Reinventing species selection with molecular phylogenies

Species selection as a potential driver of macroevolutionary trends has been relegated to a largely philosophical position in modern evolutionary biology. Fundamentally, species selection is the outcome of heritable differences in speciation and extinction rates among lineages when the causal basis of those rate differences can be decoupled from genotypic (within-population) fitnesses. Here, we discuss the rapidly growing literature on variation in species diversification rates as inferred from molecular phylogenies. We argue that modern studies of diversification rates demonstrate that species selection is an important process influencing both the evolution of biological diversity and distributions of phenotypic traits within higher taxa. Explicit recognition of multi-level selection refocuses our attention on the mechanisms by which traits influence speciation and extinction rates.