Chimps stick grass in their ears to be cool: notes on cultural transmission

grass in ear

1. In 2010, a female chimpanzee named Julie began repeatedly stuffing a stiff blade of grass into her ear. This Grass-in-ear behavior has affectionately been dubbed “GIEB” by the scientists who observed it.

2. Out of a group of twelve chimpanzees, eight engaged in GIEB. In three other groups of chimpanzees found in other locations in the same forest, only one was ever seen to GIEB.

3. The more that an individual associated with Julie, the more likely they were to GIEB.

4. After the inventor of GIEB died – if one could be said to invent a thing like putting grass in one’s ear – two chimpanzees continued to engage in the activity. They were never seen to do it together, let alone put grass in the other one’s ear.

5. A young monkey named Imo once noticed that her sweet potatoes were covered in sand and that if she dunked them in the water they would become clean. Within a few years, every monkey on her island was dunking sweet potatoes. She later learned that if she dunked them in the ocean instead, plunging them in after every bite, they would taste even better. The lesson? Monkeys love seasoned potatoes.

Japanese macaque stone handling

6. Some Japanese macaques like to play with stones, clicking and clacking them, rolling them along their hands, cuddling or pushing or throwing them. This was first invented by a young female monkey named Glance in 1979. Her playmates learned it first, followed by theirs. What began as transmission among friends has transformed into transmission among generations: now babies learn it from their mothers.

7. There are at least 11 mutations of this stone handling behavior, including “Rub With Hands”, “Grasp Walk”, and “Flinting”. These variations appear to be transmitted between tribes of monkeys when males migrate from one to another. Additionally, each generation appears to add complexity as each individual inadvertently contributes some new idea.

8. Monkeys are not the only animals with social transmission of ideas; many other animals do, though it may not necessarily be for the best. When young guppies are learning where to eat, they follow an older fellow to a source of food. Slowly, they learn from the older guppy which route to take to their food. As time goes on, one guppy learns from another and a route is set. However, this can be maladaptive when there is a faster route available: follow the group even if they know there is a quicker way.

9. One can digitize animals and ask how their theoretical equivalents toss around cultural traits. What causes these electronic cultures to die out? Simple: small groups, high mortality, poor transmission, and costly traits. Prestigious traits, or traits with group consensus, die out just as quickly as any other. In other words, a culture held in high esteem is just as mortal as any other.

10. The connections between members of a group aren’t uniformly random. Instead, they tend to form small worlds, where any two members are just a few steps away from each other. Thank you, Kevin Bacon. In any random network, as the set of connections reaches half the number of members, a “percolation” process causes many small groups to begin congealing into one large group. Much can be learned about sociality and culture using these ideas.

11. It is possible to classify social learning mechanisms in ten distinct ways: stimulus enhancement, local enhancement, observational conditioning, social enhancement of food preferences, response facilitation, social facilitation, contextual imitation, production imitation, observational response-stimulus learning, and emulation.

12. A computer tournament revealed that even indiscriminate copying is often better than trial and error learning. Copied individuals will often perform the best available behavior, and the better the behavior the more likely they were to survive. Thus, survival itself made behavior a non-random sample of the best behavior. Individuals were themselves highly useful filters of information waiting to be copied.


Huffman, M., Nahallage, C., & Leca, J. (2008). Cultured Monkeys: Social Learning Cast in Stones Current Directions in Psychological Science, 17 (6), 410-414 DOI: 10.1111/j.1467-8721.2008.00616.x

van Leeuwen, E., Cronin, K., & Haun, D. (2014). A group-specific arbitrary tradition in chimpanzees (Pan troglodytes) Animal Cognition DOI: 10.1007/s10071-014-0766-8

Laland, K., & Williams, K. (1998). Social transmission of maladaptive information in the guppy Behavioral Ecology, 9 (5), 493-499 DOI: 10.1093/beheco/9.5.493

