Primate archaeology is a fast growing field. While archaeology usually refers to the study of the human past through the excavation of past tools, remains, and civilizations, primate archaeology unearths the technological (tool use) past of our primate relatives as well as observes tool use by primates in real time (Click here to learn more). Each year, scientists make new discoveries about primates and their behaviors that prompt questions about the full extent of our primate relatives’ cognition and how it relates back to our own cognitive evolution.
Chimpanzees shine in this research because they are one of the most technologically adept primate species. For instance, chimpanzees in the wild have demonstrated more than 40 different tool type behaviors, ranging from feeding, grooming, and comfort to protection, socialization, and even curiosity (like poking a plant with a stick to see what happens). Chimpanzee tool sites were also the first non-hominin (hominin refers to humans and our ancestors) sites to be archaeologically excavated, although the findings at the 4,000 year old chimpanzee tool site, are very different from what you might find at an early hominin stone tool site. On the surface, chimpanzee tool sites look similar to hominin sites – they both have tools like hammerstones, anvils, flake debris, and remnants of food waste products (e.g., nutshells). However, how the tools were used appears very different from early hominin sites. Hominins would intentionally use the stone tools to make stone flakes that would then be used to process food, whereas at chimpanzee sites, stone tools were used to directly process the food (e.g., placing the nut on the anvil and smashing it with the hammerstone). When done repeatedly, stone flakes would be unintentionally chipped off the anvils and hammerstones as debris, rather than being used to process food.
While great apes (chimpanzees, bonobos, gorillas, and orangutans) are some of the most adept and frequent users of tools both in the wild and in captivity, there are also monkey species that habitually use tools for subsistence in the wild. In the past few years, these monkeys have been taking the spotlight in primate archaeology research as this field grows.
Two main monkey species have demonstrated stone tool use in the wild: long-tailed macaques in Thailand, and capuchins in South America. The use of stone tools is archaeologically significant because they do not decay or degrade like organic materials (sticks, twigs, stems, etc.). Thus, it provides a more definitive date for when the tools were used, and because stone tool use can demonstrate several different behaviors, they are good indicators for cognitive abilities.
Both groups of monkeys use stone tools to procure food. The macaques crack open oyster shells, and the capuchins use similar techniques to crack open nutshells. This is one of the simplest behaviors with stone tools and one you would expect at the earliest point in tool use evolution. There’s some evidence to show that capuchins are selective in their material choice, choosing heavier, more compact hammerstones to smash nuts, hinting at evidence of forethought in the tool use process. Still more interesting are the recent studies comparing the debitage (the flakes, stone debris, and rocks) from the tool behaviors at the archaeological sites made by the capuchins, and experimental stone tools made by our more recent human ancestors. Flakes that come off the hammerstones and anvils from monkey tool sites look, paradoxically, incredibly similar to the flakes found at human sites in the Americas because they are smaller; this is due to the advanced stone tool industries used by modern humans versus early hominins. When hominins in Africa were flaking cobblestones, the goal was to get a flake large enough to hold in their hand, like a knife or a scrapper, whereas modern humans in the Americas would be flaking cobblestones with the intention of using smaller flakes to make things like arrowheads and bladelettes. As a result, the flake debris is much smaller, and closer in size to what might be present at a monkey site.
This evidence has now led to an intense debate in South American archaeology on whether some of the earliest archaeological sites in Brazil (dating back as far as 50,000 years ago) are human-made or monkey-made! This is incredibly important because these archaeological sites have been crucial to archaeologists’ understanding of the timeline of when humans arrived in the Americas. The sites at the center of the debate are entirely made of stone tool material and debitage, which is unusual for a human site for that time period. Most human sites at that time included hearths, evidence of living spaces, potentially decorative items, etc., but these sites don’t. At the time of their discovery, they were still attributed to humans, since monkeys weren’t known for their stone tool skills. Additionally, primate archaeologists are arguing that the specific material at the sites closely reflect what a modern capuchin nut-cracking site looks like – hammerstones were brought in from the surrounding areas, but the anvils are stones that have not moved from their original spot. However, that could mean nothing since anvils tend to be very big and heavy, and even humans wouldn’t want to move a large rock when they don’t have to. With the current evidence it’s hard to really say who made these stone tool sites. Further analyses of the tools can provide evidence to support one hypothesis over the other. Use-wear analysis of the flakes can show whether the flakes were used to process food; if they were, the data would support a human tool site, since there’s no current evidence that modern nonhuman primates (not even chimps) use stone flakes for processing. Debris cluster analysis could inform researchers how the flake debris was spread out. A more chaotic, less patterned spread would suggest capuchin since humans tend to be more methodical and precise when flaking rocks and the debris would fall all in one place.
If these sites prove to be monkey-made they’ll be some of the oldest non-human primate archaeological sites in the world. This would significantly push back the date that primatologists understand non-human primates to have begun using tools, and can have a significant impact on how we understand the cognitive abilities of our primate relatives. Evidence of tool use in great apes, macaques, and capuchins suggests that the cognitive abilities necessary for tool use (working memory, motor skills, forethought, etc.) was present as far back as our last common ancestor with these other primates (over 30 million years ago). Scientists once thought that the ability to selectively use tools was a uniquely human trait. However the more we uncover about tool use in other primates, the more cognitive abilities once considered exclusive to humans are revealed to be deeply embedded into our primate history. This shows that we are more alike than once thought. So, tell your archaeologists friends to beware! Their simple stone tool sites might not be human after all.
Edited by Joe Vuletich and Brianna Best