The theory of evolution when interpreted into Social Darwinism in the 19th-20th centuries did NOT "make men equal" - quite the opposite. It suggested that those men with the greatest gifts and powers would out-strip the weaker, and that this was decreed by Nature. Social Darwinism suggests that inequality is part of Nature; it is the God of Christians who says that all men are equal under God.
Pagans are never "under" the yoke of "god".

Not Darwin or anyone else "plunges" us into Nihilism; Nihilism is the LOGICAL OUTCOME of Christian ideals, most particularly the belief in an Absolute Truth.