Wild macaques challenge the origin of intentional tool production

Abstract

Intentionally produced sharp-edged stone flakes and flaked pieces are our primary evidence for the emergence of technology in our lineage. This evidence is used to decipher the earliest hominin behavior, cognition, and subsistence strategies. Here, we report on the largest lithic assemblage associated with a primate foraging behavior undertaken by long-tailed macaques (Macaca fascicularis). This behavior results in a landscape-wide record of flaked stone material, almost indistinguishable from early hominin flaked pieces and flakes. It is now clear that the production of unintentional conchoidal sharp-edged flakes can result from tool-assisted foraging in nonhominin primates. Comparisons with Plio-Pleistocene lithic assemblages, dating from 3.3 to 1.56 million years ago, show that flakes produced by macaques fall within the technological range of artifacts made by early hominins. In the absence of behavioral observations, the assemblage produced by monkeys would likely be identified as anthropogenic in origin and interpreted as evidence of intentional tool production.

Fig. 1.. The long-tailed macaques on Lobi Bay in Phang Nga Bay (Thailand) crack oil palm nuts using stone hammers and anvils, leaving a visible archaeological record of lithics and nut debris.

Location of Lobi Bay (A) and example of long-tailed macaque nut-cracking site and associated behavior (B). Red arrows denote detached flakes, and black arrows denote hammerstones.

Fig. 2.. Examples of limestone flakes and flaked pieces produced unintentionally during long-tailed macaque nut cracking.

Selected examples of flaked pieces and complete flakes from Lobi Bay. (A) Refitted flaked hammerstone showing a total of 24 flake detachments during three separate phases of reduction and selected associated complete flakes. (B to D) Examples of flaked pieces with multiple superimposed flake detachments. (E to K) Examples of complete flakes with clear platforms and bulbs of percussion. (L to M) Dorsal-ventral flake refits illustrating recurrent unidirectional flake detachments. (N) Comparative Oldowan flakes from BD1 (5). White dots represent impact points associated with flake detachments; black arrows represent the directionality of a flake scar; and white arrows indicate the location of an impact point on a flake platform.

Fig. 3.. Jitter plots showing the high degree of overlap in both dimensional and technological measures for both macaque flakes and flaked pieces when compared to Plio-Pleistocene assemblages.

Comparative analysis of selected quantitative and technological attributes for Lobi Bay macaque, Oldowan and Lomekwian flakes (A) and flaked pieces (B). Note that all macaque datapoints fall within the range of variation for intentional hominin lithic technology. Mass is reported on a log₁₀ scale. Abbreviations reported for reduction patterns are detailed in the Supplementary Materials. EPA, external platform angle.