Many northern Europeans regressed from believing in Adam and Eve to believing in stuff much closer to tribal (as opposed to human) ancestral stories.
In an excerpt from Extreme North: A Cultural History, Bernd Brunner, a writer on culture, explains:
Based on the wealth of new knowledge, the idea of a long Germanic prehistory seemed worthy of closer examination. And regardless of whether the origins of the northern cultures were attributed to the North itself or to India or Persia, many researchers now considered belief in the biblical story of creation—scorned by some as “Jewish fables”—to be out of date. No one could imagine what the consequences this shift in thinking would have.
The idea that White people originated in the Caucasus, which in the nineteenth century was closely entwined with the question of the genesis of the Germanic peoples, was first formulated by Johann Friedrich Blumenbach. In 1776, he used the term Caucasian to refer to those peoples who were “predominantly white in color” and, in his eyes, most beautiful. Later the writer Joseph Görres also traced the historical roots of the European peoples to the Caucasus. In his 1807 essay “Religion in History,” he wrote: “All that is powerfully, ruggedly and jauntily heroic invariably had its epicenter in [the Caucasus]; all great conquerors and all world-commanding characters have poured down from its heights like wild mountain streams, and the earth’s other mountains willingly acknowledged this range as their king. Just as in later ages the Celtic and Germanic myths and those of the northern Scandinavians that all spring from the genuine heroic spirit began there.”
Bernd Brunner, “How the theory of evolution sparked bizarre ideas about human origins in the North” at Big Think (February 17, 2022)
Many cultures have traditions according to which (quelle surprise!) in-group members are superior to out-group members. A common ancestral pair implicitly undermines such view, with predictable consequences. Getting rid of Adam and Eve was bound to bring older, more questionable traditions to the fore.
You may also wish to read: Politics has invaded the world of human fossil analysis At Areo: “Perhaps the most well-known example of the politicization of ancient DNA studies is the long legal battle for control of the remains of Kennewick Man, which were found in Washington State in 1996. Based on skull shape—the best evidence available at the time—scientists initially inferred that his most probable ancestry was European. Local Native American groups sued to have his remains reburied without further analysis under a 1990 US federal law…”