Meanings of undirected variability in English

Second, he recognizes that Darwin's system entails a crucial assumption of isotropic, undirected variability.

Eimer understood the crucial role of undirected variability in the logic of Darwinian argument.

141-146): Lamarckism and orthogenesis deny the principle of undirected variability; saltationism refutes the claim that variation must be small in extent.