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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.

Figure 1. Three hypothetical organismsClick to Enlarge Image

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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