2006 | Mo Costandi

It was previously thought that imitation is a capacity that is unique to humans and, perhaps, the great apes. In the current issue of PLoS Biology, Ferrari et al report that the macaque (an Old World monkey species) can imitate the facial movements of humans:

In the third day of life, infant macaques imitate lip smacking and tongue protrusion…These imitative responses…are apparently confined to a narrow temporal window….Neonatal imitation may serve to tune infants’ affiliative responses to the social world. Our findings provide a quantitative description of neonatal imitation in a nonhuman primate species and suggest that these imitative capacities, contrary to what was previously thought, are not unique to the ape and human lineage. We suggest that their evolutionary origins may be traced to affiliative gestures with communicative functions.

The temporal window mentioned in the abstract apparently lasts only a few days, so that by the time the monkeys are 7 days old, they have lost the imitative capacity. Significantly, the window is longer in humans and apes, although in these species the onset of the window is later. The authors also suggest that mirror neurons are responsible for the monkeys’ imitative behaviour.

This clip shows a 3-day-old macaque imitating a researcher:

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Researchers from the Max Planck Institute have discovered that humans and great apes use the same cognitive strategy to remember the location of objects.

Daniel Haun and his colleagues compared spatial memory in great apes and human infants. Spatial memory is the process by which information about one’s environment and its spatial orientation is stored. Several different strategies can be employed to remember where something is located. One of these strategies involves remembering the features of an object; the other involves remembering the object’s location. Most organisms use both strategies, but prefer one over the other if the conditions for recalling the information put those strategies in opposition.

Haun’s team compared the strategies employed by humans and great apes (chimpanzees, bonobos, gorillas, and orangutans) to remember where items had been hidden. Items were hidden in one of two ways – they were either kept in the same place but hidden under a different object, or moved to a different place altogether.

It was found that 1-year-old human infants and all the species of great apes preferred place over feature. This was demonstrated by the observation that, regardless of how the objects had been hidden, both the infants and the apes looked for them objects in the location that they had last seen them. This suggest that great apes and humans inherited the preferred spatial memory strategies from a common ancestor some 15 million years ago.

However, 3-year-old infants preferred using the objects under which items had been hidden. The continuity in spatial memory strategies between humans and great apes therefore seems to be overridden by the cognitive developmental processes that take place in humans after the age of 1.

“The unique human cognitive development seems to mask some of our evolved strategies even before we reach the age of three,” says Haun, who is lead author of a paper in Current Biology describing the work. “In future,” he continues, “we want to find out which areas of cognitive development in humans…are responsible for this restructuring of cognitive preferences.”

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Mo Costandi

Neuroscience writer

Yearly Archives: 2006

Monkeys ape man

A cognitive strategy shared by humans & great apes