Brief Excerpts*
From Coevolution: Genes, Culture, and Human Diversity by William H. Durham.
On “What are the sources of variation?” leaving out secondary variation sources.
“In the case of organic evolution, two different kinds of processes have been identified as ‘primary,’ or initial, sources of variation: mutation, or the spontaneous introduction of variation at the level of genotypes and individuals; and speciation, the formation of variable, noninterbreeding descendant populations.”
On “What are the mechanisms of transmission?”
“In the case of organic evolution, the answer to this ‘transmission question’ has long been supplied through reference to Gregor Mendel’s laws of inheritance, that is, through reference to the regularities of gene transmission caused by actual biological reproduction. Today […] there is increasing evidence for irregularities or ‘violations’ of Mendel’s laws, and for non-Mendelian processes of gene duplication and transmission within and between species. […] these findings now force us to reconsider what were earlier points of difference between genetic and cultural transmission, such as the assertion of the anthropologist Alfred Kroeber that whereas organic evolution ‘really does nothing but diverge,’ culture ‘diverges, but syncretizes and anastomoses, too,’ as a consequence of interpopulational diffusion and borrowing. […] there would seem to be possiblities for coalescenceand assimilation in the transmission processes of both systems.”
On “What are the main causes of transformation?”
“Darwin avoided ‘Wallace’s fatal flaw’ of hyperselectionism. […]
[He] also recognized that natural selection commonly acts through individual-level differences. Whatever the reasons for parent-child differences, he argued, it was ‘the steady accumulation, through natural selection, of such differences, when beneficial to the individual, that [gave] rise to all the more important modifications of structure.’ […] if natural selection general favored ‘slight variations, each good for the individual possessor, there were direct implications for the pattern of change in organic evolution, or what are now called the tempo and mode of transformation. Here, too, Darwin was explicit: ‘That natural selection will always act with extreme slowness I fully admit. [sic] As natural selection acts solely by accumulating slight, successive favorable variations, it can produce no great or sudden modification; it can act only by very short and slow steps. Hence the canon of ‘Natura non facit saltum’ [nature does not make great leaps].’
[…] Darwin was the first to admit his predominant Power ‘must be slow and gradual’ in operation, a view that is today called ’phyletic gradualism,’ and he was the first to defend this position with reference to geological record.”
*(because to simply quote would be too much)
