Brain size predicts problem-solving ability in mammalian carnivores

Abstract

Despite considerable interest in the forces shaping the relationship between brain size and cognitive abilities, it remains controversial whether larger-brained animals are, indeed, better problem-solvers. Recently, several comparative studies have revealed correlations between brain size and traits thought to require advanced cognitive abilities, such as innovation, behavioral flexibility, invasion success, and self-control. However, the general assumption that animals with larger brains have superior cognitive abilities has been heavily criticized, primarily because of the lack of experimental support for it. Here, we designed an experiment to inquire whether specific neuroanatomical or socioecological measures predict success at solving a novel technical problem among species in the mammalian order Carnivora. We presented puzzle boxes, baited with food and scaled to accommodate body size, to members of 39 carnivore species from nine families housed in multiple North American zoos. We found that species with larger brains relative to their body mass were more successful at opening the boxes. In a subset of species, we also used virtual brain endocasts to measure volumes of four gross brain regions and show that some of these regions improve model prediction of success at opening the boxes when included with total brain size and body mass. Socioecological variables, including measures of social complexity and manual dexterity, failed to predict success at opening the boxes. Our results, thus, fail to support the social brain hypothesis but provide important empirical support for the relationship between relative brain size and the ability to solve this novel technical problem.

Keywords: brain size; carnivore; intelligence; problem-solving; social complexity.

Fig. 1.

(A) We tested the performance of zoo-housed individuals in 39 species from nine carnivore families by exposing them to our puzzle box problem, with the box scaled to accommodate body size. (B) The relationship between body mass (kilograms) and brain volume (milliliters) in 39 mammalian carnivore species. (A) Species in gray and (B) family names in gray represent species in which no tested subjects opened the box. Note that, in B, two species in the family Felidae (Panthera pardus and Puma concolor) have overlapping points.

Fig. 2.

(A) Carnivore species with larger brain volumes for their body mass were better than others at opening the puzzle box. (B) There was no significant relationship between absolute brain volume and success at opening the puzzle box in carnivore species when body mass was excluded from the statistical model. Data presented represent the average proportion of puzzle box trials in which species were successful and are for presentation purposes only, whereas statistical results from our full model used for our inferences are shown in Table 2. Mass-corrected brain volume in A is from a general linear model and for presentation purposes only; statistical results from the full model are shown in Table 2.

Fig. 3.

(A) Individuals from carnivore species with larger brain volumes relative to their body mass were significantly better than others at opening the puzzle box (Table 2). (B) There was no significant relationship between absolute brain volume and success at opening the puzzle box in our individual-level analyses in which body mass was excluded (Table S2). Individuals with success equal to one opened the box, whereas those with success equal to zero did not. Mass-corrected brain volume in A is from a general linear model and for presentation purposes only; full statistical results are shown in Table 2 and Table S2. Regression lines represent predicted relationships from statistical models investigating the association between (A) brain volume relative to body mass or (B) log (brain volume) and success at opening the puzzle box.