BURIAN, R.M.: Modularity, Development, and Genotype-Phenotype Maps

In this paper I examine some surprising consequences of recent results concerning the modularity of the genotype and about the importance of higher-level modules in delimiting body segments. Combining some of these findings with a characterization of genes, at the molecular level, as being nothing but sequences of nucleotides, I argue that some of the hopes that genotype-phenotype maps could solve fundamental problems in evolutionary biology – and perhaps developmental biology as well – are in deep trouble. More specifically, three factors, taken together, may be used to challenge the determinateness of gene products and of the net phenotypic effect of (sequence-defined) genes. These factors are: evolutionary and developmental tinkering with sub-genic modules, post-transcriptional processing of gene products, and the recycling, within development, of various sorts of control modules. Given all three of these factors, the consequences of possession of a particular nucleotide sequence is so context sensitive that analysis at a supra-genomic level is required to ascertain its products and to estimate the phenotypic effects of possession of that nucleotide sequence. This paper is devoted to examining some consequences of this sort of context sensitivity, and to drawing out some implications for attempts to understand evolutionary innovations and (time permitting) the integration of metazoan bodies.