But it’s not about whether there’s a major crisis with evolutionary theory.
It’s about the mechanisms responsible for evolution, and why Darwin’s contribution–natural selection– is not the only one, contrary to many popular accounts.
At Pharyngula, PZ Myers elaborates:
I was rather surprised yesterday to see so much negative reaction to my statement that there’s more to evolution than selection, and that random, not selective, changes dominate our history. It was in the context of what should be taught in our public schools, and I almost bought the line that we can only teach a simplified version of evolution in grade school, but then it sunk in that I was talking to a group of adults about the standard biological perspective, and their reactions were a mix of total bafflement, indignant rejection, and strange evasive waffling. Well, when should we talk about this stuff, then? Do I have to start making day trips to the local nursing home? Or maybe we should be honest from the very beginning about the complexity of modern evolutionary theory and how it has grown to be very different from what Darwin knew.
Darwin’s key contribution was natural selection. But the wide world of genetics was still in the future. And it’s turned out to make a huge difference to the progress of the theory.
First thing you have to know: the revolution is over. Neutral and nearly neutral theory won. The neutral theory states that most of the variation found in evolutionary lineages is a product of random genetic drift. Nearly neutral theory is an expansion of that idea that basically says that even slightly advantageous or deleterious mutations will escape selection — they’ll be overwhelmed by effects dependent on population size. This does not in any way imply that selection is unimportant, but only that most molecular differences will not be a product of adaptive, selective changes.
Larry Moran at Sandwalk adds his two cents:
What Neutral Theory tells us is that a huge number of mutations are neutral and there are far more neutral mutations fixed by random genetic drift (than) there are beneficial mutations fixed by natural selection. The conclusion is inescapable. Random genetic drift is, by far, the dominant mechanism of evolution.
Many people seem to equate Neutral Theory with random genetic drift. They think that random genetic drift is only important when the alleles are neutral (or nearly neutral). Then they use this false equivalency as a way of dismissing random genetic drift because it only deals with “background noise” while natural selection is the mechanism for all the interesting parts of evolution. I think we should work toward correcting this idea by separating the mechanisms of evolution (natural selection, random genetic drift, and others) from the quality of alleles being produced by mutation (beneficial, detrimental, neutral).
Neither of these academics are outliers in evolutionary biology. But there are popularizers of Darwinian evolution, Richard Dawkins and Daniel C. Dennett come to mind, for example, who might be loath to endorse the idea that natural selection is not the principal driving force of evolution.
Without getting into a detailed account of drift or neutral theory, suffice it to say that biologists can get into real food fights about the extent to which both genetic drift and neutral (and nearly neutral) theory influence the evolution of new species.
Eugene V. Koonin’s 2011 book The Logic of Chance, is an excellent overview of what the status of evolutionary theory is amongst the specialists.
Koonin runs the Evolutionary Genomics Research Group at National Center for Biotechnology Information. In the preface, he writes:
The most straightforward incentive to write about the emerging new vision of evolution is the genomic revolution that started in the last decade of the twentieth century and continues to unfold. The opportunity to compare the complete genome sequences of thousands of organisms from all walks of life has qualitatively changed the landscape of evolutionary biology. Our inferences about extinct, ancestral life forms are not anymore the wild guesses they used to be (at least, for organisms with no fossil record). On the contrary, comparing genomes reveals numerous genes that are conserved in major groups of living beings (in some cases, even in all or most of them) and thus gives us a previously unimaginable wealth of information and confidence about the ancestral forms. For example, it is not much of an exaggeration to claim that we have an excellent idea of the core genetic makeup of the last common ancestor of all bacteria that probably lived more than 3.5 billion years ago. (Kindle Locations 69-75).
One of the casualties of the genomic revolution is the concept of the Tree of Life, one of the key metaphors of biology since Darwin. And whether the Tree can or should be salvaged, according to Koonin, remains a matter of serious debate.
At the distinct risk of earning the ire of many for associating with a much-maligned cultural thread, I call this major change the transition to a postmodern view of life. Essentially, this signifies the plurality of pattern and process in evolution; the central role of contingency in the evolution of life forms (“evolution as tinkering”); and, more specifically, the demise of (pan)adaptationism as the paradigm of evolutionary biology. Our unfaltering admiration for Darwin notwithstanding, we must relegate the Victorian worldview (including its refurbished versions that flourished in the twentieth century) to the venerable museum halls where it belongs, and explore the consequences of the paradigm shift.
The Nye/Ham debate was fun. But perhaps it’s time for a Dawkins/Koonin debate.