method for testing adaptive hypotheses. In the simplest case, test for a correlation between two traits or between a trait and an environment variable across population - or naturally occurring population between groups. Problems - Data availability (enough populations studied?), Data quality (How many individuals?), inferring causality from correlation (can you infer the direction of change), Non-independence among populations.

A research method in which one makes systematic comparisons among different species in order to gain insights into the function of a particular structure or behavior, or the evolutionary origins of that structure or behavior.

The study of adaptation by comparing many species.

the comparison of people's experiences of different types of social structure or social setting in terms of historical points in time, or across cultures at a single point in time. This is an approach which can shed light on the particular arrangements of both sides of the comparison. (see also constant comparison in index)

The approach to diachronic linguistics in which the researcher analyzes either several daughter languages of the same ancestor or several stages in the history of one language in order to describe the linguistic development of that language over time.