One intriguing hypothesis about the origins of human language is that it emerged as a 'social tool,' facilitating our abilities to maintain relationships with an increasing number of people (the "social grooming hypothesis"). The basic idea is that social grooming (which facilitates a bond with only one individual) is replaced by vocal 'grooming' (which facilitates bonds with several individuals, simultaneously). Indeed, social bonds have adaptive value for both humans and non-human primates. Thus, if vocal contact represents an efficient way to maintain relationships, then selection should favor its development. Despite a great deal of theoretical support, however, the social grooming hypothesis has yet to be tested empirically. Geladas provide an excellent model to test this because they are highly social, exceptionally vocal, and uniquely time-constrained because they must spend much of their day foraging on grass. This research by doctoral student Elizabeth Johnson (University of Michigan), under the supervision of Dr. Jacinta Beehner, will explore the strategies that female geladas employ to maintain their social networks, with a specific emphasis on when vocalizations are used, the responses they elicit, and whether such vocal contact supplements or replaces social grooming when time budgets are particularly strained. By utilizing a combination of methods, including behavioral observation, social network analysis, analysis of 'stress' hormones, and acoustic analysis of recorded vocalization, this research will elucidate one possible route by which human ancestors may have maintained social bonds, allowing for larger groups and greater group cohesion.
Results from this study not only contribute to a better understanding of female gelada social relationships, but also provide a comparative dataset for on-going collaborative projects on closely related species (e.g., anubis and hamadryas baboons). Further, this research extends beyond academia, raising awareness about the study site (the Simien Mountains National Park of Ethiopia, a World Heritage Site in Danger) and the study species, an endemic species to the highlands of Ethiopia with a conservation status labeled as "Threatened" by the IUCN Red List. Finally, this doctoral dissertation research project contributes to the long-term viability of the park by hiring a local field assistant (providing both employment opportunities as well as continuing education for these young adults), working closely with park officials, and providing educational lectures to Ethiopian nationals.
