How Important Are Gene Expression Changes To Morphological And Physiological Evolution?

In my chapter THE RIDDLE OF THE 1.6% I try to resolve the age-old question of how two closely-related species at the DNA sequence level - humans and chimpanzees - could be so different at the level of morphology, physiology and, of course, cognition. Part of the answer lies in the importance of the evolution of a large number of ways in which gene activity is regulated - how hard genes work to produce protein, and when they do it. But, in a general sense, how important is this phenomenon of gene expression to the evolution of any organism? In this paper, Jianzhi Zhang and colleagues analyze over 5,000 mouse genes, some of which influence morphological features, others physiological ones. They found that "morphogenes" evolve faster in terms of expression than in DNA gene sequence compared to "physiogenes". They "are grossly enriched with transcriptional regulators". This, they say, is because morphogenes are more likely to be essential and pliotropic (affecting more than one morphological aspect of the phenotype) and are less likely to be tissue specific. There is thus an increased likelihood, via sequence evolution, of throwing a genetic spanner into a complex works, which is why gene expression routes to phenotypic change have been favoured.