orthogenetic

Orthogenetic refers to a concept in evolutionary biology that proposes evolution proceeds in a predetermined, directional manner. This view suggests that organisms evolve along a specific path towards increasing complexity or perfection, often driven by inherent internal forces rather than solely by environmental pressures. The term "orthogenesis" itself comes from the Greek words "orthos" meaning straight or correct, and "genesis" meaning origin or creation.

This idea was more prevalent in the late 19th and early 20th centuries. Proponents of orthogenesis often pointed to apparent linear trends in the fossil record as evidence for this directed evolution. For example, the gradual increase in the size of horses over geological time was sometimes cited. However, modern evolutionary theory, largely based on Darwinian natural selection and genetic drift, does not support the idea of a predetermined or directed path for evolution. While evolutionary lineages can show trends, these are generally understood as responses to environmental factors and contingent on genetic variation, not as inherent directional forces. The concept of orthogenesis is now largely considered a historical idea in evolutionary thought, superseded by more comprehensive explanations.