An international team of scientists, led by Dr. Tomos Proffitt from the Max Planck Institute for Evolutionary Anthropology, made a discovery that challenges long-held theories of human evolution. The study, published in the Proceedings of the National Academy of Sciences (PNAS) of the United States, reveals that yellow-breasted capuchin monkeys in Brazil inadvertently produce sharp stone flakes—tools previously attributed exclusively to early hominins—through their routine nut-cracking activities.
The research team documented the behavior of these capuchin monkeys, Sapajus xanthosternos, in the forest within a farm in Montes Claros, Minas Gerais. By using a large rock as an anvil and another smaller one as a hammer, the monkeys crack open seeds and nuts, inadvertently creating stone flakes in the process. These flakes bear a striking resemblance to some of the earliest known stone tools produced by hominins in Africa more than three million years ago.
"This is the first detailed analysis of a stone tool set from yellow-breasted capuchin monkeys in a wild environment," said Dr. Proffitt, the lead author of the study, according to the Postal do Algarve.
The analysis of lithic materials found at Fazenda Matos revealed remarkable similarities between the flakes produced by the capuchin monkeys and those associated with early hominins, such as Australopithecus. The capuchin-produced flakes exhibit the same fundamental characteristics as the oldest stone tools accepted by archaeologists, challenging the assumption that such tools were exclusively the product of intentional human activity.
"The research demonstrates that these sharp flakes, normally associated with the intentional production of tools in archaeology, can arise involuntarily during routine activities such as nut cracking," reported the Postal do Algarve. "This challenges the notion that early tool use was always intentional."
"Our results continue previous investigations on primates that use stone tools and show that the involuntary production of flakes should be considered a universal byproduct of percussive tool use in stone-using primates," explained Proffitt.
"They suggest that similar behaviors in early hominins, over three million years ago, may have led to the development of intentional flake production and, eventually, to the emergence of advanced stone tool technologies, such as the Oldowan and Acheulean," added Proffitt.
"These results challenge the assumption that all sharp flakes in the archaeological record represent the deliberate production of tools," said Lydia Luncz, the senior author of the article and group leader at the Max Planck Institute for Evolutionary Anthropology in Germany.
The study underlines the importance of examining the behaviors of modern primates to explore the evolutionary roots of human behavior. By comparing the lithic assemblage from Fazenda Matos with similar records from other primates, such as long-tailed macaques in Thailand, the team identified key differences influenced by the availability of raw materials and the size of the flakes.
"By incorporating the full spectrum of material records from primates and hominins, we can better understand the pathways that led to the emergence of lithic technology," stated Proffitt. "This research reinforces the need to broaden our perspective."
The discovery has implications for the study of human evolution. Since manipulating objects to create tools requires a more complex cognitive system than simply using available environmental tools, this finding prompts a reevaluation of when sophisticated minds emerged among human ancestors. The inadvertent production of stone flakes by capuchin monkeys suggests that early hominins might have similarly produced stone tools unintentionally, leading over time to the development of intentional tool-making practices.
Despite being conducted outside Africa and focusing on a primate far from the evolutionary lineage of Homo sapiens, the study promises to shake existing theories of human evolution. Brazilian researchers Paula Medeiros and Waldney Martins from the State University of Montes Claros participated in the study.
Capuchin monkeys have long fascinated scientists due to their skilled and intelligent behaviors. They can crack coconuts and other types of food by crushing them between two stones, a practice that has been observed for at least 3,000 years in the region. The study marks the first time such behaviors have been linked to the production of stone flakes resembling early hominin tools.
"Comparative analysis with other sets of flaked stone created by primates and hominins reveals that the intentional production of flakes is a universal component of the percussive use behavior of hammer and anvil, suggesting that similar behaviors of early hominins may have led to flaked stone technology," concluded Proffitt.
The article was written with the assistance of a news analysis system.