International Journal of Primatology
23 (1): 85-104, February 2002
All rights reserved
Karin L. Enstam
Department of Anthropology, University of California,
Davis, California; klenstam@ucdavis.edu
Lynne A. Isbell
Department of Anthropology, University of California,
Davis, California
Thomas W. De Maar
Ol Jogi, Ltd., Nanyuki, Kenya
Abstract
Infanticide by males has been hypothesized to be a naturally
selected behavioral strategy that increases the infanticidal male's
reproductive success. The sexual selection hypothesis has been challenged via
alternative, nonadaptive hypotheses that dispute its empirical and theoretical
bases. Two of the most widely recognized alternatives are the social pathology
hypothesis, in which infanticide results from overcrowding or recent human
disturbance, and the generalized aggression hypothesis, in which infanticide is
an epiphenomenon of increased male aggression. We report the first case of
infanticide in wild, seasonally breeding patas monkeys (Erythrocebus patas)
living at a low population density in a stable habitat, conditions which do not
support the social pathology hypothesis. Its exceptional occurrence is
consistent with the sexual selection hypothesis: over a 7-year period the
infanticidal male was the only one of 13 resident males that was not present
during the actual conception season but was present during the following birth
season. Also consistent with this hypothesis, mothers were differentially
targeted for male aggression, which increased sevenfold during the days
surrounding the infanticide and then decreased to baseline levels after the infanticide.
Aggression targeted at mothers does not support the generalized aggression
hypothesis. As predicted by the sexual selection hypothesis, females began
soliciting mating immediately after the infanticide, despite its occurrence in
the nonconceptive season.
Keywords
Erythrocebus patas, infanticide, patas monkeys,
seasonal breeding, sexual selection hypothesis