There’s been a bit of talk about “Evolutionary Speed Limits” over at the Intelligent Design weblog Uncommon Descent. Most of the discussion involves “Haldane’s Dilemma.” This concept is rooted in an article written by the noted evolutionary geneticist J. B. S Haldane in 1957. There’s a lot of math involved, and you can see it over at the Wikipedia page I linked above. The bottom line, for those not interested in the math, is this: according to Haldane’s calculations, a species cannot reasonably fix beneficial mutations (a particular mutation becomes “fixed” when it is present in all of the population) at a rate any faster than 1 mutation per 300 generations.
A number of anti-evolutionists have taken this as evidence against evolution. If, they argue, genetic changes can only be fixed at a rate of 1 per 300 generations, how can evolution possibly explain the differences between species like humans and chimps, where not nearly enough generations have passed to account for the number of differences that we observe. There are a number of problems with using Haldane’s calculations in this way, and in this post I’m going to look at one of those - the one that I think is the most important. For clarity, I should probably make sure that I am very explicit about what, exactly, the problem is before I start, so here it is:
Using Haldane’s 1 substitution per 300 generations as a speed limit for all evolution is wrong because Haldane’s calculations and concerns only apply under certain very specific circumstances.