Stasis (Paleontological)

Stasis is the most counterintuitive and most empirically robust finding of punctuated equilibrium theory. Rather than exhibiting the continuous morphological change that gradualist models predict, the fossil record shows that species typically persist in essentially the same form across the vast majority of their geological duration — often millions of years. This stability is not evolutionary stagnation or genetic invariability. Populations during stasis exhibit normal levels of variation at any given moment, but that variation is pulled back toward a stable mean generation after generation. The stabilizing forces are ecological: species occupy niches constituted by complex webs of relationships, and morphological change risks disrupting those relationships. The cost of change exceeds the cost of stability. The species is locked into its configuration not by inability to evolve but by integration into a system that suppresses evolutionary change. Stasis is data, not noise — the primary pattern that evolutionary theory must explain.