Evolving “Metazoan” Development

A paradigm system for the evolution of multicellular animals is constructed. In many evolutionary models, the non-linearity of the genome-phenome mapping is ignored. However, the results of evolutionary paradigm systems that did include a non-trivial, complex genome-phenome mapping have suggested a framework joining seemingly conflicting evolutionary “points of view” like neutral evolution, Punctuated evolution and “gradualism”. The embryonal development of multicellular animals adds many new levels of complexity to the genome-phenome mapping. (1) Genes interact resulting in a differentiated pattern of gene expression: a cell type. (2) Cells interact, generating cellular diversity and pattern. (3) Cells sort out to form tissues and organs. (4) Tissues and organs interact. The first three levels of complexity were included in the paradigm system. Artificial evolution using a trivial fitness criterion resulted in a metastable sequence of epoches, each characterised by a predominant type of development. The evolved “metazoans” successively include in their developmental programs cell polarity, cell-cell communication, cell movement, positional information and genetic redundancy. Prelimary results suggest that the evolved genomes are hierarchically structured. “Regulatory genes”, being highly sensitive to mutation, control the expression of mutationally less sensitive “downstream” genes. It is hypothesised that evolutionary innovations result from mutations in the regulatory genes, whereas small scale changes within epochs result from mutations in the downstream genes.