Haldane's dilemma

Haldane's dilemma is a limit on the speed of beneficial evolution, calculated by J. B. S. Haldane in 1957. Motoo Kimura's landmark paper on neutral theory in 1968 built on Haldane's work to suggest that most molecular evolution across species is neutral, framing this is as a resolution to the dilemma. However, adaptive evolution might explain a significant fraction of substitutions in protein coding sequence. Other solutions have since been proposed.

Presentation by Haldane

Substitution cost

In the introduction to The Cost of Natural Selection Haldane writes that it is difficult for breeders to simultaneously select all the desired qualities, partly because the required genes may not be found together in the stock; but, he writes,

especially in slowly breeding animals such as cattle, one cannot cull even half the females, even though only one in a hundred of them combines the various qualities desired.

That is, the problem for the cattle breeder is that breeding only from the specimens with the desired qualities will yield too few individuals in the next generation. Haldane states that this same problem arises with respect to natural selection. The problem is greatest for 'K-selected' species with low fecundity, and is less of an issue for 'r-selected' species with high fecundity. Haldane attempts

to make quantitative the fairly obvious statement that natural selection cannot occur with great intensity for a number of characters at once unless they happen to be controlled by the same genes.

In the case of selection on peppered moths, if "ten other independently inherited characters had been subject to selection of the same intensity as that for colour, only

(

1

/

2

)

10

{\displaystyle (1/2)^{10}}

, or one in 1024, of the original genotype would have survived." The species would most likely have become extinct; but it might well survive ten other selective periods of comparable selectivity, if they happened in different centuries.