In the late 1980s, the universality of the accepted paradigm for how spontaneous gene mutations form was challenged. The paradigm of S. E. Luria and M. Delbrück (1943) described spontaneous mutation as a process akin to random thermal noise—that is, spontaneous mutation occurred before cells encounter an environment in which the mutation might prove beneficial, in a cell generation–dependent manner, and more or less randomly in the genome. This was in harmony with neo-Darwinian evolutionary thought, in which rare, randomly formed mutants gain the ability to survive by accidentally acquiring genotypes more favorable for their environment than their competitors' genotypes. In this view, the environment and its role in selection of favorable genotypes is not linked to the generation of new genotypes.