Comment on “The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals”

sister species to estimate that recent rates of speciation decline toward the tropics. However, this conclusion may be undermined by taxonomic biases, sampling artifacts, and the sister-species method, all of which tend to underestimate diversification rates at low latitudes. Weir and Schluter (1) examined therelationship between time to diver-gence and latitude in sister species of New World birds and mammals. They con-cluded that the slowest recent rates of speciation occur at low latitudes, thus contradicting the widespread view that rapid diversification plays a role in generating tropical diversity (2, 3). However, their findings rest heavily on current taxonomy and phylogenetics, which are subject to latitudinal gradients of their own. Using examples from birds, we show that the apparent slope in rates of speciation can be attributed to biases in data and methods