How does genome evolution affect the rate of diversification of biological lineages? Recent studies have suggested that the overall rate of genome evolution is correlated with the rate of diversification. If true, this claim has important consequences for understanding the process of diversification, and implications for the use of DNA sequence data to reconstruct evolutionary history. However, the generality and cause of this relationship have not been established. Here, we test the relationship between the rate of molecular evolution and net diversification with a 19-gene, 17-kb DNA sequence dataset from 64 families of birds. We show that rates of molecular evolution are positively correlated to net diversification in birds. Using a 7.6-kb dataset of protein-coding DNA, we show that the synonymous substitution rate, and therefore the mutation rate, is correlated to net diversification. Further analysis shows that the link between mutation rates and net diversification is unlikely to be the indirect result of correlations with life-history variables that may influence both quantities, suggesting that there might be a causal link between mutation rates and net diversification.D iversification is the net result of the addition of species by speciation and the removal of species by extinction. Understanding the causes and consequences of diversification is central to evolutionary biology. Correlations between diversification, life history, and ecology are becoming increasingly well understood (e.g., refs. 1-4). However, the link between diversification and the rate of molecular evolution is still debated, with much of the attention focused on the role speciation plays in driving genetic change (5-13). Changes to specific genes have been linked to the development of reproductive isolation during species formation, and in some cases such genes have been shown to be under strong positive selection (reviewed in refs. 14 and 15). However, there is a growing body of evidence showing that diversification correlates positively with rates of DNA sequence evolution in "house-keeping" genes, which are associated with basic metabolic functions and, therefore, not expected to be directly involved in the process of diversification. These results raise the possibility that there is a general association between diversification and rates of genomic change.Previous studies have noted that clades of flowering plants containing more species tend to have longer molecular branch lengths (6, 11), and that path lengths on molecular phylogenies from a range of taxa tend to be positively correlated to the number of nodes through which they pass (16). These results suggest that net diversification-the balance between speciation and extinction rates that gave rise to the extant diversity-is somehow linked to rates of DNA change over time.One hypothesis put forward to explain the correlation between rates of molecular evolution and net diversification is that the process of speciation increases the rate of molecular evolution (10, 16). This ...

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