nonDarwinian

NonDarwinian refers to evolutionary theories or explanations that do not rely predominantly on natural selection as the driver of evolutionary change. In practice, the term is used for models or observations that emphasize stochastic processes, non-genetic inheritance, or abrupt shifts rather than gradual adaptation driven by fitness differences.

Genetic drift is random change in allele frequencies from one generation to the next. It can lead to fixation or loss of alleles regardless of their effect on fitness, especially in small populations and over long time spans.

The neutral theory, proposed by Motoo Kimura, holds that most molecular variation is due to neutral mutations that spread by drift rather than by selection. The nearly neutral theory, developed by Tomoko Ohta, extends this to include mutations with very small selective effects that behave like drift.

Non-genetic or non-Darwinian inheritance includes cultural transmission in humans and other species, as well as epigenetic mechanisms that can influence phenotypes across generations without changes in DNA sequence. These mechanisms can modulate evolution and interact with selection, drift, and mutation.

Historically, proposals such as Lamarckian inheritance and, in some discussions, saltationist ideas challenged strict Darwinian gradualism. While most modern biology integrates multiple processes, some debates persist about the relative importance of selection versus drift and other factors in particular lineages or timescales.

Today, non-Darwinian aspects are considered part of a broader evolutionary framework. The modern synthesis and subsequent developments recognize that evolution results from the combined action of mutation, migration, genetic drift, and selection, with non-selective processes playing essential roles, especially at the molecular level and in small populations.