A MODEL OF MACROEVOLUTION AS A BRANCHING PROCESS BASED ON INNOVATIONS

We introduce a model for the evolution of species triggered by generation of novel features and exhaustive combination with other available traits. Under the assumption that innovations are rare, we obtain a bursty branching process of speciations. Analysis of the trees representing the branching history reveals structures qualitatively different from those of random processes. For a tree with n leaves generated by the introduced model, the average distance of leaves from root scales as (log n)2 to be compared to log n for random branching. The mean values and standard deviations for the tree shape indices depth (Sackin index) and imbalance (Colless index) of the model are compatible with those of real phylogenetic trees from databases. Earlier models, such as the Aldous' branching (AB) model, show a larger deviation from data with respect to the shape indices.