EcoMinga’s Primates 3: Tool User!

Genetic evidence suggests that the population of ancestral humans was once perhaps as small as a few thousand individuals. We escaped extinction by a hair, but what if we hadn’t? Would some other primate lineage have produced civilization-builders? If so, which lineage would it be?

Probably most people would guess that our replacement would descend from one of the other great apes: bonobos, chimps, gorillas, or orangutans. A reasonable guess, but I’d like to suggest there’s another primate in the running. Watch and be amazed by this “Life” video, narrated by Sir David Attenborough:

These capuchin monkeys are manipulating stones often more than half their body weight, the largest tools in relation to body size of any non-human animal. And they somehow carry these heavy stones long distances from riverbeds to their anvil sites, even climbing cliffs with them. This is not only a challenging physical feat but also a complicated cognitive task involving long-delayed rewards. This behavior is not instinctive –observations suggest that it takes many years for a capuchin to master the task. Chimps are the only other non-human primates with such complex tool use. But chimps that use stones to break nuts do not use large rocks, and their movements during nut-breaking are less specialized (less unusual compared to their ordinary repertoire of movements) than those of capuchins.

The scientific community has focused on the tool use of Brazilian populations of the Brown Tufted Capuchin, Cebus apella, the species in the Attenborough video. In our EcoMinga reserves, we do not have this species, but we do have the White-fronted Capuchin, Cebus albifrons in our Cerro Candelaria, Naturetrek, and Rio Zunac reserves. One of our forest caretakers, Luis Recalde, recently managed to photograph this White-fronted Capuchin in the Cerro Candelaria Reserve:

White-fronted Capuchin, Cebus albifrons

White-fronted Capuchin at about 1600m elevation in our Cerro Candelaria Reserve. Photo: Luis Recalde/EcoMinga.

On another occasion, Juan Pablo Reyes and our caretakers set up a camera trap near that reserve to discover what animal was eating our neighbors’ corn. The culprit turned out to be a sneaky White-fronted Capuchin:

I haven’t noticed reports in the scientific literature about stone tool use in the White-fronted Capuchin, but some friends of mine (Juan Medina, Oscar Valenzuela) have repeatedly observed complex behaviors in this Ecuadorian species. The best place to observe these behaviors is in the jungle town of Misahualli, home of a wild population of White-fronted Capuchins that has adapted to human city life. Juan Medina, a guide who spent much time in the town, tells me that just like the Brazilian Cebus apella, the monkeys there collect large pounding rocks along the rivers and carry them (sometimes using both hands) into the town, where they use them to break hard food objects. Juan observed that they also use carefully-chosen sticks (again, brought from a distance) to dig out carpenter bee larvae from their tunnels. Here is a short clip on YouTube made by a visitor in Misahualli. The stone tool use by the White-fronted Capuchin is clearly visible:

A few more clips of tool use in Misahualli capuchins:

We shouldn’t be surprised by capuchins’ exceptional cognitive abilities. The ratio of brain-to-body weight in capuchins is higher than in all other non-human primates– twice as high as for chimps, and almost as high as in humans (calculated from Table 1.1 of Lonsdorf et al. 2010). This is not necessarily a reliable indicator of intelligence, but it does suggest that capuchins might be unusual compared to other primates.

Capuchins are still evolving. Who knows what they might become in the distant future if they survive? These are bottleneck years for capuchins, and by helping to save them now, we keep their evolutionary path alive. In a couple million years capuchin geneticists in their treetop labs might be thanking their monkey gods for getting them through this population bottleneck. I don’t suppose they will realize it was actually humans like us that kept their evolutionary path going, but it makes me happy to think we might be helping to give them that future.

Lou Jost

Additional reading:

Lonsdorf et al 2010. The Mind of the Chimpanzee: Ecological and Experimental Perspectives. University of Chicago Press.

3 thoughts on “EcoMinga’s Primates 3: Tool User!

  1. Pingback: Spectacled Bear caught raiding our neighbors’ cornfield | Fundacion EcoMinga

  2. Pingback: Quick visit to our Rio Zunac field station | Fundacion EcoMinga

  3. Pingback: Monkey killer: Black-and-chestnut Eagle, Spizaetus isidori | Fundacion EcoMinga

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