Re: Punctuated Equilibrium Theory

Eliezer S. Yudkowsky (
Wed, 23 Sep 1998 17:29:23 -0500

Robin Hanson wrote:
> and the key assumption is that "the phenotypic optimum changes suddenly and
> then remains fixed during the bout of adaptation studied." The paper then
> models a hill-climbing search to a peak. In such searches, one makes big
> moves early on, and then smaller and smaller moves as one approaches the
> peak.
> As genes get fixed along the way, the genotype ends up reflecting this
> distribution of moves; some genes embody very large moves and others
> very small moves. The paper notes that you don't get this effect "if the
> phenotypic optimum perpetually drifts, moving away from the population at
> about the same rate that the population evolves to `keep up.'"
> The bottom line is that this paper *assumes* punctuated equilibrium,
> and so is not evidence in favor of it.

Punctuated equilibrium is something that needs to be explained because of geological evidence. Postulating it is not a problem. In fact, I would say the major problem with punctuated equilibrium is explaining it to the loony-toon creationists.

As I understand it, the innovation is in explaining the punctuated equilibrium in terms of an exponentially distributed mixture of large and small tweaks. The default explanation is large environmental shifts that increase the selectivity pressures. Another interesting explanation is a continually churning pool of small mutations with some synergetic combinations. The pool keeps churning until the mutation has a sufficiently large chance of meeting up with its synergetic "mate", and then the mutation rapidly becomes dominant throughout the pool. (This one is also based on computer simulations; the key percentage is 14% of the population, or the reciprocal of e squared.) Personally, I think that all three explanations describe real phenomena.

Punctuated equilibrium, as the fossil-record phenomenon, neither requires nor prohibits single big-win mutations. It is not even necessarily relevant to the trajectory of a seed AI, since most theories have nothing to do with the shape of the "hill" one is attempting to climb, or revolve around resistance barriers that aren't relevant to intelligent design. I noticed that paper because it explained punctuated equilibrium in a way that exported fairly well to breakthrough/bottleneck AI trajectories. It was the first explanation I had seen with that property.

--         Eliezer S. Yudkowsky

Disclaimer:  Unless otherwise specified, I'm not telling you
everything I think I know.