Barbara J. King

Friday Animal Blog

What do Wild Vervet Monkeys Learn by Living near Humans?

January 14, 2011

Close encounters with vervet monkeys are a staple experience of tourists who stay at the grand lodges in African nature parks. These small, handsome green monkeys have a habit of darting up to poolside-dining tables and thieving food.

When I was monkey-watching in Kenya, my own experience in this regard was limited (after all, NSF tends not to fund leisure hours for dissertation work). While observing baboons in the bush, though, I would frequently see vervet groups passing by.

I was quite interested then to find a new study that asks whether contact with humans in the wild—not on the grounds of lodges—affects vervets’ acquisition of technical skills. The article became available online last week at the journal Folia primatologica. Written by Erica van de Waal and Redouan Bshary, it is called Contact with Human Facilities Appears to Enhance Technical Skills in Wild Vervet Monkeys.

Van de Waal and Bshary review studies that have used the now-popular “artificial fruit experiment.”Boxes containing food are given to monkeys or apes, with different ways of opening the box made available; the primates’ responses to the challenge are recorded. Rarely before this new study had the artificial-fruit approach been used on fully wild primates, and the hypothesis at issue here is new as well: Does exposure to human facilities affect the monkeys’ technical skill at the artificial-fruit-opening problem?

The research was undertaken at the Loskop Dam Nature Reserve in South Africa on six neighbouring groups of vervet monkeys, all habituated to humans. The groups, organized in matrilines (groups of related females) with multiple males, as is typical for the species, ranged in size from 13-23. Two of the 6 groups “were in regular contact with humans and their facilities.” That is, monkeys in both groups frequented areas with barbecue places, toilets, and dustbins; one of the groups also ranged through 3 fishermen’s huts. On weekends and holidays, these human areas were heavily used, but because they made up a small part of the monkeys’ human range, “contacts with humans and their structures were not constant and were spread in time.”

It’s regrettable that the authors “have neither quantified information about the time these monkeys spent around humans or their facilities nor of the type of contact”; however, they did observe humans feeding the vervets, vervets entering the dustbins and toilets, and in an echo of the game-lodge monkey thievery noted above, vervets stealing food from humans.

In their experiments, van de Waal and Bshary used “artificial fruits” devised of wooden boxes with Plexiglas doors on opposite ends; inside were eighth-pieces of apple. A monkey could open one door by pulling a knob, whereas for the other door, she or he had to slide the door to the left while holding a knob.

Demonstrators of the correct technique were vervets, not humans: alpha females in three of the groups, dominant males in the other three, all of whom had sole access to the box during a stage where only a single door was operative. The proper controls were employed, for instance, “the 2 groups that are in regular contact with humans differed with respect to the sex of the model and the type of door the model opened during demonstrations.”

For each group member, data were recorded as to whether she or he opened the box on the first trial and which door was first touched.

Neither sex of the demonstrator monkey nor door used to solve the task affected success on the box-opening, but group membership did: Vervets of the two groups with human contact fared better than vervets in the other four groups. Because length of the first manipulation at the box did not differ between successful and unsuccessful individuals, the authors reject an explanation of reduced neophobia (fear of new things or experiences) on the part of the human-contacting monkeys.

What is it, then, about proximity to our own activities that enhances the vervets’ capacities—or at least their responses? As the authors note, a next step would be to carry out this same test on captive vervet monkeys, to see if the captive animals’ were equally successful as the most successful monkeys in this experiment. Another idea, of course, would be to seek quantitative and qualitative information on what the wild monkeys actually do when in presence of humans.

Mainly, what grabbed me are implications of this research, not touched on in the article. Nonhuman primates are thrown, with every passing year, into greater proximity with humans. Sometimes the ensuing interactions are relatively neutral (think game lodges), sometimes they are uneasy (think crop-raiding monkeys). Is this landscape-sharing affecting the evolving behavior and cognition of other species in ways we don’t even realize?

