By: Fendy Lormine, Caroline Schad, Daniel Simosa, and Anna Walker (Stonehill College, BIO323: Evolution, Spring 2019)
A remarkable trait unique to humans is spoken language; it allows us to communicate our thoughts, emotions, and intentions with other humans. While not as advanced as human speech, other species use different means of vocalizations to express themselves. Nonhuman primates have a largely genetically fixed acoustic structure that they use to communicate with each other. Their vocalization system is mainly comprised of grunts and loud calls. This study focused on the genus Papio as a model organism. More specifically, they studied chacma (Papio ursinus), olive (P. anubis), and Guinea (P. papio) baboons. The aim of this research was to see how the variation in vocal repertoire and call structure relates to social system characteristics. They focused on how the baboons interact socially and how competition among males and females is affected by sexual selection. The researchers hypothesized that loud calls would differ more between species than grunts. They also predicted that sexual selection would lead to more pronounced differences between males of different species than between females.
To test their hypothesis, the researchers compared the structure of the main call types of Guinea and chacma baboons. They also analyzed the two types of calls (‘grunts’ and ‘loud calls’) in three baboon species mentioned earlier because they had they most comprehensive database for them. First, they used recorded vocalizations of the three species in their natural habitats. They recorded Guinea baboons between January 2010 and July 2011, as well as in February 2018 in Germany. They used vocalizations that were recorded from two groups of Olive baboons between November 2005 and April 2007 in Nigeria. They also used recordings from 84 chacma baboon vocalizations between January 1998 and June 1999 in Botswana. Following this, they performed a thorough analysis of the recordings using Avisoft-SAS Lab Pro 5.2 software. Finally, they conducted many statistical tests, which included a two-step cluster analysis, a stepwise discriminant function analysis, a Mantel Test algorithm, and a Kruskal–Wallis Test.
Based on the results, the researchers concluded that the chacma and Guinea baboons produced slightly shorter loud calls than the olive baboons. They also found that the males showed a slight variation in loud calls based on geographic location, whereas the females did not. The loud calls also appeared to be more differentiated than the grunts. Despite these slight variations, vocalizations were determined to be highly conserved throughout the different species and various social systems. This means that although there were slight differences, the vocalizations appeared to show similar patterns across all three species. This finding was particularly surprising to researchers because it indicates that the species’ social system characteristics does not result in increased vocal diversity. Another finding that appeared to differ from what was expected is that no evidence indicated that male calls were more differentiated that female calls. This is important because it implies that vocalizations do not appear to be a factor of sexual selection.
Overall this study gave insight into how the Papio species communicate with each other. Based on previous research in conjunction with their own data, the researchers suggested that vocal production in non-human primates, such as baboons, appears to be significantly less dependent on auditory input in comparison to humans. We depend almost solely on auditory input because we are obligate learners. This shows that nonhuman primate vocal production is more genetically constrained in comparison to humans. The slight differences between populations and species vocalizations within the genus Papio can be attributed to selective pressures shaping aspects of each populations’ call. However, this stays within the limits of the overall typical range of vocalization of the overall species. This research can help further our understanding of how other animals communicate, how humans evolved their complex form of vocalization, and what it might take for other animals to develop the same form of vocalization.