A theory that variations in evolution follow a particular direction and are not merely sporadic and fortuitous.
- ‘Mutation bias is not enough to produce orthogenesis, however.’
- ‘The data is inconsistent with orthogenesis, and somehow thinks that because he can draw a line from an extant animal to its many-times-great grandparents, he has supported directed evolution.’
- ‘Weidenreich tried to explain the seeming contradiction between isolated regional development and the unity of the human species by advancing the notion of orthogenesis, or directed evolution.’
- ‘A once-popular hypothesized evolutionary mechanism was orthogenesis, in which change in organisms was due not to natural selection, but to internal directional trends within a lineage.’
- ‘In contrast, other scientists imagine channeling, aka orthogenesis, to exist not only for individuals but also for species and for evolution: while there are lots of possibilities, the domain is restricted.’