Study Finds Bigger Gorillas are Better at Attracting Mates and Raising Young

Posted on May 4, 2012

Conservationists with the Wildlife Conservation Society and the Max Planck Institute for Evolutionary Anthropology have found that larger male gorillas living in Congo rainforests appear to be more successful than smaller ones at attracting mates and even raising young. The study was conducted over a 12-year period in Nouabale-Ndoki National Park in the Republic of Congo.

The researchers selected three physical factors for measurement: overall body length; the size of the adult male's head crest; and the size of the gluteal muscles on the animal's posterior. The researchers then compared data on individual size with information on group dynamics to explore possible correlations between physical characteristics of adult males, the number of female gorillas connected to males, and the survival rates of an adult gorilla's offspring.

The results of the study revealed that all three characteristics were positively correlated to an adult male's average number of mates. In other words, the bigger the adult male, the more mates it had. An unexpected finding from the study was that only head-crest size and gluteal muscles were strongly related to offspring survival (measured as infants that survived to weaning age) and overall reproductive success (measured as the number of surviving offspring).

Thomas Breuer of the Wildlife Conservation Society and lead author of the study, says, "Our findings of correlations between physical traits and male reproductive success could be considered evidence of a selection process in gorillas, but it is not yet proof. More studies would be necessary to determine the links between morphology and fitness in this and other long-lived species."

The study appears in a recent edition of Journal of Human Evolution. The authors of the study include: Thomas Breuer of the Wildlife Conservation Society and the Max Planck Institute for Evolutionary Anthropology; and Andrew M. Robbins, Christophe Boesch, and Martha M. Robbins of the Max Planck Institute for Evolutionary Anthropology.

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