Climbing Pit Improbable
In the ongoing Adaptationist v. Pluralist debate, both sides agree on a surprising amount. Both sides agree that there is more to evolution than adaptation by natural selection. However, Adaptationist would argue that adaptation by natural selection is the most important, or even the overwhelming, evolutionary process, and that evolution can be described as climbing Mt. Improbable – with adaptation to environment similar to climbing a fitness landscape peak towards optimal fitness (but please note, never, ever, reaching the top!)
I disagree. I think genetic drift accounts for most of the evolution that occurs, and natural selection, while very important – especially in creating diversity – accounts for a smaller percentage. However, both have worked together to produce the diversity of life on Earth.
I also have a problem with the Mt Improbable analogy . . . well, actually I have two problems.
1) It perpetuates the idea that evolution is an upward striving process, and that derived or adapted groups are higher, than the less derived or less adapted and, as a consequence, fitter, advanced . . .better. (the old Tree of Life analogy problem.)
OK, maybe it is applicable to a fitness landscape, but there is no reason that the landscape has to have the peaks pointing upwards, . . . is there? Surely it's the distance between where you are on the peak and the schmucks on the fitness plane that is important, not the direction of that distance?
Plus, fitness landscapes, are not permanent, or even solid. They change with the environment. A population/species, or whatever, may be quite "high" (see how hard it is to use neutral language)on a fitness peak one minute, and find itself down on the plane, or even in a fitness trough, with hardly any change in allele frequency, but a significant change in environment. In other words the fitness landscape moved underneath it.
2) The real problem with the Mt Improbable analogy though, is that it gives the impression that as hard as it is to ‘climb up’ (and it is), the analogy suggests that it is relatively easier to ‘climb down’ - and it isn’t because its actually harder. OK that might be pushing the analogy a bit far – but that’s the point, it doesn’t hold up to detailed scrutiny.
The real problem is that adaptation, in the broader picture, is an evolutionary cul-de-sac.
Check out the full posting here.