Philosophy Ph.D. Dissertations


Motivation Matters: A Critical Analysis and Refutation of Evolutionary Arguments for Psychological Altruism

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)



First Advisor

Michael Bradie


The origin of altruistic behavior has long been a puzzle for evolutionary biologists, beginning with Darwin. Although group selection was first favored to explain cooperative and altruistic behaviors, the forces of individual selection came to be seen as far more prevalent, powerful, and responsive to change. The theory of group selection was replaced by other explanations for altruistic behavior such as kin selection (inclusive fitness theory) and game theory. Recently, however, group selection has been regaining credibility in evolutionary biology. This resurgence is largely due to the work of two of the most prominent proponents of group selection David Sloan Wilson, a biologist, and Eliot Sober, a philosopher of science, who believe evolutionary arguments not only explain the origin of altruistic behaviors but also help resolve the psychological egoism versus altruism debate by providing evidence that natural selection favors altruistic motivations (psychological altruism).

While there is no necessary link between the existence of group selection and altruistic motivation, if Sober and Wilson are right that group selection pressures are nearly ubiquitous for social organisms, this additional selection pressure would mean that cooperative strategies, including true altruism, would be beneficial more often than under a scenario that only includes selection at the individual level. Their argument rests on two evolutionary principles: the direct/indirect asymmetry principle, which posits a mechanism that triggers a fitness-enhancing response by directly detecting a fitness-relevant situation, and the two are better than one argument, which posits that an organism that has multiple mechanisms that serve the same function has a fitness advantage over an organism that has only one of these mechanisms.

While both of these principles are valid, the evolutionary arguments that incorporate them are flawed and the evolutionary arguments arising from them should instead lead to the conclusion that psychological altruism is improbable. Psychological hedonism is a more likely trigger for the most fitness-enhancing degree of behavioral altruism had the chance to become firmly entrenched before psychological altruism could have ever even made an appearance.