Rational Primates

Source: Harvard University
Date: September 6, 2007


Primates Expect Others To Act Rationally

Science Daily — When trying to understand someone's intentions, non-human primates expect others to act rationally by performing the most appropriate action allowed by the environment, according to a new study by researchers at Harvard University.

The work was led by Justin Wood, a graduate student in the Department of Psychology in the Faculty of Arts and Sciences at Harvard, with David Glynn, a research assistant, and Marc Hauser, professor of psychology at Harvard, along with Brenda Phillips of Boston University.

"A dominant view has been that non-human primates attend only to what actions 'look like' when trying to understand what others are thinking," says Wood. "In contrast, our research shows that non-human primates infer others' intentions in a much more sophisticated way. They expect other individuals to perform the most rational action that they can, given the environmental obstacles that they face."

The scientists studied the behavioral response of over 120 primates, including cotton-top tamarins, rhesus macaques and chimpanzees. These species represent each of the three major groups of primates: New World monkeys, Old World monkeys and apes. All three species were tested in the same way, and the results showed the same responses among the different types.

In the first experiment, the primates were presented with two potential food containers, and the experimenter either purposefully grasped one of the containers, or flopped their hand onto one of the containers in an accidental manner. For all three species, the primates sought the food container that was purposefully grasped a greater number of times than the container upon which the hand was flopped. This indicates that the primate inferred goal-oriented action on the part of the experimenter when he grasped the container, and was able to understand the difference between the goal-oriented and accidental behavior.

In the second experiment, the researchers asked if the primates infer others' goals under the expectation that other individuals will perform the most rational action allowed by the environmental obstacles. Again, the primates were presented with two potential food containers. In one scenario, an experimenter touched a container with his elbow when his hands were full, and in another scenario, touched a container with his elbow when his hands were empty.

The primates looked for the food in the container indicated with the elbow more often when the experimenter's hands were full. The primates considered, just as a human being would, that if someone's hands are full then it is rational for them to use their elbow to indicate the container with food, whereas if their hands are empty it is not rational for them to use their elbow, because they could have used their unoccupied hand.

Developmental psychologists have long understood that young children are able to engage in this type of rational action perception, but scientists have not understood if this ability is unique to human beings, or shared with other animals. This study suggests that this ability evolved as long as 40 million years ago, with non-human primates.

"This study represents one of the broadest comparative studies of primate cognition, and the significance of the findings is reinforced by the fact that these results were consistent across three different species of primates," says Wood. "The results have significant implications for understanding the evolution of the processes that allow us to make sense of other people's behavior."

The findings appear in the Sept. 7 issue of the journal of Science.

The research was funded by the National Institutes of Health, the Guggenheim, and the National Science Federation.

Note: This story has been adapted from a news release issued by Harvard University.

Lost world

University of Birmingham researchers are heralding "stunning" findings as they map the "best-preserved prehistoric landscape in Europe".

This large plain disappeared below the water more than 8,000 years ago.

The Birmingham researchers have been using oil exploration technology to build a map of the once-inhabited area that now lies below the North Sea - stretching from the east coast of Britain up to the Shetland Islands and across to Scandinavia.

'Terrifying'

"It's like finding another country," says Professor Vince Gaffney, chair in Landscape Archaeology and Geomatics.

Map of Doggerland
Prehistoric rivers, hills and valleys are mapped off the east coast
It also serves as a warning for the scale of impact that climate change can cause, he says.

Human communities would have lost their homelands as the rising water began to encroach upon the wide, low-lying plains.

"At times this change would have been insidious and slow - but at times, it could have been terrifyingly fast. It would have been very traumatic for these people," he says.

"It would be a mistake to think that these people were unsophisticated or without culture... they would have had names for the rivers and hills and spiritual associations - it would have been a catastrophic loss," says Professor Gaffney.

As the temperature rose and glaciers retreated and water levels rose, the inhabitants would have been pushed off their hunting grounds and forced towards higher land - including to what is now modern-day Britain.

Map of rising water
The rising water levels began to remake the coastline
"In 10,000 BC, hunter-gatherers were living on the land in the middle of the North Sea. By 6,000 BC, Britain was an island. The area we have mapped was wiped out in the space of 4,000 years," explains Professor Gaffney.

So far, the team has examined a 23,000-sq-km area of the sea bed - mapping out coastlines, rivers, hills, sandbanks and salt marshes as they would have appeared about 12,000 years ago.

And once the physical features have been established, Professor Gaffney says it will be possible to narrow the search for sites that could yield more evidence of how these prehistoric people lived.

These inhabitants would have lived in family groups in huts and hunted animals such as deer.

The mapping of this landscape could also raise questions about its preservation, says Professor Gaffney - and how it can be protected from activities such as pipe-laying and the building of wind farms.