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Equation 2 · Part 4 · From Origins to Frontier: A History of Evolutionary Biology and Ecology

=

Var⁡(Δp)=p(1−p)2Ne,\operatorname{Var}(\Delta p) = \frac{p(1-p)}{2N_e},
=

What this part means

The expressions on both sides represent the same quantity under the stated assumptions.

Its job in the formula

The equals sign connects the complete expression on the left with the complete expression on the right. Both sides must have compatible units.

The passage around this formula

Sewall Wright’s 1931 paper, “Evolution in Mendelian Populations,” added the piece Fisher’s and Haldane’s more deterministic treatments lacked: a formal account of genetic drift, the random change in allele frequency from generation to generation caused by finite population size [ 3 ] . Wright showed that in a randomly mating population of effective size NeN_e , the variance in allele frequency change per generation from sampling alone is Var⁡(Δp)=p(1−p)2Ne\operatorname{Var}(\Delta p) = \frac{p(1-p)}{2N_e}. for a diploid population starting at allele frequency p . This single expression carries a real consequence: small populations can fix or lose alleles by chance alone, independent of whether those alleles are beneficial, neutral, or mildly…

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Learn the underlying idea

An equals sign says that the expression on its left and the expression on its right have the same value under the stated definitions and assumptions.

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Sources cited in the surrounding passage

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