Why is it that humans are able to act in ways that create significant cost to others even at their own expense? According to Professor Marc Hauser, speaking at the Royal Society today, spite was born out of a combination of cognitive features, unique to man, alongside the ecological and social conditions that led to our forming large societies of unrelated individuals.

Hauser, who is director of the Cognitive Evolution Laboratory at Harvard University, spoke on spite and how the human brain has evolved to make such behaviour possible at a discussion meeting organised by the Royal Society this week. Experts from across the globe gathered to discuss the evolution of social behaviour in micro-organisms, invertebrates, vertebrates and man at the two-day conference.

Based on a review of recent work on human and nonhuman animals, Hauser and his team were able to show that only our own species evolved under conditions that favoured reciprocal altruism and spiteful interactions, and importantly, evolved the brains to carry out such behaviours, even early in life.

Hauser suggests that nonhuman animals don't live in the kinds of societies that would create strong pressure on individuals to require reciprocity to obtain help given that the density of kin is high, and thus, the probability of interacting with them is high as well; in other words, individuals can rely on their kin in times of need.

The same argument is true of spite in nonhuman animals. Hauser says:

"In most cases where an individual does something to impose costs on another, the underlying motivation for such behaviour is selfish. Given that there are so many other ways other than spite to increase one's relative fitness, the costs of spite will very rarely be favoured."

According to Hauser the ability to create interfaces between different psychological processes is the hallmark of our uniquely human cognition. He says:

"Though human thought, like animal thought, is built from modular processes, we have the distinctive capacity to integrate the outputs from these processes to create novel representations, or more generally, novel solutions to old and new problems. We have the capacity to quantify how much money we borrowed (number system), tag the cardinality with a linguistic symbol (language system), take the money and exchange it for some food (economic system), realize that we could have bought it for half the price at a nearby store (number, economics and language), and then experience outrage (emotional system) because the store owner ripped me off (moral system)."

The Royal Society is an independent academy promoting the natural and applied sciences. Founded in 1660, the Society has three roles, as the UK academy of science, as a learned Society, and as a funding agency. It responds to individual demand with selection by merit, not by field. As we prepare for our 350th anniversary in 2010, we are working to achieve five strategic priorities, to:

- Invest in future scientific leaders and in innovation
- Influence policymaking with the best scientific advice
- Invigorate science and mathematics education
- Increase access to the best science internationally
- Inspire an interest in the joy, wonder and excitement of scientific discovery

The Cognitive Evolution Laboratory is part of Harvard University. http://www.wjh.harvard.edu/~mnkylab/Home.html

Marc Hauser is Professor of Psychology, Organismic & Evolutionary Biology and Biological Anthropology. He is Co-Director of the Mind, Brain and Behavior Program, a Fellow of the Center for Ethics and Director of the Cognitive Evolution Laboratory at Harvard University. His research focuses on the evolutionary and developmental foundations of the human mind, with the specific goal of understanding which mental capacities are shared with other nonhuman primates and which are uniquely human.

Nicola Kane
Press and Public Relations
The Royal Society, London