title: Manipulation complexity in primates coevolved with brain size and terrestriality.
abstract: Humans occupy by far the most complex foraging niche of all mammals, built around sophisticated technology, and at the same time exhibit unusually large brains. To examine the evolutionary processes underlying these features, we investigated how manipulation complexity is related to brain size, cognitive test performance, terrestriality, and diet quality in a sample of 36 non-human primate species. We categorized manipulation bouts in food-related contexts into unimanual and bimanual actions, and asynchronous or synchronous hand and finger use, and established levels of manipulative complexity using Guttman scaling. Manipulation categories followed a cumulative ranking. They were particularly high in species that use cognitively challenging food acquisition techniques, such as extractive foraging and tool use. Manipulation complexity was also consistently positively correlated with brain size and cognitive test performance. Terrestriality had a positive effect on this relationship, but diet quality did not affect it. Unlike a previous study on carnivores, we found that, among primates, brain size and complex manipulations to acquire food underwent correlated evolution, which may have been influenced by terrestriality. Accordingly, our results support the idea of an evolutionary feedback loop between manipulation complexity and cognition in the human lineage, which may have been enhanced by increasingly terrestrial habits.
authors.affiliation: Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Sandra A
authors.initials: SA
authors.lastname: Heldstab
authors.affiliation: Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Zaida K
authors.initials: ZK
authors.lastname: Kosonen
authors.affiliation: University of Helsinki, Centre of Excellence in Intersubjectivity in Interaction. P.O.Box 4, Vuorikatu 3, 00014 Helsinki, Finland.
authors.forename: Sonja E
authors.initials: SE
authors.lastname: Koski
authors.affiliation: Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Judith M
authors.initials: JM
authors.lastname: Burkart
authors.affiliation: Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Carel P
authors.initials: CP
authors.lastname: van Schaik
authors.affiliation: Department of Anthropology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Karin
authors.initials: K
authors.lastname: Isler
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D003071:Cognition; D005247:Feeding Behavior; D011323:Primates; D012919:Social Behavior