There is a paradoxical relationship between the theory of evolution by natural selection and Leftism, liberalism or political correctness.
At one level, to 'believe in' evolution by natural selection is used by the Left as a litmus test of seriousness - and 'creationism' is regarded as a marker of imbecility.
On the other hand, the Left will not accept the conclusions of natural selection when applied to humans, so that sociobiology/ evolutionary psychology is regarded with extreme suspicion (even though the discipline is colonized almost entirely by Leftists).
The politically correct Leftist ideology is primarily ethical - yet as a secular ideology it excludes divine revelation as a basis for ethics, and as a revolutionary ideology it also excludes spontaneity and common sense as a basis for ethics.
This opposition to the spontaneous and commonsensical is the basis for the aversion to natural selection - because natural selection shapes instinct.
Hence Leftism sets itself against the instinctual, has an automatic suspicion of that which is natural, because the natural is essentially 'selfish' (whether conceptualized as selfishness of organisms or of genes).
Political correctness cannot accept the implications of the natural selection it espouses, because PC regards natural selection as leading to a secular version of 'original sin' - intrinsic human selfishness.
For political correctness to accept the full implications of natural selection would therefore be to refute itself.
It would be for PC endorse selfishness, since animals are selfish; it would be to endorse cruelty, because animals inflict suffering on each other.
Political correctness (correctly!) recognizes that natural selection cannot lead to real virtue, to real disinterested unselfishness - therefore PC is intrinsically trying to get outside natural selection.
Political correctness, as the most advanced form of Leftism, has evolved to locate virtue in terms of abstract ethical rules which are instantiated outside of the human organism and human society.
(Given the suspicion of the spontaneous and commonsensical) these abstract ethical rules ought to be followed literally even when (especially when) they contravene instinct and common sense.
Therefore, for political correctness, the ideal is that all human behavior should be regulated by abstract ethical rules - and the outraging of spontaneous human morality is a feature, not a bug: it is evidence of transcending the 'natural' (where the natural is intrinsically regarded as corrupt).
But which rules?
If they are not to be purely arbitrary, abstract ethical rules must have two characteristics:
1. Moral inversion.
PC rules must contradict spontaneous common sense.
2. Face plausibility.
Since there are (in principle) an 'infinite' number of morally-inverted ethical rules; those which are selected must have a kind of face plausibility - must have (in the social context of modern society) a kind of platitudinous uncontradictability; for instance when denial of the morally-inverted rule must seem to convict the contradicter of cruelty and/ or selfishness.
This means that the ethical principles of political correctness depend on an implicit consent; they cannot be founded, nor defended in any fundamental fashion, but only by 'sophistry', displacement and counter-attack.
They are not necessary, but neither are they arbitrary. They are not approximate, neither are they exact - yet their interpretation must be precise and literalistic.
(Specific PC rules, developed in this fashion, are then subjected to progressive harmonization/ simplification by being brought under ever-more-general 'meta-principles'- such as diversity, equality, peace, non-discrimination. Presumably these meta-principles will - if PC lasts long enough - eventually be brought together under a single primary, foundational evaluation.)
Literal interpretation of rules in the face of the natural means that there is no such thing as moderation in PC, nor is there any hierarchy of PC transgressions: use of a single taboo word in a private conversation may elicit the full majesty of legal prosecution, social exile, permitted violence; yet tyranny, torture, rape and murder may be ignored when to notice these might be seen to tend towards disruption of over-arching PC priorities.
The two options are full and unrelenting legalism, or complete ignoring: the end goal of promoting universal PC justifying the means of ignoring specific transgressions of PC.
Natural selection is seen as having led to that to which political correctness is opposed: the natural and instinctive.
Hence PC opposes the consequences of natural selection, even as it accepts (as dogma) the reality of natural selection.
The rules of PC are therefore set-up in opposition to natural selection as abstract and partial summaries of concrete and infinitely complex realities - presented as self-evidently true - followed and enforced without compromise in the face of spontaneity and common sense - and the denial of which is seen as a moral monstrosity.