Fisher's fundamental theorem of natural selection
is an idea about genetic variance in population
genetics developed by the statistician and
evolutionary biologist Ronald Fisher.
The proper way of applying the abstract mathematics
of the theorem to actual biology has been
a matter of some debate.
It states:
"The rate of increase in fitness of any organism
at any time is equal to its genetic variance
in fitness at that time."Or in more modern
terminology:
"The rate of increase in the mean fitness
of any organism at any time ascribable to
natural selection acting through changes in
gene frequencies is exactly equal to its genetic
variance in fitness at that time".
== History ==
The theorem was first formulated in Fisher's
1930 book The Genetical Theory of Natural
Selection.
Fisher likened it to the law of entropy in
physics, stating that "It is not a little
instructive that so similar a law should hold
the supreme position among the biological
sciences".
The model of Quasi-linkage equilibrium was
introduced by Motoo Kimura in 1965 as an approximation
in the case of weak selection and weak epistasis.Largely
as a result of Fisher's feud with the American
geneticist Sewall Wright about adaptive landscapes,
the theorem was widely misunderstood to mean
that the average fitness of a population would
always increase, even though models showed
this not to be the case.
In 1972, George R. Price showed that Fisher's
theorem was indeed correct (and that Fisher's
proof was also correct, given a typo or two),
but did not find it to be of great significance.
The sophistication that Price pointed out,
and that had made understanding difficult,
is that the theorem gives a formula for part
of the change in gene frequency, and not for
all of it.
This is a part that can be said to be due
to natural selection.More recent work (reviewed
by Grafen in 2003) builds on Price's understanding
in two ways.
One aims to improve the theorem by completing
it, i.e. by finding a formula for the whole
of the change in gene frequency, and accounting
for the effects of mutations.
The other argues that the partial change is
indeed of great conceptual significance, and
aims to extend similar partial change results
into more and more general population genetic
models.Due to confounding factors, tests of
the fundamental theorem are quite rare though
Bolnick in 2007 did test this effect in a
natural population
