Phylogenetic comparative methods.

Phylogenetic comparative methods (PCMs) enable us to study the history of organismal evolution and diversification. PCMs comprise a collection of statistical methods for inferring history from piecemeal information, primarily combining two types of data: first, an estimate of species relatedness, usually based on their genes, and second, contemporary trait values of extant organisms. Some PCMs also incorporate information from geological records, especially fossils, but also other gradual and episodic events in the Earth's history (for example, trait data from fossils or the global oxygen concentration as an independent variable). It is important to note at the outset that PCMs are not concerned with reconstructing the evolutionary relationships among species; this has to do with estimating the phylogeny from genetic, fossil and other data, and a separate set of methods for this process makes up the field of phylogenetics. PCMs as a set of methods are distinct from, but are not completely independent of, phylogenetics. PCMs are used to address the questions: how did the characteristics of organisms evolve through time and what factors influenced speciation and extinction?