Duplication with variation: Metameric logic in evolution from genes to morphology

This paper discusses the use of duplicated structures in evolution. Duplication, followed by variation and modification of function, has been a major strategy from the time of the early biological molecules to the evolution of advanced morphological complexity. Evolution by duplication with variation produces a hierarchically structured organizational logic based on nested segments, or metameres. The genome is itself largely structured in this way by the process of gene duplication. Duplicate genes often maintain related function and even chromosomal arrangement, and the expression of those related genes may be coordinated, often by regulatory genes, which are themselves the products of gene duplication. The morphology of complex metazoan organisms has evolved in a metameric way from early in evolution, by the use of repeat units in histology and repeated morphological segments. Recent advances in genetics have shown that there is a direct correspondence between these morphological structures and metameric structures in the genome, suggesting how complex morphology was produced by evolution at the gene level. Examples from invertebrates and vertebrates show that homologous processes are involved in morphogenesis in both groups, with strictly homologous developmental genes retaining very similar function and regulation. These issues are highly relevant to an improved understanding of macroevolution and to the core questions of biological anthropology. The evolution of dental morphology is discussed as an example.