A commentary on "intelligence"


Intelligence is a notoriously tricky phenomenon to reckon. One way to assess intelligence is perhaps in terms of how well an individual--or species--is able to upload and process information, contextualize it, store it, and then retrieve it in real time to aid planning, mapping, and other orientation. Humans are perhaps unique in the extent to which these processes are abstracted and interwoven with language.


People who have investigated the phenomenon of human intelligence have long recognized that there are many dimensions to it. It is instructive that, even within our own species (which we can access through shared language, shared sensibilities and lived experiences), it is quite difficult to nail down intelligence. Much less with other species. Bears and their kin don't speak a verbal language in any sense that we recognize it, and orient to the world in fundamentally different ways; for example, with a highly developed sense of smell.


All of that said, species with comparatively big brains tend to be "more intelligent." This follows from the simple fact that a big brain provides more space and related wet wiring for carrying out complex sensory functions and cognitive tasks. And it is has been pretty conclusively shown that this is best defined in a relative sense--as unit volume of brain per unit volume of body mass or some other measure of body size. These notions were probably best articulated in a book devoted to the topic written by Stephen Gould ("The Mismeasure of Man").


That said, the part of the brain that contributes proportionately the most to brain volume matters in any reckoning of "intelligence." Perhaps most relevant is the relative volume of the frontal cortex and, of that, the neocortex. These areas of the brain are the most closely associated with spatial reasoning and conscious thought, including the deployment of abstractions.


However, we are not relegated to looking exclusively at volumes of brain structures to estimate intelligence; there are many more direct ways that involve observing animals and testing them under controlled situations to determine how fascilely they employ abstractions, how quickly they learn, and how able they are to extrapolate and otherwise deploy new knowledge.


In what follows I cover all of these indicators of intelligence, starting with total brain volume, then looking at proportional volume of different brain structures, and concluding with the results of several studies that more directly investigated the intelligence of bears. All of this is necessarily comparative--that is, in comparison to other species or taxa.


The figure to the left summarizes the results of two studies that show bears (of the family Ursidae) to have comparatively the largest brains of any carnivores. Relative brain mass (or volume) is reckoned in two different ways: relative to body mass and relative to either skull or body length. Body mass is perhaps the more informative basis for comparison, with the proviso that body mass of bears is fattier than that of most other species. Which begs the question: How does adipose tissue (which is largely inert and without enervation) relate to brain function? This is an open question, which is why it is worth looking at brain volume relative to both skull and body size.


The right-hand graph shows that bears have the largest positive deviation of any carnivore family in brain size relative to both body and skull size. A similar result is shown to the left in terms of the inset bars scaled to "relative endocranial volume" (shown at the bottom). Note, too, that the results farthest left are shown relative to the evolutionary (phylogenetic) relations of various species.


One additional note here: Despite all of the debate that has transpired during the last 30 years over how to statistically reckoned relative brain size, Swanson and company end up with the same conclusion in 2012 as John Gittleman reached in 1986. 

The relationships in the two figures above amplify on the basic notion that bears are relatively "big-brained." In Panel A brain volume is related to skull length; in Panel B, to body mass. Each dot represents the average for a given carnivore species, with bear species denoted by the larger brown dots, and individual bear species by four-letter acronyms. Bears stake out the extremes of large size for these relationships, which means that there aren't members of other taxa in the same size range to provide a more definitive contrast. For this reason the statistically fitted relationships are shown based on all species, including bears (gray dashed line), as well as based on non-bear species alone, with this relationship extrapolated into the size range of the bears (solid black line). 


The relationship extrapolated from other species is consistent with the big-brain status of bears. Of the bears, the sun bear (Urmal, Ursus malayanus) and Asiatic black bear (Urth, U. thibetanus) have relatively the largest brains, perhaps along with the polar bear (Urmar, U. maritimus). The other bear species tend to fall along or closer to the main trend line, meaning they don't exhibit any major deviations that would indicate greater or lesser brain function (intelligence?) than one might expect by their size. One might conclude from this that bear species of the Southeast Asian lineage (Urth, Urmal, and Urur) tend to be "smarter." Another conclusion might be that the remaining bear species are not any more intelligent than size alone dictates. But, next, let's consider the relative size of different brain structures, especially those more overtly identified with intelligence.

The relationships above come from two different studies that included bears in their investigations of brain structures as a part of total brain volume--one published by Romain Willemet (right) and the other (left) by Swanson and colleagues (both in 2012). Both sets of results focus on carnivores.


Panel A, to the left, shows the proportional size of the frontal cortex (that is, volume of the frontal cortex relative to total brain volume); panel B shows the same for the combined volume of the cerebellum and brain stem. The dashed gray line extrapolates a relationship developed for carnivores other than bears, whereas the solid black line includes bears (for the same reasons given immediately above). The frontal cortex is closely associated with higher-order functions such as spatial reasoning and conscious thought, whereas the cerebellum and brainstem are more closely associated with less overtly cognitive functions--including regulation and coordination of movement, posture, and balance. These results are consistent with the notion that bears (the beige squares) are comparatively intelligent in the ways that we would recognize it, primarily through relative enlargement of the frontal cortex. On the other hand, the size of brain elements governing more basic functions are not any larger than one might expect by the size of the brain--hence, for example, we would not expect them to be exceptionally agile.


The results to the right express size of different brain components in somewhat more abstract terms employing latent variables (principal components, or PC) that distill main themes among--in this case--size of brain organs. As it turns out, the main dimension of variation in carnivore brains (PC I) is organized almost wholly around enlargement of the neocortex (that is, the brain bit associated with higher order cerebral function). Similarly, the next-most important dimension (PCII) is organized primarily around enlargement of the cerebellum. So...emphasizing the same features as in graphs A and B to the left. The size of the circles denoting individual species is proportional to overall brain size relative to body size. Here, the sole respresentative of the bear lineage (polar bears, U. maritimus) would again suggest that, second only to marine mammals such as seals and walruses, bears are among the brainiest of carnivores. These results would also suggest that at least polar bears have a comparatively enlarged cerebellum.

