The extended ‘common cause’: causal links between punctuated evolution and sedimentary processes

The common-cause hypothesis suggests that the factors that control the
availability of the Earth’s sedimentary record may also affect
probabilities of speciation and extinction and thus exert
macroevolutionary controls on standing biodiversity.  Here I show
through computational modeling that common causes may also link
sedimentary biases and microevolutionary processes of trait evolution.
 Using Gould’s classic “evolutionary microcosm” of Bermuda and
its diverse endemic clade of land snails, Poecilozonites, I show that the
glacial-interglacial sea level cycles that toggle local sedimentation
between rapid eolian accumulation and slow pedogenesis could easily toggle
trait evolution between rapid bursts of morphological change driven small
effective population size, disruptions in gene flow, and “genetic surfing”
expansion events punctuated with long periods of slow morphological
evolution associated with geographic range coalescence, large effective
population size, and panmixia.  The pattern produced by this
interaction is expected to be similar to that produced by punctuated
equilibria, even without accompanying speciation events.  The
spatial dynamics of this system are expected to produce patterns of random
trait evolution that are more likely multi-rate evolutionary models than
like the standard single-rate Brownian motion models that are currently
used as the null model in many phylogenetic comparative methods.
 The Bermudian example of links between sedimentation and
evolution is arguably extreme, but the principles of the extended common
cause are likely to extend to many other paleontological systems.