1. Ancient Stones in Taï National Park Show Chimpanzees Used Tools About 4,300 Years Ago
The stones were discovered at three sites within Taï National Park in Côte d’Ivoire. Dating places them at approximately 4,300 years old [1]. Starch residues on the stones indicate that five different types of nuts were cracked using them [1]. The decisive evidence came from the contents of these residues. According to National Geographic, many of the traces matched the nuts that modern chimpanzees eat today [2]. Based on this, researchers concluded that these were tools used by chimpanzees, not by humans.
It is important to note that this is not a claim about the "first tool use in the world." It simply means this is the oldest evidence found at these specific locations. The technique of cracking nuts with stones may have existed for a long time. So, how do chimpanzees in today’s forests use these stones?
2. Chimpanzees in Bossou, Guinea, Crack Oil Palm Nuts with an Anvil Stone and a Hammer Stone
In the Bossou forest in Guinea, wild chimpanzees use two stones to crack oil palm nuts. Researchers from Kyoto University have been studying this population since 1976 [3]. The method involves placing one stone on the ground as an anvil. The nut is placed on top of it. The chimpanzee holds a second stone in its hand and swings it down like a hammer to strike the nut. The roles of the anvil and the hammer are clearly separated.
The difficulty of this skill lies in using the left and right hands for different tasks. The Bossou introduction page describes nut-cracking as one of the most sophisticated behaviors among chimpanzee tool use [3]. While it seems possible to learn just by watching, when and how do young chimpanzees acquire this skill?
3. At Age 2.5, Young Chimpanzees Copy the Movements but Cannot Yet Crack Nuts
A study conducted between 1992 and 1995 observed three young chimpanzees in Bossou. Researchers analyzed 692 scenes of stone and nut handling and 150 scenes of adult behavior [4]. The findings revealed a specific order of development. By 2.5 years old, young chimpanzees can perform basic actions such as holding a stone and placing a nut. However, they cannot yet connect these actions in sequence to actually crack the nut [4]. They begin attempting to crack nuts with an anvil and hammer around 3.5 years old [4].
It is a mistake to interpret "cracking at 3.5" as proficiency. This "starting to crack" means the challenge begins; becoming skilled happens much later. The components of the action are present, but it takes about a year to connect them. What happens after this initial start?
4. Chimpanzees Get Better at Nut-Cracking Until About Age 11, and Individuals Differ
Regarding the age at which chimpanzees become capable of using stone tools, Kyoto University announced in 2009 that chimpanzees typically begin to use stone tools effectively between 4 and 5 years old [5]. Combining this with the earlier finding that they start attempting at 3.5 years, say skill acquisition progresses around ages 3 to 5. However, becoming capable is not the end of the process.
A study published in December 2024 analyzed over 800 hours of video footage, covering 3,882 instances of 21 chimpanzees cracking nuts in Bossou between 1992 and 2017 [6]. Four indicators of cracking efficiency increased with age until 11 years old. Furthermore, clear differences were observed between individuals of the same age and sex; some were more skilled than others [6]. From the initial basic actions at 2.5 years to efficiency indicators increasing until age 11, the period spans about 8.5 years. What clues do children use to improve during this long time?
5. Chimpanzees Choose Whether to Use Stones Based on Nut Hardness, and Groups Differ
Whether chimpanzees use stones depends on the type of nut. In the Taï forest of Côte d’Ivoire, it is said that they use stones for very hard nuts (*Panda oleosa*) and wooden hammers for softer nuts (*Coula edulis*). When only stones are available, they tend to choose heavy, hard stones for hard nuts and lighter stones for soft nuts [7]. This is a tendency, not a strict rule.
The type and size of stones also vary by group. A 2022 research summary notes that the stone types, sizes, and anvil sizes (some exceeding 1 meter) differ between groups. Possible reasons include stone selection methods, availability, and the combination of nut types [8]. This article also reports that some groups have their own archaeological records dating back about 4,300 years [8]. The stones from the first section are part of this long history.
6. Chimpanzees and Human Hunter-Gatherers Both Need Years to Learn Nut-Cracking
How does the time required to learn nut-cracking compare between chimpanzees and humans? A 2019 study compared chimpanzees in the Taï forest with hunter-gatherers living in Mbendjele, Congo, as they learned to crack the same hard nut (*Panda oleosa*) [9]. Both required years of practice to reach proficiency. Interestingly, chimpanzees reached adult-level efficiency earlier than the human children [9]. "Teaching" behaviors were also observed in both groups [9].
This does not mean "chimpanzees are smarter than humans." The comparison involves different tools and environments. The key finding is that the skill of cracking the same nut is passed down over many years in both species. Young chimpanzees and human children alike acquire skills over years within their daily lives.
Both chimpanzees and humans require years of practice to reach proficiency, with chimpanzees reaching adult efficiency earlier in this specific task.
7. Try a Desk Activity That Shows How Hard It Is to Use Two Hands for Different Jobs
You can simulate the difficulty at a desk using a plate as an anvil. Place crumpled paper on the plate. Keep your left hand firmly pressing the plate while using your right fingers to move the paper from one edge to the other. If the holding hand shakes, the plate slips. Next, switch hands and repeat the task. While different from actual nut-cracking, this helps you physically understand the difficulty of separating the role of the supporting hand from the moving hand.
In this article, the age range appears to change significantly. From the basic actions seen at 2.5 years to the efficiency increase at 11 years, the span is about 8.5 years. Counting from the start of cracking attempts at 3.5 years, it is about 7.5 years. Even after basic actions are visible, the period of efficiency improvement continues for a long time. For further reading, Kyoto University’s announcement [5] and the Nature Asia Japanese highlight [6] are available in Japanese. The original papers in English can be found via the links in the source list.