It's hard to study intelligence in humans — our cultures are incredibly complex, and what counts as "smart" is defined as much by our societies as it is by our genes. So some researchers have turned to chimpanzees to understand what actually gives rise to intelligence in the brain.
A century of scientific investigation into human intelligence has revealed that genes do indeed play an important role in its development, but that cultural and experiential factors can also exert a great amount of control. Intelligence, or IQ – the score on one of several popular, standardized measurements of intelligence – can be modified by an individual's socioeconomic status, for example. A child's early life experiences, such as abusive or neglectful parenting, also impact intelligence. As with most things in psychology, understanding the complex dance of genes and environment becomes confusing, especially since genes and environment can themselves become correlated. One popular way to eliminate those complications is to study animals.
Early Approaches to Animal Intelligence
Animal intelligence has long been of interest to psychologists, ethologists, and anthropologists, but until fairly recently the overwhelming majority of studies has taken a behaviorist approach. It's an approach that largely eschews biology in favor of experience. Think: Skinner and Watson.
It has only been in the last couple decades that animal behavior researchers have begun to think about the socio-biological factors that contribute to animal behavior and cognition, and even more recently that researchers have begun to think seriously about individual differences among animals when it comes to intelligence and cognition.
Now that measurements for non-human intelligence have started to catch up with those that have been developed for understanding human intelligence, researchers are in a position to turn to animals in order to better understand the development of intelligence. Just how important are genes? How much can experience really push things around?
Genes + Environment = Intelligence
Researchers William D. Hopkins, Jamie L. Russell, and Jennifer Schaeffer from Georgia State University and the Yerkes National Primate Research Center in Atlanta turned to chimpanzees. They administered the Primate Cognition Test Battery to 99 adult chimpanzees ranging in age from 9 to 54 for whom they also had genetic data and information on the relatedness among each individual.
The battery is comprised of thirteen tasks, which measure spatial cognition, numerical cognition, causality, and social cognition. The tasks are very straightforward. One of the tests for measuring spatial cognition, for example, involves a researcher hiding food in two of three cups. If the chimpanzee has good spatial memory, it should look for food in those two cups, rather than in the third, empty cup.
After combining the chimpanzees' performance on the IQ test with their genetic data, the researchers discovered that fifty percent of the variation in intelligence was due to genetic factors. When it came to specific environmental factors that the researchers considered, neither sex nor rearing history contributed significantly to the chimps' intelligence. That is, whether they were raised by humans or by their mothers did not significantly impact their intelligence once they became adults.
The researchers then broke the chimpanzees' performance down by skillset, and discovered that while all aspects of intelligence had some variation that could be attributed to genetics, variation in spatial and social communication skills were in particular influenced by their genes. (Variation in the chimps' understanding of causality reflected fairly little genetic influence.)
Impressively, the researchers managed to re-test 86 of the original 99 chimpanzees after some time had passed. Not only did the overall measure of intelligence heritability hold up the second time, but the individual tasks sorted in a nearly identical pattern, with performance on tasks related to spatial and social cognition dividing into two clusters. Both the structure and heritability of intelligence held up across two different assessments of the same group of chimps. In humans, intelligence is thought to remain fairly stable over time. The same appears to be true for chimpanzees as well.
A Useful Comparison
Hopkins, Russell, and Schaeffer write:
From an evolutionary standpoint, the results reported here suggest that genetic factors play a significant role in determining individual variation in cognitive abilities, particularly for spatial cognition and communication skills. Presumably, these attributes would have conferred advantages to some individuals, perhaps in terms of enhanced foraging skills or increased social skills, leading to increased opportunities for access to food or mating.
That isn't a particularly surprising or novel statement on its own. We already knew that genes have an important job when it comes to intelligence and cognition. But what's useful is that we can assume chimpanzee intelligence isn't influenced by factors like socioeconomic status, the quality of their school districts, or any of the dozens of other variables, both obvious and subtle, that influence human development. That means we can examine the "genetic" side of their intelligence more easily.
With a basic understanding of the proportion of cognition that can be attributed to genetics, researchers now have a place to start if they want to use the evolution of chimpanzee smarts as a comparison point for our own.
Header photo: Thomas Lersch/Wikimedia Commons