Haldane’s cost of selection imposes a mild constraint on adaptation, with a high proportion of deaths in A. thaliana being selective

Haldane9s Dilemma refers to the concern that the need for many "selective deaths" to complete a substitution creates a speed limit to adaptation. However, discussion of this concern has been marked by confusion over which features of substitutions produce limits to the speed of adaptation, what those limits are, and the consequences of violating speed limits. The term 9substitution load9 has been particularly unhelpful in this regard. Here we distinguish different lines of reasoning that lead to speed limits, including one line of reasoning which has not yet been fully addressed. We then apply these lines of reasoning to a dataset measuring survival and fecundity of 517 different genotypes of Arabidopsis thaliana grown in eight different environmental conditions. We estimate highly permissive limits to the speed of adaptation in all environmental conditions. We also estimate that much higher proportions of deaths contribute to adaptation than were anticipated during historical discussions of speed limits.