An aside on sociality and brain size


Perhaps one of the more hotly contested topics among those investigating brain size (and intelligence) relates to evolutionary drivers. There is a veritable cottage industry that has built up around either promoting or contesting the degree to which sociality is a major driver, with the primary bone of contention being whether more highly-social group-living species have brains that are comparatively larger than those of solitary species--which includes the bears. Perhaps the most reasonable (as well as plausible) reconciliation of the two contested positions has been the argument that it is not sociality as much as it is "culture" that has driven encephalization (that is, relative enlargement of the brain). In other words, the more that a species depends upon sharing and transmitting knowledge for survival, the greater the encephalization. This conceptualization would accommodate the large-brained bears, which clearly accumulate and convey knowledge, primarily through the mother-cub relationship.


My own investigations of relations between sociality and encephalization suggest that, when looking at all mammals, the contrasts between solitary and group-living (or more social) species diminish as body size increases. In other words, there is a trend towards larger brains among smaller social versus solitary species, and little or no difference among the largest species. When the scope is limited to land-dwelling carnivores, there is little or no difference at any body mass. Moreover, the solitary bears emerge (again) as the biggest-brained of all. 

Brain growth & development


One final topic related to brain size, as such, is the rate of brain growth along with associated factors.


The graphs to the left show, in A, the size of a newborn's brain relative to the size of its mother's brain; in B, the gain in brain mass during growth, again relative to maternal brain size; in C, the length of the juvenile period relative to size of the mother's brain; and, finally, in D, the duration of lactation in relation to total duration of juvenility. Each dot denotes a different mammals species, with bears highlighted in beige.


Taken together, these results show (or suggest) several interesting phenomena. First, consistent with exceptionally small overall size of cubs at birth (see  Body size), cubs also have relatively the smallest brains. They, then, accumulate the greatest brain mass of any species during their juvenile period. But...they do this without the benefit of an exceptionally long juvenile period or long-drawn-out nursing. In short, cubs need to build a lot of brain matter at a high rate, which implies that they need an exceptionally rich diet during their formative months (see Nutrition).  

Direct reckonings of intelligence

Several people have devoted their lives--or a significant portion of their lives--to observing bears with the intent of deep learning about how they orient to the world. Some of these inquiries have been more overtly observational, emphasizing, here, that I consider close observation to be an important source of insight. One of the first was Peter Krott and his wife, Gerturde, who adopted, raised, and observed brown bear cubs in the Italian Alps during the 1950s. This tradition has been continued by the likes of Charlie Russell, who likewise raised and closely observed brown bears cubs in Kamchatka. Other researchers have been more systematic, but no less closely attentive, including Lynn Rogers (with black bears in Minnesota) and Barrie Gilbert and Stephen Stringham, both with brown and black bears in Alaska. In addition to these close observers of bears in the Wild (or semi-Wild), several researchers have undertaken investigations of bears in more controlled settings. A pioneer in this regard--Ellis Bacon--worked with black bears during the 1970s. After a relatively long hiatus, another researcher--Jennifer Vonk--has enthusiastically taken up the torch, producing a number of papers in recent years reporting on the results of investigations into the cognitive abilities of bears. Interestingly, another source of insight into the nature of bear-intelligence has come from investigations of giant pandas, which seems a little odd given how comparatively few survive either in the wild or in zoos.


So, some results of these investigations are: Bears are known to use tools, which puts them in the same league as chimps. They can also count. They have the ability to learn, develop, and deploy abstract categorizations similar to the abilities of primates, which suggests a relatively well-developed ability to formulate concepts. However, they (or at least pandas) don't recognize themselves in mirrors. Rather, they see their self-image as another individual of their species; which is differs from the ability of other intelligent but more social animals (gorillas, elephants, dolphins) to identify themselves in such mirror-based tests.


Most of the researchers involved in this work are skeptical about the "social-intelligence" hypothesis (see above). From their perspective, most facets of bear intelligence relate back to the demands placed on an omnivore in a complex dynamic world, coupled with the need to find, extract, manipulate, and process foods at finer scales. They see bears as being comparable in most facets of intelligence to primates, and this despite the fact that bears are primarily solitary (which, as a side note, is not the same as asocial). 


Laboratory-based results aside: most of those who have worked extensively with bears would probably describe these animals as "intelligent." This based on their apparent problem-solving ability, extensive geo-(and temporal) referencing of food sources, and related abilities to discern and differentiate elements of the environment at a very fine grain.


One striking example of this latter phenomenon is evident in how difficult it is to "aversively condition" so-called problem bears. The aversive conditioning enterprise aims to teach bears that have been involved in conflicts with people to avoid certain problematic situations through the administration of closely associated unpleasant experiences; for example, beating them with rubber bullets, harassing them with dogs, or subjecting them to loud noises. Aversive conditioning often fails, not because bears can't learn, but because they often learn too well. For example, some bears learn to avoid the people delivering the unpleasant experiences, and still access the foods that brought them near people in the first place. This involves the apparent ability on their part to recognize specific vehicles, people, and predictive circumstances. In other words, these bears deploy a system of categories and distinctions that allow them to orient to people and situations at a fine grain, which means that the involved bears don't generalize their unpleasant experiences to an overly broad category of situations. Aversive conditioning can fail for other reasons, but the "intelligence" of bears on the receiving end is clearly a complicating factor.