In the early twentieth century, evolutionary biologists argued whether there was enough genetic variation in populations to explain the diversity of life by natural selection
With the advent of protein electrophoresis and DNA-level analysis, the problem turned on its head: the neutralist school arose from the idea that there was too much genetic variation to be maintained by natural selection. What are some of the arguments and observations neutralists cited to support the idea that much variation is neither favored nor disfavored by natural selection?
More genetic variation is expected in noncoding regions, such as intergenic areas and introns, and has indeed been found to be the case. Also, owing to redundancy in the genetic code, the third codon position can often be variable and still specify the same amino acid. More variation might therefore be expected at third base-pair positions in codons, which has also been found to be the case.
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Fill in the blank(s) with the appropriate word(s).
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