Altruism or association?

Wang and Lu (1) claim to report evidence of a genetic polymorphism of altruistic and nonaltruistic alleles in a natural population of Tibetan ground tits, Pseudopodoces humilis. Their argument assumes that observed heritable variation in altruistic behavior reflects an underlying genetic difference in altruism. However, the authors do not show genetic evidence of an underlying difference, and there is another interpretation of their results. The observed difference in altruism could be the consequence of a genetic difference in the tendency to join groups, because joining groups is a necessary prerequisite to expressing altruism. Thus, the heritable difference may only be in the tendency to associate, or enter the contexts within which social actions like altruism are usually expressed (2).

What Wang and Lu (1) actually measure is how often birds join groups or nest alone. Their claim about altruism rests on the argument that only birds that join nests can “ever” help, while those that do not join never help. However, Wang and Lu do not show that birds that never help lack the genes for altruism. By analogy, one might find that only some chameleons ever turn green, while others never do. However, if some never turn green only because they avoid green foliage, and all chameleons can turn green, the difference in “greenness” would be environmental, not genetic. Similarly, all birds in Wang and Lu’s study could be altruistic in the same way, differing only in their propensity to associate.

By conflating “altruism” and “association,” Wang and Lu (1) perpetuate what Hamilton (3) called “one of the most common misinterpretations” of his theory (4): that it predicts a dynamic equilibrium of indiscriminate altruists and nonaltruists. A recent reincarnation of this misinterpretation is that rb = c could explain the coexistence of altruism strategies across species (1, 5). Unless one confuses altruism and association when interpreting data (1), however, there is little to explain. Even in systems where nonaltruistic types were thought to coexist with altruists in nature, there is little evidence for them (6). Instead, one finds, as Hamilton predicted (4), that all individuals act “basically the same” (3) in a discriminating nepotistic (or “facultative cheating”) fashion (7–9).

Why then, does rb = c apparently explain the variation in association behavior? One possibility is that it does not. Wang and Lu’s (1) study focuses on a single population, representing one data point for comparative study. Previous studies showed that broad comparisons can bring fundamental new insights to particular situations (10). Some evidence suggests that this could be the case here, because applying Hamilton’s rule to association may cause failures (9). Hamilton (4) did not apply inclusive fitness reasoning to explain hymenopteran foundress associations, but reserved it for explaining reproductive decisions or harming behaviors within those associations. It could be that “automatic” effects of association, independent of social actions like altruism (9), are important for explaining association. Unfortunately, these effects—which often depend on ecology (4, 9)—may be obscured by terminology that equates association and altruism.