There is an interesting article on evolvability which I wrote a bit more about here. It is by Massimo Pigliucci and titled, Is Evolvability Evolvable, for which the whole PDF is available online. Pigliucci discusses definitions of evolvability as well as different ideas about the origins of evolvability.
Here is the abstract:
In recent years, biologists have increasingly been asking whether the ability to evolve — the evolvability — of biological systems, itself evolves, and whether this phenomenon is the result of natural selection or a by-product of other evolutionary processes. The concept of evolvability, and the increasing theoretical and empirical literature that refers to it, may constitute one of several pillars on which an extended evolutionary synthesis will take shape during the next few years, although much work remains to be done on how evolvability comes about.