Nunn, C., Thrall, P., Bartz, K., Dasgupta, T., & Boesch, C. (2009). Do transmission mechanisms or social systems drive cultural dynamics in socially structured populations? Animal Behaviour, 77 (6), 1515-1524 DOI: 10.1016/j.anbehav.2009.02.023

Stocker R, Green DG, & Newth D (2001). Consensus and cohesion in simulated social networks Journal of Artificial Societies and Social Simulation, 4 (4)

Rendell L, Fogarty L, Hoppitt WJ, Morgan TJ, Webster MM, & Laland KN (2011). Cognitive culture: theoretical and empirical insights into social learning strategies. Trends in cognitive sciences, 15 (2), 68-76 PMID: 21215677


Friends with benefits

tl;dr: Rodents will help each other get out of trouble, though they will help each other more if they are related. Social learning in rodents can require information transmission between ACC and amygdala, and the strength of synapses in mPFC dictates social status.

He wanders into the room and stops – someone else is peering at him out of a tiny plastic cage. Wandering over he must decide: should he help him out of the cage? Or let the creepy situation remain creepy, and leave them stuck in there?

Rats, it turns out, aren’t big fans of creepy situations and will actively go out of their way to help their furry compatriots escape from their cages. Not only will they help other rats escape their cages – even if they don’t know them – but if they find a bite of chocolate they’ll hand over some of that as well. [Though if you look at the data: the little bastards wait half a week before they get around to doing it.]

Screen shot 2014-02-08 at 11.27.27 AM

That’s fine but things can get a bit sinister when the rats aren’t just strangers but strangers that appear different. When they find another rat trapped in a cage that is of a different strain, the free rats would rarely attempt to let the trapped rats loose. This isn’t purely a matter of rats being different from one another, but rather of rat-features that they weren’t familiar with. When rats were housed with rats of different strains, they would help other rats of that strain out. Individuals of that outgroup had been ‘humanized’, so to speak. Yet, own-group preference wasn’t innate – if they weren’t housed with other rats of their own strain, they wouldn’t help them, either. For an example, watch this movie from the paper (which I can’t directly embed).

We already know a bit about the neuroscience of empathy and social structure in rodents. A mouse that observes a fellow mouse receiving painful shocks in a certain area of their cage will learn to avoid that area through pure social observation. However, they learn better when it is a sibling that is being shocked than when it is an unrelated rat. This learning requires a region of the brain known as the anterior cingulate cortex (ACC), though the region can be inactivated during later retrieval and recall without affecting the behavior. It also requires the amygdala, not just for learning but also for later retrieval and recall. During learning, the ACC and amygdala are connected by strong (theta) rhythms, potentially to transmit information between the areas.

Screen shot 2014-02-20 at 10.58.38 AMAnother factor guiding social behavior is social status. Status affects behavior on a range of levels, from how decisions are made to how healthy an individual is. It is pretty surprising to me that in rodents, social status can be directly changed by changing the strength of synapses in the medial prefrontal cortex (mPFC). I’ve only ever seen a broad neuromodulator like serotonin do something like that, though I would hesitate before suggesting that they two mechanisms were connected. On the other hand, mPFC is upstream of serotonergic areas so increased synaptic strength could mean increased serotonin!

Ben-Ami Bartal I, Rodgers DA, Bernardez Sarria MS, Decety J, & Mason P (2014). Pro-social behavior in rats is modulated by social experience. eLife, 3 PMID: 24424411

Ben-Ami Bartal I, Decety J, & Mason P (2011). Empathy and pro-social behavior in rats. Science (New York, N.Y.), 334 (6061), 1427-30 PMID: 22158823

Wang F, Zhu J, Zhu H, Zhang Q, Lin Z, & Hu H (2011). Bidirectional control of social hierarchy by synaptic efficacy in medial prefrontal cortex. Science (New York, N.Y.), 334 (6056), 693-7 PMID: 21960531

