Shiny! Permission to steal? (with attribution, of course)
This is excellent. Thanks.
True, but it was the increasingly available sequence data that “sealed” the deal. Its pretty obvious when you read Kimura’s 1991 paper (which you probably did decades before I was born).
Major slip. Please ignore.
Its not about Darwinian evolution (variation plus natural selection strictly), but Darwinism (variation plus natural selection almost all the time).
Help yourself!
Already a question from FB: Where does horizontal gene transfer fit into this diagram? (genomics??)
I’m just pointing out that the debate between neutralists and selectionists goes back way beyond Kimura. Genetic diversity, of any sort, within populations has long been an argument for neutralism.
I know and all I am saying is that the belief that natural selection is mostly responsible for all evolutionary change is no longer tenable. Selection, drift and biased gene conversion are the drivers of evolutionary change.
I thought selectionists tried to account for existing genetic diversity by appealing to balancing selection prior to the 1960s?
I should explicitly include that! Gonna need a bigger boat, er, purple circle.
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I have a request to reuse from another teacher on FB, which I said would be OK. Maybe we need to do a little more to cite your work properly though. Do you have a web page I can give them?
I don’t have it anywhere specific - I have it in a powerpoint, and uploaded it as a picture onto imgur. So it can be credited to me - Dan Stern Cardinale - adapted from Noble, 2015, specifically figure 1. I should put “niche construction” back in, though, along with horizontal gene transfer, and maybe symbiogenesis. Bah, time to update my figure.
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Possibly, but that would be an ad hoc response to the discovery of an unexpected amount of genetic diversity.
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Just to try to clarify the history a little: John Harshman is right that neutral genetic change was invoked well before Kimura, mostly by systematists. (Though Sewall Wright did so too around 1930, as Will Provine documented in his biography of Wright). But in the 1950s population geneticists became increasingly aware of the power of natural selection, that to be neutral in a population of size 1 million, a genotype would have to have a selection coefficient of less than 1 in a million, at least.
In the 1950s population geneticists were divided between agreeing with H.J. Muller that we would expect most variation to be rare alleles maintained by mutation in the face of “purifying selection”, and agreeing with Theodosius Dobzhansky that variation was likely to be common and maintained by “some form of balancing selection”. Neither had much empirical evidence at the gene level. Keep in mind that the genetic code was not finally worked out until 1963, and before that only a few molecular biologists appreciated that there would be redundancy in the code. It was known that there was too much DNA. Population geneticists tended to assume that if junk DNA came into the genome, it would quickly be cleared out by selection as being somewhat deleterious. (I, a student after 1960, thought that way too).
Crow and Kimura in 1964 calculated the expected standing variation from neutral mutation, but mostly as a null case in an exploration of the effect of drift on Dobzhansky’s scenario. The first real statement of the possibility of neutral mutation as an explanation for variation at the gene level was by Richard Lewontin in his 1966 Genetics paper with Jack Hubby. He gave it as one of the possible explanations for the high amount of electrophoretic variation they found, but he did not commit to that explanation.
“Junk DNA” was put on the agenda by Susumu Ohno in 1969 and thereafter population geneticists began to appreciate that a lot of it could arise and it would be cleaned out rather slowly and weakly. Creationists are entirely wrong when they assert that Junk DNA was needed by evolutionary biologists and thus assumed. Most resisted it for a while.
As to what names should be given to evolutionary biology theories in different periods, there is no real consensus on that. But to explain phenotypic adaptation, pure neutrality is mostly not credible.
Sorry to go on so long, but my career has too, so I have a perspective that is long, so perhaps this may be helpful.
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