On the evolution of handedness: evidence for feeding biases
Date
2013
Authors
Flindall, Jason W.
Gonzalez, Claudia L. R.
Journal Title
Journal ISSN
Volume Title
Publisher
Public Library of Science
Abstract
Many theories have been put forward to explain the origins of right-handedness in humans. Here we present evidence that
this preference may stem in part from a right hand advantage in grasping for feeding. Thirteen participants were asked to
reach-to-grasp food items of 3 different sizes: SMALL (CheeriosH), MEDIUM (Froot LoopsH), and LARGE (Oatmeal SquaresH).
Participants used both their right- and left-hands in separate blocks (50 trials each, starting order counterbalanced) to grasp
the items. After each grasp, participants either a) ate the food item, or b) placed it inside a bib worn beneath his/her chin (25
trials each, blocked design, counterbalanced). The conditions were designed such that the outward and inward movement
trajectories were similar, differing only in the final step of placing it in the mouth or bib. Participants wore Plato liquid crystal
goggles that blocked vision between trials. All trials were conducted in closed-loop with 5000 ms of vision. Hand kinematics
were recorded by an Optotrak Certus, which tracked the position of three infrared diodes attached separately to the index
finger, thumb, and wrist. We found a task (EAT/PLACE) by hand (LEFT/RIGHT) interaction on maximum grip aperture (MGA;
the maximum distance between the index finger and thumb achieved during grasp pre-shaping). MGAs were smaller during
right-handed movements, but only when grasping with intent to eat. Follow-up tests show that the RIGHT-HAND/EAT MGA
was significantly smaller than all other hand/task conditions. Because smaller grip apertures are typically associated with
greater precision, our results demonstrate a right-hand advantage for the grasp-to-eat movement. From an evolutionary
perspective, early humans may have preferred the hand that could grasp food with more precision, thereby maximizing the
likelihood of retrieval, consumption, and consequently, survival.
Description
Sherpa Romeo green journal: open access
Keywords
Right-handedness , Right-handed movements , Right-hand dominance , Maximum grip aperture , MGA , Grasp-to-eat , Grasp-to-place , Kinematics
Citation
Flindall, J. W., & Gonzalez, C. L. R. (2013). On the evolution of handedness: evidence for feeding biases. PLoS ONE, 8(11): e78967. doi:10.1371/journal.pone.0078967