The primary outcome of natural selection is adaptation to an environment. The primary concern of epistemology is the acquistion of knowledge. Evolutionary epistemology must therefore draw a fundamental connection between adaptation and knowledge. Existing frameworks in evolutionary epistemology do this in two ways; (a) by treating adaptation as a form of knowledge, and (b) by treating the ability to acquire knowledge as a biologically evolved adaptation. I criticize both frameworks for failing to appreciate that mental representations can motivate behaviors that (...) are adaptive in the real world without themselves directly corresponding to the real world. I suggest a third framework in which mental representations are to reality as species are to ecosystems. This is a many-to-one relationship that predicts a diversity of adaptive representations in the minds of interacting people. As “species of thought”, mental representations share a number of properties with biological species, including isolating mechanisms that prevent them from blending with other representations. Species of thought also are amenable to the empirical methods that evolutionists use to study adaptation in biological species. Empirical studies of mental representations in everyday life might even be necessary for science to succeed as a normative “truth-seeking” discipline. (shrink)