Efforts have been dedicated to the understanding of social-ecological systems, an important focus in ethnobiological studies. In particular, ethnobiological investigations have found evidence and tested hypotheses over the last 30 years on the interactions between human groups and their environments, generating the need to formulate a theory for such systems. In this article, we propose the social-ecological theory of maximization to explain the construction and functioning of these systems over time, encompassing hypotheses and evidence from previous ethnobiological studies. In proposing the theory, we present definitions and two conceptual models, an environmental maximization model and a redundancy generation model. The first model seeks to address biota selection and its use by human populations. The second emphasizes how the system organizes itself from the elements that were incorporated into it. Furthermore, we provide the theoretical scenario of plant selection and use from an evolutionary perspective, which explicitly integrates the phylogenetic relationships of plants (or other living resources) and human beings.