ABSTRACT
After a section discussing the eect of mutation on networks, the approach taken is explicitly evolutionary, attempting to answer questions of the general form: if a pair of organisms diers in some feature that derived from a common ancestor, what would have been the nature of the variation that achieved these dierent phenotypes? Indeed, if an extant organism diers from the common ancestor in some very specic way, a similar question
can be asked. Although this is not a standard way of approaching variation, it has some qualitative similarities to the far more quantitative approach of phylogenetics (Chapter 8), which attempts to identify the most likely common ancestor sequence that could have generated contemporary ones, and the way in which this happened.
