Animals With Larger Relative Brain Sizes Are Better Problem Solvers

Animals with larger brains relative to their body size are the most intelligent, according to a new study. Kachalkina Veronika/Shutterstock

It may sound like an obvious thing to say, but a new study has found evidence that animals with larger brains relative to their body size perform better at problem-solving tasks.

While a link between intelligence and brain size has been speculated upon for some time, a lack of experimental evidence for this correlation has led to a considerable amount of debate and controversy. For example, some have claimed that while larger brains allow for enhanced memory storage, they do not necessarily lead to improved intelligence.

Publishing their findings in the Proceedings of the National Academy of Sciences, the researchers hoped to contribute to this dispute by engaging with several of the key theories and hypotheses that have been put forward as possible markers of cognitive capacity. For instance, aside from examining whether both absolute and relative brain size could be used to predict animals’ success at completing the task, they also set out to test the so-called social brain hypothesis.

This concept holds that superior intelligence evolved mainly in social animals, in order to facilitate the accomplishment of social tasks such as responding to and engaging with other members of their group. Should this be the case, one might expect social animals to outperform solitary animals when faced with a problem-solving task.

To test this, the researchers created a closed metal box containing food, which animals were then challenged to try and open by sliding a bolt latch. A total of 140 animals from 39 different species of mammalian carnivore were subjected to the test, with the size of the box adapted to accommodate each species. Among the species involved in the study were the likes of polar bears, tigers, and wolverines.

The bait inside the box was also carefully selected to ensure it would appeal to each participant. For instance, red pandas were given bamboo, while snow leopards were presented with steak. All animals were recruited from zoos in the U.S. and some of their attempts to open the box can be seen in the video below.




Results showed that “brain size relative to body mass was a significant predictor of success with [the] puzzle box,” with bears proving the most competent at completing the challenge. However, while the bears were among the largest animals involved in the study, the researchers also note that, on the whole, smaller species tended to perform better than larger ones. As such, the study appears to indicate that absolute brain size is a much less reliable predictor of intelligence than relative brain size.

Furthermore, the authors describe how “carnivore species living in social groups performed no better on our novel technical problem than solitary species.” They therefore state that, while greater social complexity may lead to evolutionary traits that allow for success at performing tasks in the social domain, it cannot be associated with enhanced ability to solve novel technical problems.

Although more research is needed to fully decipher the evolutionary traits which select for intelligence across all species, the study authors believe their work represents an “important step” in this direction.

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