Jeon D, Kim S, Chetana M, Jo D, Ruley HE, Lin SY, Rabah D, Kinet JP, & Shin HS (2010). Observational fear learning involves affective pain system and Cav1.2 Ca2+ channels in ACC. Nature neuroscience, 13 (4), 482-8 PMID: 20190743

Learning socially but not socially learning

How do we distinguish learning from our friends from learning because our friends happen to be around? When I was younger, Goldeneye on the Nintendo 64 was the game to play, but I was sadly N64-less. Did I learn how to play Goldeneye because my friends were good at it and showed me, or because whenever I was around them, Goldeneye was available for me to play? But here’s a fact: I suck at Goldeneye. If I learned anything from my friends vis-a-vis Goldeneye, it was how to be humble in the face of continual defeat.

When animals are foraging for food, they face a similar problem. If they forage on their own, they don’t lose any of their reward (like their self-respect) to other animals. But by foraging socially they are able to increase the likelihood that they will find some food.

One of the biggest problems that social foraging can solve is that of risk-aversion: the preference for guaranteed rewards over risky ones, even when risky ones will be more rewarding over the long-run. In many cases, this preference is a simple reflection of the learning that all animals undergo. Risky rewards have both very large and very small rewards. When given the choice between multiple options, a string of bad luck on the risky option will lead an animal that learns to give up that choice and stick with the less risky option.

Yet learning dynamics are slightly different when an animal is surrounded by other animals. Animals are not identical clones of each other (usually) but have a variety of personal preferences for risk and reward. If you plop sparrows in front of both more and less risky options, of course they’ll generally prefer the risky options. But sparrows come in groups! And when in groups, they can be scroungers, hanging back and waiting to see what others are doing. And this lets them take advantage both of the range of group preferences as well as the range of learning in the group.

Interestingly, individuals only learn about the desirability of an option when they were the ones to have chosen the option but not when they watched (and joined) another individual making a choice. I’m not sure if there is a lesson here on group learning? Perhaps it is better for the group to keep their knowledge uncorrelated so that it is combined their knowledge will be as diverse as possible? But either way, they are not socially learning, not learning how to do something by watching another animal. Rather, they are learning by being in a social group that allows them to take advantage of the learning of each individual in the group.


Ilan T., Katsnelson E., Motro U., Feldman M.W. & Lotem A. (2013). The role of beginner’s luck in learning to prefer risky patches by socially foraging house sparrows, Behavioral Ecology, 24 (6) 1398-1406. DOI:

Humans are not the only copycats…

Both sets of newcomers seemed to follow social cues when selecting their snacks. Baby monkeys ate the same colour maize as their mothers. Seven of the ten males that migrated from one colour culture to another adopted the local colour preference the first time that they ate any maize. The trend was even stronger when they first fed with no higher-ranking monkey around, with nine of the ten males choosing the locally preferred variety. The only immigrant to buck this trend was a monkey who assumed the top rank in his new group as soon as he got there — and he may not have given a fig what anyone else ate.


“The take-home message is that social learning — learning from others rather than through individual trial and error — is a more potent force in shaping wild animals’ behaviour than has been recognized so far,” says Andrew Whiten, an evolutionary and developmental psychologist at St Andrews and co-author of the paper.

Humans are not the only copycats.  (More from Ed Yong).  With the key question being: what are the neural mechanisms that distinguish between social learning and ___ learning?

Posts this week

Type of species and type of social network determine how parasites infect a population as it gets larger

Hermit crab social networks!

Social needs sculpt primate faces

Remember: song learning is social learning

Social decision-making across species …and more, but older

Economic Sociology newsletter on New Institutional Economics

A bit late on this one but genoeconomics is an important trend

A really great writeup about serotonin and anorexia

Elephant seal foraging!

When grasshoppers are afraid of spiders, plants decay more slowly.  This is the whole point of this blog: the environment and our interactions with our environment shapes our bodies (and minds!), and the two really cannot be disentangled.