Cracking the (Nut) Case: The Evolution of Tool Use in Capuchins and Other Primates

In Life Season 1, Episode 10, Brazilian brown-tufted capuchin monkeys are depicted using tools to obtain food. Specifically, they use large stones that can be nearly half their body weight to crack open palm nuts. While tool use is often viewed as a purely human trait, there is evidence of nonhuman tool use across the animal kingdom, especially among primates, such as capuchin monkeys (Cebus apella) [1].

It is established in previous work that a tool can be either manufactured, in which it is actively made by an organism to achieve an end, or employed, in which it is simply taken from the environment and used in its current state [2]. According to these criteria, capuchin tool use is not an example of tool manufacturing, but experimental work has determined that these primates are capable of both tool employment and manufacture [2]. Oftentimes, primates develop these tools for extraction of insects and nuts, which provide fat and protein that is frequently lacking from the primate diet [3]. The tool manipulation skills required for their applications are supported by a large brain size in relation to total body weight, and in the case of capuchins, an increased spinal cord size [4].

Although the tool use itself does not appear to be the result of genetic “instincts” per se, it does appear that the need to observe a more educated other for guidance on complex tasks, such as food extraction, evolved in capuchins and other primates as a necessity for living in a complex society [1]. This underscores one way in which behavioral traits may evolve in a population, through individuals evolving to be predisposed to learn skills from authority figures, rather than the skills being known to the organism through some inborn inherited mechanism.

(Life, Season 1, Episode 10, starting at approximately 39:50)

by Paul Young

References

1. Ottoni EB, de Resende BD, Izar P. 2005. Watching the best nutcrackers: what capuchin monkeys (Cebus paella) know about others’ tool-using skills. Animal Cognition 24: 215-219.
2. Westergaard GC, Fragaszy DM. 1987. The Manufacture and Use of Tools By Capuchin Monkeys (Cebus apella). Journal of Comparative Psychology 101(2): 159-168.
3. Melin AD, Young HC, Mosdossy, KN, Fedigan LM. 2014. Seasonality, extractive foraging and the evolution of primate sensorimotor intelligence. Journal of Human Evolution 71: 77-86.
4. Rilling JK, Insel TR. 1999. The primate neocortex in comparative perspective using magnetic resonance imaging. Journal of Human Evolution 37: 191-223.