Buy the flashier car or save more for retirement? One marshmallow now or two in fifteen minutes? In the 1960s, the question of how people make decisions across time became a guiding research problem in the social sciences, following two notable trajectories. Economists like Tjalling Koopmans sought to develop a formal-mathematical model of intertemporal choice that could be derived from basic axioms of rational behavior. Simultaneously, psychologists working in the behaviorist tradition, notably Richard Herrnstein—who took over leadership of the famed Harvard Pigeon Laboratory from founder B. F. Skinner in the early 1960s—and Pigeon Lab member George Ainslie, sought to understand inter-temporal behaviors like “impatience” and “impulse control” as measurable empirical phenomena, with pigeons as models. Researchers in both fields contended that the present/future trade-offs humans—and other animals—make could be rendered by a mathematical function. For the economists, this “discounting” curve was exponential, coinciding with the practical compound-interest mathematics long used financiers, actuaries, and engineers. For the psychologists, informed by Herrnstein’s behaviorist “matching law,” this curve was hyperbolic, indicating that animals/humans tended to discount the near-future more heavily than the distant-future. Beginning in the 1980s, the economic and psychological strands began to entangle, and choice over time became a foundational problem in an emergent “behavioral economics.” As previous scholars have noted, this interdisciplinary encounter entailed a clashing and (incomplete) reconciliation of different methodologies, epistemic values, and conceptions of human nature. It also involved another, less noticed, boundary-crossing: the emergence of non-human animals as economic actors.
