Mayan morality: an exploration of permissible harms.

Anthropologists have provided rich field descriptions of the norms and conventions governing behavior and interactions in small-scale societies. Here, we add a further dimension to this work by presenting hypothetical moral dilemmas involving harm, to a small-scale, agrarian Mayan population, with the specific goal of exploring the hypothesis that certain moral principles apply universally. We presented Mayan participants with moral dilemmas translated into their native language, Tseltal. Paralleling several studies carried out with educated subjects living in large-scale, developed nations, the Mayan participants judged harms caused as the means to a greater good as more forbidden than harms caused as a side-effect (i.e., side-effect bias). However, unlike these other populations living in large-scale societies, as well as a more educated and less rural Mayan comparison group, the target rural Mayan participants did not judge actions causing harm as worse than omissions (i.e., omission bias). A series of probes targeting the action-omission distinction suggest that the absence of an omission bias among the rural Mayan participants was not due to difficulties comprehending the dilemmas, using the judgment scale, or in attributing a greater causal role for actions over omissions. Thus, while the moral distinction between means and side-effect may be more universal, the moral distinction between actions and omission appears to be open to greater cross-cultural variation. We discuss these results in light of issues concerning the role of biological constraints and cultural variation in moral decision-making, as well as the limitations of such experimental, cross-cultural research.

Rapid acquisition of an alarm response by a neotropical primate to a newly introduced avian predator.

Predation is an important selective pressure in natural ecosystems. Among non-human primates, relatively little is known about how predators hunt primate prey and how primates acquire adaptive responses to counteract predation. In this study we took advantage of the recent reintroduction of radio-tagged harpy eagles (Harpia harpyja) to Barro Colorado Island (BCI), Panama to explore how mantled howler monkeys (Alouatta palliata), one of their primary prey, acquire anti-predator defences. Based on the observation that harpies follow their prey prior to attack, and often call during this pursuit period, we broadcast harpy eagle calls to howlers on BCI as well as to a nearby control population with no harpy predation. Although harpies have been extinct from this area for 50-100 years, results indicate that BCI howlers rapidly acquired an adaptive anti-predator response to harpy calls, while showing no response to other avian vocalizations; howlers maintained this response several months after the removal of the eagles. These results not only show that non-human primates can rapidly acquire an alarm response to a newly introduced predator, but that they can detect and identify predators on the basis of acoustic cues alone. These findings have significant implications both for the role of learning mechanisms in the evolution of prey defence and for conservation strategies, suggesting that the use of 'probing' approaches, such as auditory playbacks, may highly enhance an a priori assessment of the impact of species reintroduction.