Page "Evolutionary developmental biology" Paragraph 28

The discovery of the homeotic Hox gene family in vertebrates in the 1980s allowed researchers in developmental biology to empirically assess the relative roles of gene duplication and gene regulation with respect to their importance in the evolution of morphological diversity.

Several biologists, including Sean B. Carroll of the University of Wisconsin – Madison suggest that " changes in the cis-regulatory systems of genes " are more significant than " changes in gene number or protein function ".

These researchers argue that the combinatorial nature of transcriptional regulation allows a rich substrate for morphological diversity, since variations in the level, pattern, or timing of gene expression may provide more variation for natural selection to act upon than changes in the gene product alone.