Fisher's Theorem

A population-genetic theorem linking the selection component of fitness change with additive genetic variance in fitness.

Fisher’s fundamental theorem concerns the component of change in mean fitness attributable to natural selection, expressed in terms of additive genetic variance in fitness under the theorem’s definitions. This is a carefully defined biological result, not an equation equating every kind of diversity with faster improvement.

Total change also involves changes in the environment and other components outside that partial selection calculation. Mean fitness need not rise continually. For practical analogies, the useful questions concern heritable or reproducible variation, differential success, and what gets retained. Team diversity, portfolio diversification, and organizational adaptability require their own mechanisms and evidence; Fisher’s theorem does not prove their benefits.

When to use it

Useful for understanding evolutionary theory and scrutinizing analogies about variation and adaptation.

How it can help

Check the kind of variation and distinguish a partial selection effect from total observed change.