Fossils, genes, and the origin of novelty

The origin of evolutionary novelty involves changes across the biological h ierarchy: from genes and cells to whole organisms and ecosystems. Understan ding the mechanisms behind the establishment of new designs involves integr ating scientific disciplines that use different data and, often, different means of testing hypotheses. Discoveries from both paleontology and develop mental genetics have shed new light on the origin of morphological noveltie s. The genes that play a major role in establishing the primary axes of the body and appendages, and that regulate the expression of the genes that ar e responsible for initiating the making of structures such as eyes, or hear ts, are highly conserved between phyla. This implies that it is not new gen es, per se, that underlie much of morphological innovation, but that it is changes in when and where these and other genes are expressed that constitu te the underlying mechanistic basis of morphological innovation. Gene dupli cation is also a source of developmental innovation, but it is possible tha t it is not the increased number of genes (and their subsequent divergence) that is most important in the evolution of new morphologies; rather it may be the duplication of their regulatory regions that provides the raw mater ial for morphological novelty. Bridging the gap between microevolution and macroevolution will involve understanding the mechanisms behind the product ion of morphological variation. It appears that relatively few genetic chan ges may be responsible for most of the observed phenotypic differences betw een species, at least in some instances. In addition, advances in our under standing of the mechanistic basis of animal development offer the opportuni ty to deepen our insight into the nature of the Cambrian explosion. With th e advent of whole-genome sequencing, we should see accelerated progress in understanding the relationship between the genotype, phenotype, and environ ment: post-genomics paleontology promises to be most exciting.