The evolutionary origins of group-mindedness: comparative studies with apes and equines

概要

Humans work together and collaborate on massive scales nearly unparalleled elsewhere in nature.
They also kill, wage wars, and commit genocide. While these behaviours are often considered
antithetical, evolutionary considerations suggest a common history. In my doctoral thesis, I aimed
to conduct a systematic empirical investigation of the roots of “group-mindedness,” through
studies of our closest relatives and closest companions. To do this, I studied group-mindedness
from three levels: the behavioural products (group cohesion), the selection pressures (especially
intergroup competition), and the proximate hormonal mechanisms (highlighting the neuropeptide
oxytocin). In particular, I studied where these levels intersect, focusing on how oxytocin affects
group cohesion, how oxytocin interacts with responses to outgroup sensory cues, and how
outgroup cues themselves affect group cohesion. Methods consisted of high-resolution eyetracking as well as broader-scale observation of free interaction. As study species, I worked with
captive bonobos and chimpanzees, and semi-free ranging domestic horses. Bonobos and
chimpanzees (our two closest relatives) differ drastically in group-based behaviour despite
relatively recent divergence. Horses are phylogenetically more distant, but share with us a history
of domestication and, like us, form complex multi-level societies in natural conditions. These
species thus make ideal targets for comparative research on the evolution of group-mindedness.
Methods
In the first set of studies, the effect of outgroup vocalizations on ingroup social behaviour was
compared to control (crow vocalizations). Observation was conducted before, during, and after
presentation of stimuli. The first study focused on chimpanzees, while the second focused on
bonobos. In the chimpanzees study, semi-monopolizable bundles of food were given to group
after stimuli played, while in the bonobo study this was replaced by a silent period of observation.
The second set of studies aimed to validate oxytocin administration as a tool for researching social
cognition in great apes. A non-invasive procedure to administer exogenous oxytocin to great apes
was developed. In the first of these studies, participants watched stimuli from a wide variety of
social contexts after administration of oxytocin or placebo while their eye-gaze was recorded. In
the second study, the same administration procedures were used to investigate how oxytocin
affects the allocation of attention to ingroup and outgroup stimuli. Matched-sex image pairings
were presented, each featuring headshots of one ingroup member and one outgroup member. In
the third ape oxytocin study, whole subgroups of female bonobos simultaneously were given
either oxytocin or placebo, after which their naturalistic social behaviour was recorded.
Finally, in the last study, horse positioning across five groups was recorded in large fields after
receiving either oxytocin or placebo control, administered using a custom-designed detachable
mask. Group-level metrics of association were then analyzed for each experimental day, as well as
association between dyads. ...