COMPUTING SCIENCE
Experimental Lamarckism
Brian Hayes
The Evolution of Evolution
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, was
treated badly by his contemporaries and worse by history. At the
Muséum d'Histoire Naturelle he held the lowliest
professorship, namely Professor of Insects and Worms, but he turned
this academic insult to good advantage, establishing the division
between vertebrate and invertebrate animals. And he devised a theory
of speciation through gradual evolution 60 years before Darwin
published his Origin. Today, however, Lamarck is remembered
only for his great error—his thesis that evolution works by
the transmission of traits acquired through habits of use or disuse.
The idea must have seemed irresistible. If you play a lot of
basketball, Lamarck says, you'll have taller children. And he
appears to be right: The children of basketball players surely
are taller than average. Likewise, if you want your
children to get into Harvard, go to Harvard yourself; the high rate
of acceptance for children of alumni argues that education too is
heritable. The fallacy in this reasoning is now plain, and no one
would propose a Lamarckian mechanism to explain such correlations.
Nevertheless, the suspicion lingers that if only the world
did work Lamarck's way, it would work a little better.
The Harvard basketball team is not the most convenient context for
a computer model of Lamarckian evolution. In searching for a simpler
system, I have been inspired by the famous case of the melanic moths
in industrial Britain. Dark-pigmented forms of the peppered moth
Biston betularia were first noticed in the 19th
century; they grew in abundance for several decades and then receded
again after the 1950s. The cause of the original color shift was
apparently the darkening of tree trunks by coal soot, which impaired
the camouflage of lighter moths and left them exposed to predators.
The later reversal of the trend coincided with measures to reduce
air pollution.
My model of these events is highly abstract, with all the
naturalistic details stripped away. It is not meant to reveal
anything new about melanic moths but merely uses the idea of
selection based on camouflage to explore some mechanisms of
adaptation. The computer model is written in the programming
language StarLogo, created by Mitchel Resnick of the Massachusetts
Institute of Technology. (I discussed StarLogo in the
January-February, 1999, "Computing Science" column.) For
this project I employed StarLogoT, a variant developed by Uri
Wilensky of Tufts University. The model and additional technical
details are available here.
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