The question of primate intelligence
Primates have bigger brains than most other mammals given their body size. What evolutionary pressures selected for increasing brain size and cognitive abilities? Was it the challenge of finding scarce, patchy fruit in a forest? Or competing with other members of the social group for resources? Or an interaction of ecological and social factors? What role does the enhancement of sensory systems play? Are basic principles of non-human and human learning shared as the result of our evolutionary history?
Elena Cunningham and her collaborators have looked at the travel and movement choices of primates to preferred foods to gain insights to these questions. Elena’s current research focuses on the cognitive abilities of lemurs.
Fig. 1. Lemur catta, Varecia variegata, Eulemur collaris, Eulemur mongoz, Varecia rubra
Lemurs are considered the best living example of the primitive primate mind (Fichtel and Kappeler 2010). They split from the common ancestor of monkeys, apes, and humans about 60 mya (Yoder et al. 1996). Compared to monkeys and apes, they tend to have smaller brains, a less well-developed visual system, and a more highly developed olfactory system. Understanding lemur cognition is an essential part of understanding the evolution of cognition in the primate order.
Current research projects
Ruffed lemurs (Varecia) in Ranomafana National Park, Madagascar: Learning from their mistakes
In nature, lemurs are found only on the island of Madagascar, which is known for its harsh and unpredictable climate. Because of the climate, there is less fruit on Madagascar than other places where primates live. Fruit is more important to the diet of black and white ruffed lemurs (Varecia variegata) than any other living lemur. Analysis of the ruffed lemurs travel paths with computer programs indicates that lemurs did remember trees with abundant fruit and tree cisterns. They returned to these locations day after day from far away, and from different directions. Although about 60 % of the ruffed lemurs daily path was spent searching for food, they learned from their mistakes: they were twice as likely to have a feeding bout in an area that they had visited in the previous three days and their feeding bouts were twice as long in places they had previously been.
- Collaborator: Charles Janson
- Student: Lyle Schofield
Fig. 2. Ruffed lemur at a tree cistern and feeding on fruit.
Long-term memory in Eulemurs: the importance of learning schedules
Primates in nature live in the same areas for years, or for their entire lifetimes. Long term memory lasting months or years would offer great selective advantage. It’s very hard to determine how long primates can remember important locations in the wild, so Elena conducted a series of experiments at the Lemur Conservation Foundation in Florida. The experiments showed that with a spaced learning schedule (the same that is effective for human learning), lemurs were able to remember the locations of containers with cantaloupe for two weeks. The pattern of their movements and choices indicates that they used memory and olfaction to visit and select containers.
- Collaborator: Malvin Janal
- Students: Maria Gonzalez, Rachelle Wolk
Fig. 3. Mongoz lemur eating cantaloupe hidden in take-out container and two lemurs at container.
The ability of ring-tailed lemurs (Lemur catta) to follow odor plumes to distant resources.
The ability of primates to use airborne odor cues to locate distant resources has not been previously recognized. Elena and her collaborators hid cantaloupe in the underbrush of a 10-acre forest, 4-17 m from a path used by the lemurs. The ring-tailed lemurs were able to detect the odor of distant fruit among the complex odors of a forest and use those olfactory cues to locate its source. Although sites were not baited after the group fed there, the lemurs returned to every site where they had fed, sometimes while they were actively searching for cantaloupe. This behavior suggests that individuals merged memories of past feeding events with immediate olfactory information.
- Collaborators: Devin Edmonds, Malvin Janal, Laura Stalter
- Student: Matthew Wilkens
Fig. 4. The study group on the habitual path.
Movie 1. After the group stops moving along the habitual path, two individuals go to a site on the right side of the screen. There are no containers at that site, which was baited 30 days prior. Other individuals go to the left side of the screen, pausing to sample the air before locating the bait.
Capture and Release
Elena has a long-term interest in reducing the risk of capture and release for primates in natural habitats. To this end, she and her collaborators have conducted two surveys, organized three round tables at international conferences, and published two peer-reviewed articles. She is Co-chair of the International Primatological Society Ad-hoc Committee to Address Issues Concerning the Capture and Release of Wild Primates
- Collaborators: Tatyana Humle, Annette Klein, Jo Setchell, Steve Unwin
Fig. 5. Data is collected from a darted Varecia prior to release, Ranomafana National Park, Madagascar.