I continue to puzzle over the way that the Left has embraced 'macro'-selection (the origin of species, of form) as a metaphysical dogma applying to humans - while suppressing discussion of micro-selection (adaptation, the shaping of form) as it applies to humans.
Such that to doubt that species evolved - and especially to doubt that humans evolved - is regarded as an extreme form of intellectual stupidity; while to assert the observable fact that humans that have adapted to (been selected by) their conditions over the past dozens of generations, is a discourse policed with extreme strictness among the elites.
So, what was natural selection for? What was the point of believing it? In the years after NS was brought into prominence by Darwin, what work did the concept do?
There was, of course, the anti-Christian aspect. And this was perhaps the main value of macro-evolution in general discourse - to explain the origins of the human species without reference to divine intervention.
Because, let's be quite honest, biological taxonomy, the classification of living things, is a highly technical minority business; and while it is vital to the science is not and seldom has been exactly a hot topic either within biology or in public discourse - except insofar as it applies to humans...
(Indeed, the concept of natural selection didn't actually make all that much difference to the classification of living things, just tinkering at the edges: most of taxonomy had already been done by 1859.)
So, to simplify, the main function of macro-evolution in general intellectual discourse was to create a metaphysical framework that assumed humans had evolved - the specific details of which were unimportant, since they have been and continue to be constantly changed.
But what of micro-evolution?
Well, in the 19th century this was mainly applied to human society, in 'Social Darwinism' - that was surely the main positive interest of the theory of natural selection.
The interest was a matter of how natural selection could explain differences between races, between men and women, and human society at different stages of civilization - in sum, how natural selection could explain the specifics of human behavior.
These was among the themes of The Descent of Man - Darwin's follow-up to The Origin of Species. Unsurprisingly, Descent (including its path-breaking descriptions of sexual selection) was pretty much forgotten for many decades and remains one of Darwin's least known writings.
The Leftist Western intellectual elites were happy with the atheistic metaphysics of natural selection, but very worried by the use of natural selection to explain human behavior in terms of adaptation; and for many decades (since the ascendancy of the Left among elites in the 1960s) this discourse has been policed with extreme strictness.
Indeed, the whole domain of differences between humans became a taboo subject - never to be discussed freely and candidly.
When sociobiology emerged, it was attacked with extreme aggression: deploying the crudest mob intimidation. Only when 'evolutionary psychology' emerged with a dogma against all significant human evolution since the evolution of 'anatomically modern' Homo sapiens some 150,000 years ago was pressure relented somewhat.
This dogma of the essential unity of mankind was, in fact, another re-assertion of macro- over micro-evolution - since it meant that significant adaptation was only of the species, and not within the species - yet even here the discussion of male female differences was fraught with hazard.
So that is my current answer to the question of what work does natural selection do in public discourse: macro-evolution (speciation) frames the question of human origins and purpose such as to exclude divine causes; micro-evolution (adaptation) provides explanations for observable differences between humans.
Macro-evolution is almost wholly a framing structure for science - and there is no direct human knowledge or experience to support it; while micro-evolution is a matter of direct observation in terms of, for example, the spontaneously obvious workings of heredity among individuals and groups and the perceptible effects of population changes (demographics).
Macro-evolution is therefore essentially metaphysical - and Leftist (since the framework is intrinsically atheist - excludes god/s); while micro-evolution is essentially scientific and threatening to Leftism (since it challenges intrinsic Leftist dogmas about equality and the causes of difference).
So, back in the nineteenth century macro-evolution was used in public discourse to support atheism, while micro-evolution was used to support Social Darwinism.
Therefore, presumably the reason that (contrary to common sense and experiential support) the first has become a dogma while the second has become a taboo is that twenty-first century politics is pro-atheist but anti-Social Darwinist.
Note: For previous postings on this subject, search this blog for "selection"