The ontogeny and phylogeny of non-verbal deixis

It is widely reported that our nearest living relatives, the great apes, lack a "declarative" mode of communication. There are few reports of any ape, regardless of rearing history, explicitly informing another about a state of the world as an apparent end in itself; see, e.g., Tomasello (2006). Historically, the term "declarative" has been used to classify a particular form of sentence or linguistic communication. However, the use of this concept to describe non-verbal communication stems from the introduction by Bates, Camaioni, and Volterra (1975) of the term "proto-declarative" to describe pointing by human babies with the apparent goal of fostering a state of shared apprehension of distant events or objects with a communicative partner. But a declaration is a linguistic act; it is therefore not immediately clear if the term should be applied to non-verbal communicative behaviour by either nonhuman primates or preverbal humans (Leavens 2004a; Leavens & Hopkins 1998; Racine 2005; Susswein & Racine in press-a). And apes in captivity adopt numerous non-verbal deictic behaviours, including manual pointing. Although observations of manual pointing are limited almost entirely to captive great ape populations, recent studies indicate that other manifestations of non-verbal deixis, such as directed scratching (Pika & Mitani 2006), may be much more common in wild ape populations than heretofore appreciated. Although older children and perhaps some enculturated apes occasionally point to share experience as an end in at itself, here we argue that pointing, and other non-verbal deictic behaviours, serve fundamentally instrumental functions (Racine, Leavens, Susswein & Wereha in press). As a result, we will further argue that the cognitive origins of non-verbal deictic acts are similar, regardless of the ostensible motivation of the signaler. To do so, we review research on deixis in the great apes, discuss the distinction between imperative and declarative communication in greater detail and then consider the meaning of proto-declarative pointing. We conclude that epigenetically heritable caregiving environments of hominins, probably beginning in the Plio-Pleistocene, foster manual pointing in early infancy (Davidson 1997; Leavens, Hopkins & Bard 2005a) and implicate an interaction of hominoid cognitive capacities with hominin-unique features of early infancy. Hominins were, thus, pre-adapted for one aspect of the faculty of language in the broad sense: joint attention (Hauser, Chomsky, & Fitch 2002).