Does evolution require selection?
(context can be found in this comments thread on Sandwalk)
Update 16.11.09: I've mentioned this in the comments, but it's kind of a new question so I'll repost it here:
An evolutionary system, regardless of its medium (biological, linguistic, cultural, etc), has finite resources, and must abide by laws of physics. The former necessitates some form of positive selection eventually, the latter invokes negative selection right from the start, provided variation exists. Some forms will end up being unable to self-propagate, regardless of which system we are dealing with. In the biological system this is very obvious - fuck up DNA replication, and the organism's lineage ends there.
My question was invoked partly by the commonly accepted statement that evolution fundamentally requires three things: Heredity, Variation, Selection. As much as I like fighting commonly accepted statements, this one seems strong thus far. Also, I've heard strong proponents of Neutral Theory use these preconditions as fact, so it's not in any way conflicting with a more neutral view of evolution. So I referred to it in the discussion on Larry Moran's blog, and the selection component, to my surprise, was shot down entirely.
So I often hear that evolution is change in allele frequencies (or their equivalent in non-biological systems) over time. Can this change occur without positive selection? Well, yeah, we've got genetic drift. But what about negative selection? Surely, for allele frequencies to shift, the population size must be finite; else the proportions would remain the same (ignoring positive selection). Stuff must die. Even if we assume no selection at that level, the new variation must be 'proof-checked' via negative selection, especially considering many changes are actually deleterious.
I guess if we remove all mutation, then we could have a system devoid of any selection, where stuff just randomly dies and then the allele frequencies would drift, and evolution can be said to occur.
But then, would weather patterns be an evolutionary system? They can be argued to be heritable in a non-discrete sense. Say we have each sq km being rainy, sunny, foggy or whatever. It inherits its next weather state partially from its previous condition (and obviously influenced by neighbours; lets call it LGT). The percentage of sq km in a given population experiencing rain or shine changes randomly selection-wise (although non-randomly if we consider it from the physics perspective; but the same applies to biology).
I'll argue here that, unless I've missed something, the weather system is akin to the biological system minus selection (the variation and heredity are still there). Does it still evolve?
(and thanks, this discussion is really helping me wrap my head around certain things! I don't learn well by just listening and digesting; I have to constantly prod at stuff until I'm ready to accept it!)