Hey, it's Lily again. I'm a graduate student out in the field right now collecting cognitive data with the hyenas. One of the cognitive tasks I’m giving hyenas tests self-control, which is also known as “inhibitory control” in many scientific studies. Inhibitory control is the ability to resist a prepotent motor impulse in circumstances that demand restraint. In humans, the “marshmallow test” is a famous self-control test given to small kids. Children are presented with a marshmallow and told that if they can wait fifteen minutes without eating the marshmallow they’ll be rewarded with a second marshmallow. Inhibiting the impulse to eat the marshmallow right in front of them is extremely difficult for many kids and how well kids do on this task is highly predictive of success in life as adults.
|The Marshmallow Test|
Inhibitory control is important for other cognitive abilities because it’s thought to be a precursor to more complex thought. Before thinking about how to solve a problem, one must be able to take a step back to assess a situation, i.e. “stop and think”.
I’m testing inhibitory control in spotted hyenas using a tube task. It’s a standard task for testing inhibitory control in animals and is part of a family of “detour tasks”. Detour tasks test inhibitory control by requiring an animal to initially move away from a food reward before moving towards it to retrieve it.
This is often done by placing a barrier, like a fence, in front of a clearly visible food reward. In order to get the food, the animal must walk around through a gap in the fence, which requires moving away from the desired food reward. This can be really difficult for many animals who want to run straight towards the food!
|A juvenile spotted hyena interacting with the tube task.|
The tube task uses a transparent cylinder the rests horizontally on the ground with both ends open. The animal is presented with the tube and they must reach inside either end of the tube without bumping into the side of the tube. Prior to test trials with the clear tube, they are given familiarization trials with a solid tube so that they learn where the openings on the tube are.
|An adult female approaches the familiarization tube.|
Spotted hyenas are so proving themselves to be quite good at this task, but they occasionally have lapses in their self-control!
SRG fails the tube task.
SRG passes the tube task.
In animals, inhibitory control is related to brain size, dietary breadth, and the degree of fission fusion dynamics. (MacLean et al. 2014; Amici et al. 2008). Amy Fontaine wrote about fission fusion dynamics (FFD) in an earlier blog post here. Animal societies with a high degree of FFD are those like chimpanzee society. Individuals live in large social groups, but most of the time the entire social group does not live together. Instead, they break up into small subgroups of just a few animals and only come together in large groups for specific events. This means that individuals in a social group sometimes go days, weeks, or even months, without seeing some of their group mates. This kind of social living is thought to be cognitively challenging because individuals must remember the identities and social ranks of all their group mates even though they don’t see them that often.
For hyenas, living in a high FFD society is adaptive because it means they can split up to look for food but join together when they need to fight off lions or other hyena clans to defend their territory (Smith et al. 2008).
|Hyenas from Happy Zebra Clan go on a border patrol.|
Observing hyenas in the field it’s easy to see that they have great inhibitory control. I’ve seen hyenas patiently wait for hours around a mother giraffe who’d had a still-born calf. They all had the inhibitory control to not mess with the mom, an adult giraffe has a very powerful kick, and instead went to sleep about 30m away from her to wait for her to abandon the still-born calf. In addition, hyenas will wait patiently around a carcass that lions have control of. An adult male lion can kill a hyena with a single swipe of the paw and hyenas have to have the inhibitory control to know just when they can go in and steal food without getting hurt. Out in the Mara, a hyena without inhibitory control will get killed!
|A hyena waits for a mother giraffe to leave the still born calf at her feet.|
In addition, spotted hyenas require a lot of inhibitory control in the social domain. Lower ranking hyenas have to inhibit all aggression towards higher rankers, especially when food is present. I’m especially interested in inhibitory control in male hyenas. When hyenas are born, they obtain a social rank directly below their mothers in the hierarchy. Some male hyenas are born as high rankers and some are born as low rankers. However, when male hyenas hit sexual maturity they leave to join a new clan in search of mating opportunities. When a male hyena joins a new clan, he joins at the very bottom of the hierarchy. In their new clans, male hyenas must possess an extraordinary degree of inhibitory control and inhibit all aggression around their new clan mates. Because male hyenas are “destined” to become extremely low ranking when they’re adults and clearly learn to inhibit all social aggression around females and other hyenas in their new clans I think they’ll have much better self-control on the tube task.
|A male hyena shows submission by going ears back to an aggressive female.|
The interesting part is, I will also be able to test a prediction of the social brain hypothesis. The social brain hypothesis predicts that big brains are a result of the cognitive demands of living in complex social groups. So far, the social brain hypothesis makes strong predictions in primates and complex sociality does predict complex social cognitive skills, but it’s unclear if social pressures select for cognitive skills outside the social realm. I.e. it’s not clear that complex sociality predicts things like tool-use or spatial navigation. So, just because male hyenas have great inhibitory control in the social realm, it’s not totally clear that they will have great inhibitory control on a physical task like the tube task. If they do, it means that social inhibitory control also makes male hyenas better at physical inhibitory control!
|A hyena plays with the opaque tube.|
Amici, F., Aureli, F. & Call, J., 2008. Fission-fusion dynamics, behavioral flexibility, and inhibitory control in primates. Current biology : CB, 18(18), pp.1415–9.
MacLean, E.L. et al., 2014. The evolution of self-control. Proceedings of the National Academy of Sciences of the United States of America, 111(20), pp.E2140–8.
Smith, J.E. et al., 2008. Social and ecological determinants of fission–fusion dynamics in the spotted hyaena. Animal Behaviour, 76(3), pp.619–636.