Be nice to me or I might not talk to you. Or worse, maybe I will talk to you...

Recently published research shows that individual humans will be nicer (more altruistic) when there is the possibility that the recipient of an act can respond verbally. The paper, "Anticipated verbal feedback induces altruistic behavior" is published in Evolution and Human Behavior for March.

These results are not particularly surprising, but it is important to confirm these things through experimental work. From the abstract:

[Humans may be...] motivated by concerns for praise and blame. ... we experimentally investigate the impact of anticipated verbal feedback on altruistic behavior. We study pairwise interactions in which one subject, the "divider," decides how to split a sum of money between herself and a recipient. Thereafter, the recipient can send an unrestricted anonymous message to the divider. The subjects' relationship is anonymous and one-shot to rule out any repeated interaction effects. Compared to a control treatment without feedback messages, donations increase substantially when recipients can communicate. With verbal feedback, the fraction of zero donations decreases from about 40% to about 20%, and there is a corresponding increase in the fraction of equal splits from about 30% to about 50%. Recipients who receive no money almost always express disapproval of the divider, sometimes strongly and in foul language. Following an equal split, almost all recipients praise the divider. The results suggest that anticipated verbal rewards and punishments play a role in promoting altruistic behavior among humans.

The results, graphically:

Apparently, there is a tendency under different conditions to give either nothing or half of the money. Given the strength of this tendency one has to wonder about the individuals who picked strange amounts, like 70 percent. In any event, the key finding here is that under conditions where feedback was going to happen, the "dictator" (divider of the money) more often gave away half of the cash.

The results of this study are supported by other research, such as a similar experiment by Xiao and Houser (2005).

Our findings demonstrate that anticipated verbal feedback in the form of anonymous written messages induces a substantial increase in altruistic behavior towards otherwise defenseless opponents. Since an anonymous written message is a mild form of feedback compared to naturally occurring personal communication, the identified effect is likely to underestimate the behavioral impact of anticipated emotional feedback in more realistic settings.

The authors go on to identify the proximate mechanism for this behavior as a "symbolic award" that fits into the broader social context of award vs. shame. Placing this in an evolutionary context (to seek an 'ultimate' explanation) involves reference to Dan Fessler's work on shame as a powerful mechanism for shaping behavior.

Are these researchers just waving their arms about in a post-hoc Panglossian explication of otherwise uninteresting human behavior? Maybe. But they do practice what they preach. Check out their acknowledgments:

We praise Emma Mårtensson and Björn Tyrefors for their research assistance and two anonymous referees and an editor for their helpful comments. We also express our gratitude to the Torsten and Ragnar Söderberg Foundation, the Jan Wallander and Tom Hedelius Foundation, and the Swedish Research Council for financial support. The authors accept blame for any remaining errors or omissions.

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Source:
OGORMAN, R., WILSON, D., MILLER, R. (2008). An evolved cognitive bias for social norms. Evolution and Human Behavior, 29(2), 71-78. DOI: 10.1016/j.evolhumbehav.2007.07.002

See also:

Fessler, 1999 D.M.T. Fessler, Toward an understanding of the second order emotions. In: A.L. Hinton, Editor, Biocultural approaches to the emotions, Cambridge University Press, New York (1999).

Fessler, 2004 D.M.T. Fessler, Shame in two cultures: Implications for evolutionary approaches, Journal of Cognition and Culture 4 (2004), pp. 207-262.

Xiao and Houser, 2005 E. Xiao and D. Houser, Emotion expression in human punishment behavior, Proceedings of the National Academy of Sciences 102 (2005), pp. 7398-7401.