The evolution of political correctness was an exponential process going back a thousand years and more, but (as with all exponential processes) the early stages are hard to detect because the size of the phenomenon was so small.
But (like all exponential processes) once the phenomenon had became visible for sure (late 1960s), it grew very fast.
(Also the doubling-time shortened as the process advanced - so in fact it is not really exponential at all! Just figuratively.)
In this context, I think perhaps the first really evident jump into PC was the abolition movement which originated among English Quakers and spread to evangelicals, then to mass support in England.
Of course, everybody regards slavery as an evil nowadays. At least they do in a theoretical sense - although nothing is done(not even cheap and easy steps) to abolish resurgent slavery abroad; and even within the West (where slavery is tacitly tolerated by the authorities when it happens in some ethnic groups - presumably on 'multi-cultural' grounds).
Nonetheless, if you look at the abolitionist movement, it clearly has many of the characteristics of modern political correctness in embryo.
Furthermore the abolition movement was ruthless in its self-confidence, its desire to impose its reality globally: slavery was abolished everywhere in the world (except for some tiny, shrinking pockets in sub-Saharan Africa) in a long and dynamic (not to say ruthless) campaign stretching over many decades, and mostly by military coercion when the British Empire was at its height.
The passing of the acts of parliament to abolish the slave trade, then to abolish slavery in the Empire were merely the beginning of the process. The actual abolition of slavery everywhere had to be imposed by unrelenting, long-term political and military pressure, and backed-up by the guns of the Royal Navy which had a long reach.
In this respect the abolition movement was the antithesis of the feeble submissiveness of modern political correctness. Nonetheless, abolition shared the presumption of PC that ethics were susceptible of discovery and advancement - not by divine revelation, but by human social consensus.
Abolition showed that there might be an avant garde of elite opinion, and that the mass of the public might be brought around to views that they found initially incomprehesible, abhorrent or dangerous.
In particular, abolition was built on the 'discovery' (initially by Nonconformist Protestants and Anglican evangelicals) that slavery was utterly unacceptable and must be stopped at any cost was a realization that entailed overthrowing 1800 years of Christian morality.
The 'discovery' that Christianity ruled-out slavery entailed the assumption of moral progress, that modern abolitionists were more morally advanced than the ancient Greeks and Romans, than the Apostles, Saints and Holy Fathers and the greatest theologians of all previous eras.
Until the abolition movement, all societies in history had accepted slavery as a fact. Slavery was universal wherever it could be afforded.
It was only in England, among a small group of protestants in the late 1700s, that the discovery was made that slavery was intolerable, was indeed the worst of sins, and must be eradicated at any cost.
Abolition can thus be seen as an early example of progressivism - despite the contrast with PC that abolition was being advocated and implemented by muscular and militaristic Christians.
What was different about abolitionism was a fanaticism based on abstractness and universality of ethics.
Abolition was not primarily self-interested but was genuinely altruistic - in enforcing abolition upon the world the British Empire gave up a considerable amount of profitable enterprise, expended vast amounts of treasure in military action and in compensation of slave owners, expended prime manpower (and suffered heavy casualties) in the slave wars.
For instance the British military station in Sierra Leone, specifically for enforcing abolition, suffered a mortality rate of 50 percent per year due to tropical disease - a stunningly high number, such that to be stationed there was almost a death sentence - justifying its nickname of 'the white man's grave'.
And the costs were immense for many slaves, who were killed during these military actions, were slain by slavers and thrown overboard from ships to avoid incrimination, and who in many instances suffered death and extreme hardship following liberation .
So abolition has this dual face. In some ways it was the greatest altruistic moral achievement ever (in so far as costly altruism is supposedly the ultimate virtue for secular liberal morality).
In other ways abolition was the beginning of reality-proof morality, the morality of designated 'good acts' (regardless of ensuing consequences) and of the modern style prideful, hate-filled, self--gratifying justification-by-motivations - and therefore a precursor to political correctness.