Flexibility in Great Ape Vocal Production

Abstract

Traits that are often cited to distinguish spoken language from other, nonhu-man vocal communication systems range from the way that language combines a finite number of sounds into an infinite number of meaningful expressions (Collier et al. 2014; Hurford 2011), to its rich semantic layer (Hurford 2007). However, a large body of comparative data on the vocal behavior of primates has emerged over the last five decades indicating these differences could be considered continuous or quantitative in nature (Watson et al. 2015a; Zuber-bühler 2005; Zuberbühler, Cheney, and Seyfarth 1999). For example, a number of monkey and ape species (and, indeed, non-primate mammals and birds, see Gill and Bierema 2013; Townsend and Manser 2013) use vocalizations to re-fer to external objects and events in the environment in a way that appears comparable to language’s semanticity or reference (Clay, Smith, and Blumstein 2012; Seyfarth, Cheney, and Marler 1980; Slocombe and Zuberbühler 2005, al-though see Townsend and Manser 2013; Wheeler and Fischer 2012). Moreover, primates are also capable of combining sounds and calls together in different ways to encode meaning (Cäsar et al. 2013; Clarke, Reichard, and Zuberbühler 2006; Clay and Zuberbühler 2009; Spillmann et al. 2010) and even, in some instances, to increase communicative output (Arnold and Zuberbühler 2006; Collier et al. 2014; Coye, Zuberbühler, and Lemasson 2016; Coye et al. 2015; Ouattara, Lemasson, and Zuberbühler 2009). These rudimentary semantic and syntactic abilities in our close relatives have been argued to support a gradual evolutionary scenario for human language abilities (Arnold and Zuberbühler 2006; Slocombe and Zuberbühler 2005; Zuberbühler 2005), building on pre-existing cognitive and communicative capacities in our primate ancestors.