Beginning in the 1960s, molecular
considerations contributed to a powerful new critique of Darwinism.
Advocating what was called, variously, "non-Darwinian
evolution," and later the "neutral theory,"
Motoo Kimura, Tomoko
Ohta, Jack King and Thomas
Jukes argued that the majority of mutants at the molecular
level were selectively insignificant or "neutral"
(or at least "nearly neutral"). Thus, evolution
at the molecular level was largely a matter of random genetic
Some critics of the neutral theory conceded that evolution at the molecular level might be mainly a matter of the drift, but maintained that evolution at the phenotypic level was mainly due to natural selection. Other critics refused to concede even the molecular level to the neutralists. The ensuing neutralist-selectionist debates have had broad conceptual and methodological ramifications throughout evolutionary biology.