Haldane 1937

Citation

Haldane, J. B. S. (1937). The effect of variation of fitness. The American Naturalist, 71(735), 337-349.

Links

• https://www.journals.uchicago.edu/doi/abs/10.1086/280722
• https://www.jstor.org/stable/2457289
• http://hawaiireedlab.com/pdf/haldane1937.pdf (internal lab link only)

Notes

Paragraph One

Haldane points out the distinction between Darwinian evolution (novel adaptation) and stabilizing selection (or purifying selection or "maintenance" selection) that removes mutations which result in a phenotypic change.

Paragraph Two

The change in frequency of alleles resulting in novel adaptation can be very slow in human terms; however, extremely fast on a geologic timescale. Very small fitness differences in numbers of offspring could be virtually impossible to detect by direct observation yet have a very real evolutionary effect.

"In order that an observed viability difference of 0.1 per cent. should exceed twice its standard error, we should have to observe at least sixteen million individuals." If the average number of offspring per individual is two, for a population at constant size, this is expected to be Poisson distributed with a variance (σ²) of two.

Standard Error = [math]\frac{\sigma}{\sqrt{n}} = \frac{\sqrt{2}}{\sqrt{8,000,000}} = 0.0005 = 0.001/2[/math]

It is implied that two samples of size n=8,000,000, half with the genotype and half without, would be compared for a total of 16 million.

Paragraph Three

Again, adaptive evolution is expected to be very slow and not observable on a time-scale of human lifetimes (however, today we know of exceptions to this where observable evolution can happen quite rapidly). Except, Haldane says, possibly in cases of adapting to changes in the environment many of which are human caused, "agriculture, fishing and industry". "The balance of nature has recently been upset in a manner probably without precedent in our planet's history; and hence on the Darwinian theory we should expect that evolution was proceeding with extreme and abnormal speed."

Paragraph Four

The observation is made that in spite of selection against less fit (mutant) individuals in a species, and that this reduction in fitness is heritable, these individuals continue to appear at a roughly constant frequency over time, implying a deleterious-mutation-purifying-selection equilibrium.

Paragraph Five

Two different ways of thinking about fitness are defined, within a generation and over time. To be continued ...

Terms

Facies - appearance. https://en.wiktionary.org/wiki/facies