Just How Much is the G-matrix Actually Constraining Adaptation?

The genetic variance–covariance matrix (G) has long been considered to summarize the genetic constraints biasing evolution in its early stages, although in some instances, G can enhance divergence and facilitate adaptation. However, the effects of G on the response to selection might be of less importance than previously thought. In addition, it has been suggested that selection itself, under certain conditions, might rapidly alter the genetic covariance structure. If selection can indeed affect the stability of G to facilitate evolution, the overall structure of G might not be as important to consider as the past selective conditions that G was subject to. Thus, more empirical work is needed on the stability of G in the early stages of divergence before one can really assess to what extent G constrains evolution.