The various behavioral disciplines model human behavior in distinct and incompatible ways. Yet, recent theoretical and empirical developments have created the conditions for rendering coherent the areas of overlap of the various behavioral disciplines. The analytical tools deployed in this task incorporate core principles from several behavioral disciplines. The proposed framework recognizes evolutionary theory, covering both genetic and cultural evolution, as the integrating principle of behavioral science. Moreover, if decision theory and game theory are broadened to encompass other-regarding preferences, they become capable of modeling all aspects of decision making, including those normally considered “psychological,” “sociological,” or “anthropological.” The mind as a decision-making organ then becomes the organizing principle of psychology.

The question of reductionism is an obstacle to unification. Many behavioral scientists who study the more complex or higher mental functions avoid regarding them as selected by motivation. Game-theoretic models in which complex processes grow from the strategic interaction of elementary reward-seeking processes can overcome the mechanical feel of earlier reward-based models. Three examples are briefly described.

Unlike physics and chemistry, the behavioral sciences are historical sciences that explain the fuzzy complexity of social life through historical narratives. Unifying the behavioral sciences through evolutionary game theory would require a nested hierarchy of three kinds of historical narratives: natural history, cultural history, and biographical history.

Although the beliefs, preferences, and constraints (BPC) model may account for individuals independently making simple decisions, it becomes less useful the more complex the social setting and the decisions themselves become. Perhaps rather than seek to unify their field under one model, behavioral scientists could explore when and why the BPC model generally applies versus fails to apply as a null hypothesis.

We support the ambitious goal of unification within the behavioral sciences. We suggest that Darwinian evolution by means of natural selection can provide the integrative glue for this purpose, and we review our own work on selective investment theory (SIT), which is an example of how other-regarding preferences can be accommodated by a gene-centered account of evolution.

Gintis's article is an example of growing awareness by social scientists of the significance of evolutionary theory for understanding human nature. Although we share its main point of view, we comment on some disagreements related to levels of behavioral analysis, the explanation of social cooperation, and the ubiquity of inter-individual differences in human decision-making.

The contemporary behavioral sciences are disunified and could not easily become unified, as they operate with incompatible explanatory models. According to Gintis, tolerance of this situation is “scandalous” (sect. 12). I defend the ordinary behavioral scientist's lack of commitment to a unifying explanatory model and identify several reasons why the behavioral sciences should remain disunified for the foreseeable future.

Even if game theory is broadened to encompass other-regarding preferences, it cannot adequately model all aspects of interactive decision making. Payoff dominance is an example of a phenomenon that can be adequately modeled only by departing radically from standard assumptions of decision theory and game theory – either the unit of agency or the nature of rationality.

Behavioral science, unified in the way Gintis proposes, should affect ethics, which also finds itself in “disarray,” in three ways. First, it raises the standards. Second, it removes the easy targets of economic and sociobiological selfishness. Third, it provides methods, in particular the close coupling of theory and experiments, to construct a better ethics.

Gintis assumes the behavioral (=social) sciences are in disarray, and so proposes a theory for their unification. Examination of the unity of the physical sciences reveals he misunderstands the unity of science in general, and so fails to see that the social sciences are already unified with the physical sciences. Another explanation of the differences between them is outlined.

Evolutionary theory provides a firm foundation for the unification of the behavioral sciences, and the beliefs, preferences, and constraints (BPC) model is a useful analytical tool for understanding human behavior. However, evolutionary theory suggests that if other-regarding preferences expressed by humans have evolved under selection, they are ultimately, if not purely, in the constrained, relative self-interests of individuals who express them.

Though capturing powerful analytical principles, this excellent article misses ways in which psychology and neuroscience bear on reciprocity and decision-making. I suggest more explicit consideration of scale. We may go further beyond gene-culture dualism by articulating how varieties of living systems, while ultimately drawing from both genetic and cultural streams, evolve sufficiently as unitary targets of selection to mediate higher-level complex systems.

Game theory provides a descriptive or a normative account of an important class of decisions. Given the cognitive sciences' emphasis on explanation, unification with the behavioral sciences under a descriptive model would constitute a step backwards in their development. I argue for the interdependence of the cognitive and behavioral sciences and suggest that meaningful integration is already occurring through problem-based interdisciplinary research programs.

With a few incisive (and legitimate) criticisms of crucial experiments in psychology that purported to bring down the foundations of modern economics, together with a broad scholarly review that is praiseworthy, Gintis attempts to build a unifying framework for the behavioral sciences. His efforts fail, however, because he fails to break with the conventional methodology, which, regrettably, is the unifying basis of the behavioral sciences. As a result, his efforts will merely recapitulate the story of the past: interesting, provocative results that are soon overthrown because they are limited to the conditions of the experiment. Gintis is keenly aware of this limitation – and thus meets Brunswik, but fails to recognize him; this we know because he seems unaware of the fact that Brunswik said it all – and provided a detailed defense – a half century ago.

For Herbert Gintis, the “rational actor,” or “beliefs, preferences, and constraints (BPC),” model is central to his unifying framework for the behavioral sciences. It is not argued here that this model is refuted by evidence. Instead, this model relies ubiquitously on auxiliary assumptions, and is evacuated of much meaning when applied to both human and nonhuman organisms. An alternative perspective of “program-based behavior” is more consistent with evolutionary principles.

The argument for unifying behavioral sciences can be enhanced by highlighting concrete, vivid, and useful benefits that coherent behavioral models could provide. Shifting sets of behavioral assumptions underlie every legal system's efforts to modify behaviors by changing incentives in the legal environment. Consequently, where those assumptions are flawed, improved behavioral models could improve law's effectiveness and efficiency in regulating behavior.

Gintis argues that disciplinary models of human behavior are incompatible. However, his depiction of the discipline of anthropology relies on a broad generalization that is not supported by current practice. Gintis also ignores the work of cognitive anthropologists, who have developed theories and methods that are highly compatible with the perspective advocated by Gintis.

Psychological science can benefit from a theoretical unification with other social sciences. Social psychology in particular has gone through cycles of repression, denying itself the opportunity to see the calculating element in human interaction. A closer alignment with theories of evolution and theories of interpersonal (and intergroup) games would bring strategic reasoning back into the focus of research.

There are two roadblocks to using game theory as a unified theory of the behavioral sciences. First, there may not be a single explanatory framework suitable for explaining psychological processing. Second, even if there is such a framework, game theory is too limited, because it focuses selectively on decision making to the exclusion of other crucial cognitive processes.

This commentary suggests that an equilibrium framework may be retained, in an evolutionary model such as Gintis's and with more satisfactory results, if rationality is relaxed in a slightly different way than he proposes: that is, if decisions are assumed to be related to rewards probabilistically, rather than with certainty. This relaxed concept of rationality gives rise to probabilistic equilibria.