  Concomitant with the evolution of biological diversity must have been the
evolution of mechanisms that facilitate evolution, due to the essentially
infinite complexity of protein sequence space. We describe how evolvability can
be an object of Darwinian selection, emphasizing the collective nature of the
process. We quantify our theory with computer simulations of protein evolution.
These simulations demonstrate that rapid or dramatic environmental change leads
to selection for greater evolvability. The selective pressure for large scale
genetic moves, such as DNA exchange, becomes increasingly strong as the
environmental conditions become more uncertain. Our results demonstrate that
evolvability is a selectable trait and allow for the explanation of a large
body of experimental results.
