Hypothesis: Yawn serve the purpose of
reducing arousal in groups of primates while
reinforcing dominance hierarchies. Yawns signal
vigilance or relaxation. Observing of
conspecific's yawns may "precipitate" the
observer's need to yawn. Method: Observation of
yawning, yawning context, yawning frequency in
primates. Observationof which individuals yawn,
their ages, sex, ranking, and behavioral
patterns.
Results: Yawning was shown to reveal
canines. Yawning shows possible disinterest in
other individuals when displayed during play or
mating circumstances. Yawning occurred before
and after interaction of a hierarchical
(aggressive) or sexual nature. Yawns
"precipitated" in mangabey's and macaques,
expecially of the same age and social status,
following an individual's initial yawn.
Discussion/Conclusions: Yawns serve
as arousal indicating and reducing gestures,
while at the same time reinforcing dominant
identity. There are two kinds of yawns :
the yawn of inactivity (the
physiological yawn, which evolved under hormonal
pressures)
the yawn of
emotivity (the tension yawn, which
evolved under social selective pressures).
Affective yawns take place after social
interactions and related to a decline in
vigilance level. Yawns with canine exposure
especially in sexually dimorphic taxa, and
especially with males who expose prominent
canines. Anabolic effect of androgens on older
age causes higher frequency of yawns.
