The Ancestral Co-Evolution A. A simple example of a co-evolving forest with three trees (each tree corresponds to a different gene family), and one co-evolution edge connecting node x2 in tree T1 and node y2 in tree T2; the weight table corresponding to this co-evolution edge is in red. The weight table corresponding to the tree edge (x1, x2) in T1 is in green. The values at the leaf x5 in tree T1 and the leaf y5 in tree T2 are missing. B. The co-evolutionary graph corresponding to the co-evolving forest in A.