It’s fascinating too to flip the question around: Could our own small-brained ancestors, living millions of years ago on the African savanna or in the rainforest, have learned certain skills by spending time near populations of non-human primates that were long-adapted to that local environment?


  1. January 14, 2011 10:59 AM EST
    I'm trying to think of this in terms of humans and gorillas, my study species, and only come up with the already (for me) known observation that we really shouldn't generalize behavior (gesture?) and cognitive abilities of species, or their causes, between different wild and captive groups, though some scholars seem to think we can. Closer to home, I'm thinking of cat behavior: in the last couple of weeks,it has been interesting watching our cat Annie gradually develop a whole new set of play behaviors and feeding and attention routines in the absence of her close companion cat who passed away about 3 weeks ago.
    - Joanne Tanner
  2. January 14, 2011 1:09 PM EST
    Joanne, I didn't have space to consider this in my post but the articles' authors do discuss what this means for relying heavily on captive studies. I actually like the way you phrase it better- to my mind it's not that captive studies are somehow giving us a flawed view of a species, but rather that we're learning not to generalize across populations, EITHER within captive/wild categories per species OR across those categories. I always discuss with students who are skeptical of captive studies how much we've learned about apes' capacities for tool use and communication via captive research (including your own work), that can then be used to ask questions in OTHER captive populations and in wild populations.
    - Barbara J. King
  3. January 14, 2011 3:09 PM EST
    Nice to have some real data on the very significant problem. Of course Kortland speculated that stone hammer and anvil use among chimpanzees was a result of proximity to humans and I have certainly heard Bill McGrew speculate that perhaps early hominins learned stone tool use from proximity to chimpanzees back when. I remember also wondering whether Joanne's observations of iconic gestures among San Francisco zoo gorillas might be the result of observing such gestures among the public watchers but decided that even in San Francisco such gestures were unlikely to have been made by humans at a zoo.
    - 5005
  4. January 14, 2011 3:46 PM EST
    Thanks for your comments, 5005! Clearly you're part or near to the primatological community... would you sign and let us know who you are? I realize an amusing bias in my own thinking: The suggestion that chimpanzees learned tool use from humans makes me want to respond 'oh but they are smart enough to figure it out on their own' whereas the suggestion that human ancestors might've learned from watching apes doesn't cause me any desire to defend! Obviously that's not entirely logical- it's just that for so long, so many nonhuman animals' abilities have been so drastically underestimated....
    - Barbara J. King
  5. January 14, 2011 3:53 PM EST
    Sorry for the anonymity--5005. I was confused by the "signature" name of the first box. Maybe it could be renamed "name". I thought it wanted a password, and I invented a simple one to remember (which I do not use for anything else).
    I am happy with the flattery that I am close to the primatological community--would you like to withdraw that now you know who I am?
    - Iain Davidson
  6. January 14, 2011 4:23 PM EST
    Now I will enthusiastically endorse my own earlier comment, Iain! Of course you are close to the primatological community. Your work is interdisciplinary and important to us! (The Authors' Guild which hosts my site is in charge of all the little boxes, alas. Sometimes I cannot get onto my own site because I cannot properly reproduce the gibberish letters/symbols required to prove I am not a robot.)
    - Barbara J. King

Selected Works

Why are animals so irresistible to us? Why do we live with and care so deeply about them? From the famous "art caves" of ice-age Europe, to the ancient villages where animals were first domesticated, to stories of apes, whales, dogs, and cats doing fascinating things today, King weaves together a scenario about the animal-human bond that encompasses our past, present and future.
Can scientists discover a prehistory of religion just as they have traced the evolution of technology, language, and art? What does compassion in chimpanzees, or burial patterns in our human ancestors and Neanderthals, tell us about the origins of religion? In Evolving God, named a Top Ten Religion Book for 2007 by the American Library Association, Barbara King explores these questions.
How do chimpanzees, bonobos, and gorillas-- the African apes -- communicate using body postures and gestures? Using her many years of experience studying these apes, Barbara King answers this question in a book that offers a new perspective on the evolution of language.