"Evolutionary Theory’s Welcome Crisis" by John Dupre | Project Syndicate

"Evolutionary Theory’s Welcome Crisis" by John Dupre | Project Syndicate

For the last 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.

Other assumptions, however, 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. But examination of genomes – particularly microbes – has shown that genes moving between distantly related organisms are an important catalyst of evolutionary change.

Moreover, the new synthesis assumes that the main drivers of evolution are small mutations generated by chance within a species. But 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 multicellular animals) – can generate large and crucial evolutionary change.

This can create chaotic effects rather than just randomness being behind mutations. For example one mutation might build on another as dependent variables to amplify the effects. For example a mutation might cause R prey to have larger lung, a later mutation to longer legs might then be amplified because the animal already has an extra ability to supply oxygen in this faster running. 

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.