Punctuated Equilibrium Theory

Robin Hanson (hanson@econ.berkeley.edu)
Wed, 23 Sep 1998 14:10:50 -0700

On 9/10/98 -0500, Eliezer S. Yudkowsky wrote:
>I find it peculiarly coincidental that right after I published my statements
>on punctuated equilibrium, I found this paper on Eurekalert:
>Orr challenges the theory that evolution consists of many tiny genetic
>mutations: "The distribution of mutations causing adaptation neatly fits an
>exponential curve: While few major mutations are needed, the number of more
>minor mutations rises exponentially with their genetic insignificance. Orr's
>theory is based on mathematical modeling and computer simulations, and assumes
>that a population is well-positioned to adapt to environmental pressures. He
>now plans to use a common laboratory technique called quantitative trait
>locus, or QTL, analysis -- capable of examining how species' genetic
>compositions differ -- to examine whether his theory holds up."

I finally obtained this paper and read it last night. It is a theory paper, 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.

Robin Hanson
hanson@econ.berkeley.edu http://hanson.berkeley.edu/ RWJF Health Policy Scholar, Sch. of Public Health 510-643-1884 140 Warren Hall, UC Berkeley, CA 94720-7360 FAX: 510-643-8614