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Modularity in Evolution: Some Low-Level Questions

Lee Altenberg

In Modularity: Understanding the Development and Evolution of Complex Natural Systems, Werner Callebaut and Diego Rasskin-Gutman, editors. MIT Press, 2005.
Proceedings of the Konrad Lorentz Institute Workshop, Organized by Werner Callebaut and Diego Rasskin-Gutman, October 2000, Altenberg, Austria.

The “function network”, showing the relationship between genes, variables that screen off the gene’s causal effects, and variables that screen off these variables, etc., all the way to fitness components.

I have endeavored in this essay to delve into some of the low-level conceptual issues associated with the idea of modularity in the genotype-phenotype map. My main proposal is that the evolutionary advantages that have been attributed to modularity do not derive from modularity per se. Rather, they require that there be an ``alignment'' between the spaces of phenotypic variation, and the selection gradients that are available to the organism. Modularity in the genotype-phenotype map may make such an alignment more readily attained, but it is not sufficient; the appropriate phenotype-fitness map in conjunction with the genotype-phenotype map is also necessary for evolvability.