Image of two hyena cubs. Photo courtesy of Jennifer Smith.

A socially complex world


Hyena cubs Normandy and Iwo Jima. Photo by Kate Shaw.The role of dominance in the spotted hyena society is complex and ever-changing as new cubs are born and the dynamics of the clan change.

Aside from the reversed gender roles and unusual  physiology which makes spotted hyenas unique, their highly complex societies represent another area of interest to scientists.

Professor Kay Holekamp's team is using the spotted hyena as a model animal in which to try to understand why big brains and great intelligence evolved.

Scientists have two main theories to explain why humans and other primates have relatively large brains and great intelligence. Human brains are several times larger than some would predict based on needs imposed by metabolism and movement alone, and this has intrigued scientists as to why humans have evolved this way. One theory suggests that intelligence has been favored in species forced to cope with major challenges in their physical environment, such as the need to navigate through a three-dimensional world or the need to develop tools to extract well-protected foods. The second explanation is the social complexity hypothesis, which suggests great intelligence gives animals a big advantage when they live in complex social groups. While both hypotheses have received support in the scientific community, the strongest evidence favors the social complexity hypothesis.

The social complexity hypothesis suggests that the primary force in the development of the brain was the need to anticipate, respond to and manipulate the social behavior of other group members. The theory suggests that large brains reflect the computational demands of complex social systems. In other words, the demands of social living are the main reason for the evolution of intelligence. The frontal cortex of the brain is heavily associated with social decision-making, and the social complexity hypothesis suggests the demands of society have led to the evolution of the large frontal cortex in the human brain. Most research in the 20th century focused on primates, however, other scientists are testing this theory with social animals ranging form birds to spotted hyenas.

The social complexity hypothesis predicts that mammals living in large, intricate societies should exhibit enhanced abilities in social cognition similar to those found in humans and other primates. Evidence for this may be seen in the expansion of the frontal cortex in the brain.

Because spotted hyena societies are large and complex, they offer a good model in which to test the social complexity hypothesis.

Holekamp and her colleagues and students are testing the social complexity hypothesis in two different ways. One way is to examine the size of the brain of spotted hyenas, focusing especially on frontal cortex. The difficulty with this research is that measuring a spotted hyena brain requires obtaining a hyena skull that is in a condition good enough to be measured. These skulls are difficult to find, so collecting enough data to provide solid research is nearly impossible. However, Dr. Sharleen Sakai in the Psychology Department at MSU has developed a very clever way to reconstruct a "virtual brain" from a spotted hyena skull using computer tomography (CT) scans.

Another way of testing this theory is by testing hyena intelligence directly. Although hyenas can understand their social hierarchy, a different set of cognitive skills may be needed for non-social intelligence. Tests of both social and non-social intelligence are currently being planned in the Holekamp Lab for implementation in 2008 and 2009. The researchers will test the intelligence of spotted hyenas by using various types of intelligence tests.

For example, scientists will place food inside a box which requires the hyena to figure out how to open the door. These simple tests will be used to gauge the level of intelligence among spotted hyenas, and assess their learning ability. 

The spotted hyena is a strange and unique animal which helps answer many scientific questions while simultaneously generating many new and unanswered questions to scientists. In Africa, spotted hyenas are the second largest carnivore after lions, and they are more abundant than any other large carnivore on the continent. Their endurance and strength make them successful hunters and their presence is an indicator of a healthy ecosystem. These animals are providing scientists rich data in many areas ranging from health and hormones to complexities of societal relationships.