Haldane's Dilemma and the Cost of Natural Selection
Adaptation requires a new genotype to fully replace a population of individuals with different genotypes, and this replacement process imposes a cost on the population. J.B.S. Haldane quantified this cost in terms of deaths the population sustains in order for a new genotype to fully replace a population. Since populations can only sustain so many deaths per generation without going extinct, the cost imposed by natural selection sets an upper bound to the rate at which adaptation can proceed. This speed limit on adaptation is known as Haldane's Dilemma. The correct way to calculate this speed limit and whether existing populations break this speed limit or not have been the subject of a great deal of controversy and confusion. We clarify an important way to quantify the cost of natural selection in terms of reproductive excess, and explore Haldane's Dilemma and the cost of natural selection using an extensive dataset of Arabidopsis thaliana, collected by Exposito-Alonso et al. 2019.