Summary
Proposes that most molecular variation results from drift of selectively neutral mutations rather than selection.
In depth
Motoo Kimura argued that most fixed molecular differences are neutral, with drift determining their fate. It does not deny selection on phenotype but changed how molecular evolution is viewed and gave a null model.
Neutral changes accumulate at a rate equal to the mutation rate, which underlies the molecular clock.
Kimura's theory (1968), with King and Jukes' similar proposal, was based on high levels of protein variation and a roughly constant rate of substitution. The rate of neutral substitution equals the mutation rate, independent of population size, which underpins the molecular clock. Tomoko Ohta's nearly neutral theory adds slightly deleterious mutations whose fate depends on population size.
Tests use the McDonald-Kreitman test, comparing polymorphism with divergence at synonymous and non-synonymous sites, and dN/dS ratios: a value near 1 means neutral, below 1 purifying selection, above 1 positive selection. The theory provides the null model for detecting selection in genomes.
Frequently asked questions
What is Neutral Theory?
Proposes that most molecular variation results from drift of selectively neutral mutations rather than selection.
Which area of biology covers Neutral Theory, and how advanced is it?
Neutral Theory is one of the 53 topics in Evolution. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Molecular Clock, Evolution, Convergent Evolution.
Why does Neutral Theory matter?
It shows that much of molecular change is not adaptive, but drift.
Can you give an example of Neutral Theory?
Synonymous sites evolve faster than nonsynonymous sites since they are under less constraint.
What should I learn before Neutral Theory?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Neutral Theory. Advanced topics assume the Intermediate vocabulary.
What topics are related to Neutral Theory?
The closest topics to Neutral Theory are Molecular Clock, Evolution, Convergent Evolution, Punctuated Equilibrium. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Neutral Theory?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Neutral Theory. To practise the whole of Evolution, use the Evolution quiz.
How is Neutral Theory different from Molecular Clock?
Neutral Theory: Proposes that most molecular variation results from drift of selectively neutral mutations rather than selection. Molecular Clock: Uses the steady rate of neutral mutations to estimate when lineages diverged. Read both side by side and note what each one explains.
How should I study Neutral Theory step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Molecular Clock and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.