When John Millington Synge was 14, he got hold of a copy of Charles Darwin’s On the Origin of the Species. He opened it at random on a passage in which Darwin points up the similarity between a human hand and the wing of a bird or bat, and asks how this can be explained other than through evolution. Having already developed a keen interest in natural science, Synge recognised the overwhelming force of Darwin’s argument. He also recognised the implications of that argument for the Protestant faith in which he had a deep and implicit belief.

As he read Darwin’s words, Synge flung the book aside and rushed out of the house. “The sky seemed to have lost its blue and the grass its green. I lay down and writhed in an agony of doubt. My studies showed me the force of what I read, and the more I put it from me, the more it rushed back with new instances and power.”

He lay on the ground a long time, then went back into the house, got the book and hid it outdoors. But what had been read could not be unread. A crucial step had been taken towards the creation of Ireland’s greatest playwright.

In James Joyce’s A Portrait of the Artist, Stephen Daedalus opposes his own neo-Thomist views on beauty to the “drearier” notions of sexual selection proposed by Darwin. In Ulysses, Darwin is mocked. There is some speculation that the unprepossessing Costello is “the missing link of creation’s chain desiderated by the late ingenious Mr. Darwin”.

Cited as tongue-in-cheek proof of Leopold Bloom’s youthful rectitude is the fact that, during “nocturnal perambulations”, he had “advocated ... the revolutionary theories of Charles Darwin”.

Joyce’s writing, with its attempt to control the randonness of evolution within an aesthetic framework, is typical of the deep strain of Irish literature dedicated to opposing the shaping power of the imagination to Darwin’s terrifying emphasis on accident.

Bernard Shaw remained a steadfast critic of natural selection, preferring to elieve in a bigger “life force”. Yeats believed that “our instinct repudiates Darwin’s exaltation of accidental variations” and dedicated himself to the discovery of mystical patterns in everything.

The only major Irish writer who could be said to accept a Darwinian world is Samuel Beckett, whose universe is shape by the extinction of species, including man. Beckett bought On the Origin of the Species in 1932 and dismissed it, in an odd but clearly uncomplimentary phrases, as “badly written cats-lap.”

Yet one image from the book - Darwin’s parable on instinct, using the example of a caterpillar working on its hammock, recurs again and again, in Echo’s Bones, Murphy and Watt. And the grim humour of Endgame is steeped in Darwinian dystopia. When Clov discovers a louse in his trousers, Hamm urges him to kill it because “humanity might start from there all over again!”

Yet, as well as these negative or fearful reactions to Darwin, there is another immense impact of his work. As Synge so vividly recalled, On the Origin of Species delivered a sickening blow to the religious faith of a generation. This was particularly true of the generation of Protestant writers who created the Irish Literary Movement.

The loss of faith triggered by Darwin was, in the Irish context, as much political as religious. Protestantism was a political identity, almost inextricable from Unionism. What happens when that Protestantism is destroyed, and a whole package of ethnic allegiances is thereby undermined? A new identity has to be invented. In the course of doing so, the young writers invented a new Ireland.

Synge recalled the process of alienation that followed his reading of Darwin as a “terrible experience”. Becoming an atheist cut him off from history, family and community: “By it, I laid a chasm between my present and my past and between myself and my kindred and friends.” His only release lay in art (music and poetry) and in nature. And, eventually, in Ireland.

“Soon after I relinquished the Kingdom of God,” Synge recalled, “I began to take a real interest in the kingdom of Ireland. My politics went round from a vigorous and unreasoning loyalty to a temperate Nationalism. Everything Irish became sacred ...” From that flowed Synge’s wanderings in Wicklow and Kerry, his stays on the Aran Islands, and his great plays. By stealing his inherited certainties, Darwin pushed him, and subsequently much of Irish 20th century culture, into a whole new imaginative space.