Does lack of evolvability constrain adaptation? If so, on what time scales?

The relevance of genetic constraints for evolutionary change beyond microevolutionary timescales is debated. The high evolvability of natural populations predicts rapid adaptation, but evolvability is often found to correlate with phenotypic divergence on longer timescales, which makes sense if evolvability constrains divergence. This chapter attempts to reconcile the observation of high evolvability of populations with the idea that genetic constraints may still be relevant on long timescales. We first establish that a relationship between evolvability and divergence is a common empirical phenomenon both among populations within species (microevolution) and among species (macroevolution). We then argue that a satisfactory model for the prevalence of this empirical relationship is lacking. Linking microevolutionary theory with the dynamics of the adaptive landscape across time—moving toward a proper quantitative theory of phenotypic change on macroevolution timescales— is key to better understanding the relative importance of genetic constraints on phenotypic evolution beyond a handful of generations.