Primates and the roots of cognition

When it comes to explaining the brain power of different primates, one theory focuses on social intelligence, which suggests that the complex social structures of each species causes an evolutionary pressure on developing cognition. This is backed up by positive correlations between brain size and markers of social complexity for different primates. Humans, out of all the primates, are considered ultrasocial and possess cognitive abilities beyond that of any of our hairier relatives. 苏州美睫美甲

Human cognition depends on transmitted behaviors—the skills we use in adult life in society, we learn as children. The cultural intelligence hypothesis postulates that humans have a species-specific set of social-cognitive skills that other higher primates don't have that allows us to more readily learn from others. For the first time, this cultural intelligence hypothesis has been tested, and the results published in Science1.

The researchers conducted a series of cognition tests on a group of young children, chimpanzees, and orangutans. The tests were designed to differentiate between the cultural intelligence hypothesis and the general intelligence hypothesis that predicts that humans are simply more intelligent than other primates.

The experiments sought to examine intelligence as it relates to the physical world (spatial memory, tool use, etc) and also to the social world (social learning, comprehension, intentions, etc). Interestingly, the human subjects only did significantly better in the latter series of tests, but the chimps and orangutans were as adept at the physical world tests as the infants. This provides support for the cultural intelligence hypothesis, suggesting that humans have evolved specific social-cognitive skills relevant to exchanging knowledge between individuals in cultural groups.

Science contains another paper on cognition in primates, this time on the ability of nonhuman primates to demonstrate reasoning2. As humans, we are able to use an individual's actions to infer or extrapolate something about their mental state, but it's not known whether this is a specifically human trait. In this study, researchers sought to understand whether or not different species of primate were able to make inferences from a demonstrated behavior.

The primates were presented with a pair of containers potentially containing food. A demonstrator would then gesture intentionally to the one containing food, or unintentionally, in order to determine whether the primate could infer the reasoning behind the demonstrator's actions. In the first test, the demonstrator would either intentionally grasp the one containing food, or flop their hand down in an accidental manner. A second set of experiments involved the demonstrator touching the correct container with their elbow, as they had both hands occupied, versus using their elbows despite having an empty hand. Distinguishing between these gestures suggests an inference of intention by the demonstrator, for example using his elbow as both hands were busy, or rationally grasping a container instead of accidentally touching it.

Three different species of primates were used, representing old world monkeys, new world monkeys, and apes. These groups of primates last shared a common ancestor with man around 40 million years ago, 20 million years ago, and ten million years ago, respectively. Prior research with human infants has shown they have the capacity to distinguish between intentional and rational behavior as compared to more accidental behavior. The researchers found that, like human infants, all three species of primate tested had the ability to discriminate between the intentional and seemingly unintentional actions of the demonstrator, suggesting that the cognitive skill to infer another individual's intentions dates back at least 40 million years into our history as a species.

1 Science, 2007. DOI: 10.1126/science.1146282

2 Science, 2007. DOI: 10.1126/science.1144663