — such as the two bacteria that formed the first eukaryotic cell (the more complex cell type found in multi-cellular animals) — can generate large and crucial evolutionary change.

Further destabilizing evolutionary theory is the growing realization that many factors, not just the genome, determine an individual organism’s development. Ironically, as the discovery of DNA’s structure — initially lauded as the final act in the triumph of the new synthesis — led to a better understanding of genomes’ functioning, it ended up weakening belief in their unique role in directing biological development. Those who long deplored the omission of development from evolutionary models — a decades-old critique made under the scientific banner of evolutionary developmental biology (“evo-devo”) — together with the insistence that organisms’ development draws on a wide variety of resources, have been vindicated.

Recent developments in molecular biology have put the final nail in the coffin of traditional genetic determinism. For example, epigenetics — the study of heritable modifications of the genome that do not involve alterations to the genetic code — is on the rise. And the many kinds of small RNA molecules are increasingly recognized as forming a regulatory layer above the genome.

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