Pronunciation: (ôr"thu-jen'u-sis),[key] —n. 1. Biol. a. Also called orthoselection. evolution of a species proceeding by continuous structural changes in a single lineage without presenting a branching pattern of descent.
b. a theory that the evolution of a species in a continuous, nonbranching manner is due to a predetermined series of alterations intrinsic to the species and not subject to natural selection.
2. Sociol.a hypothetical parallelism between the stages through which every culture necessarily passes, in spite of secondary conditioning factors.