An evaluation of stabilizing selection as a mechanism for stasis

In this paper we evaluate the role that stabilizing selection plays in mediating the long term stasis of species. We present a case study from the fossil record which questions the prominent role of stabilizing selection as a mechanism for stasis. We also discuss an alternative mechanism for stasis based on how species are organized in nature, which predicts that as long as a species occurs in several different environments it will be buffered against net change. We conclude that evolutionary and ecological theory indicate that stabilizing selection will only play an important role in maintaining stasis in species if communities are at equilibrium and/or the physical environment is stable over long periods of time. Currently, most data indicate that neither of these is likely, though the recent documentation of long term stability in the Paleozoic faunas of New York State, the phenomenon of coordinated stasis, could conceivably be correlated with some sort of stable ecological entities, possibly a stable community structure. However, in the case of one of these faunas, the Middle Devonian Hamilton Group, patterns of morphological stasis in species appear to be unrelated to stabilizing selection. This implies either that the stability of the Hamilton Group fauna is not equivalent to a set of stable communities, or, even if it is, then at equilibrium stabilizing selection is not an important mechanism mediating stasis.