I have read that social Darwinism sort of underpins aspects of US culture: this came up when we studied a novel by Theodore Dreiser, who ended up on the left. The idea of competition between individuals resulting in the best coming to the top is sometimes said to be part and parcel of the 'American Dream' national mythology/philosophy. But I'm not really an American Studies person and it didn't look very dreamy as Dreiser portrayed it.