Social cognition and the evolution of language: constructing cognitive phylogenies

Abstract

Human language and social cognition are closely linked: advanced social cognition is necessary for children to acquire language, and language allows forms of social understanding (and, more broadly, culture) that would otherwise be impossible. Both "language" and "social cognition" are complex constructs, involving many independent cognitive mechanisms, and the comparative approach provides a powerful route to understanding the evolution of such mechanisms. We provide a broad comparative review of mechanisms underlying social intelligence in vertebrates, with the goal of determining which human mechanisms are broadly shared, which have evolved in parallel in other clades, and which, potentially, are uniquely developed in our species. We emphasize the importance of convergent evolution for testing hypotheses about neural mechanisms and their evolution.

Figure 1. Different Levels of Gaze Responsiveness

(A) A macaque monkey is aware that a human experimenter looks in its direction and thus refrains from taking the food. (B) A raven follows the gaze direction of a human experimenter above its head, i.e. it looks up. (C) A raven also follows the gaze of a human experimenter behind a visual barrier by relocating its position. (D) A dog uses the gaze direction of a human experimenter to find food hidden under one of two inverted cups. Dotted arrows indicate gaze direction. Full arrows indicate movement of test subjects.

Figure 2. Cooperative versus Competitive Set-Up in Knower-Guesser Experiments

(A) A chimpanzee sees a human experimenter hiding food while two other humans are present, one actively watching the baiting process, the other one having a bucket on his head. In the subsequent test, both humans offer their help to the chimpanzee by pointing toward a particular container. In such a cooperative set-up, chimpanzees must learn, slowly, to prefer the knowledgeable human who had seen the caching over the guesser whose view was blocked by the bucket. (B) A subordinate chimpanzee (on the right) has the choice to retrieve food that is within view of a dominant conspecific (on the left) or hidden behind a visual barrier. In this competitive set-up, chimpanzees instantly go for the food that cannot be seen by the dominant animal.

Figure 3. Cumulative Cultural Change in Birdsong

The best examples of cumulative cultural change in nonhuman animals come from birdsong. An isolated male songbird, deprived of song input during the critical period, will produce an aberrant “isolate” song. However, if this aberrant song is provided to a second generation of young males, they will learn it and improve upon it, bringing it closer to the wild-type. Repeating this process over generations leads to a song little different from normal wild-type song.

Figure 4. Marmoset Imitation

(A) Common marmosets precisely imitate a conspecific using a peculiar technique to open a food canister. Motion analysis confirmed the high copying fidelity of the observers. (B) The head movement was calculated from the movements of five trace points (blue dots): (1) corner of the mouth, (2) outer corner of the nostril, (3) canthus, (4) corner of the white spot of the forehead, and (5) a corner at the base of the ear-tufts. (C) One example each of the head position of the model, one observer, and one nonobserver in 1/25 s time intervals (red lines indicate head inclination) illustrate the high matching degree of model and observer, but considerable deviation of the nonobserver’s, movement trajectory. (D) The mean discriminant scores for movements of the observers were closer to the mean of the model than to the nonobservers in 99.96% of the cases (Voelkl and Huber, 2007).

Figure 5. Kea Selectivity

Keas were allowed to observe a trained conspecific that demonstrated how to open a large steel box with rewards (toys). The lid of the box could be opened only after three locking devices had been dismantled (a bolt, a split pin, and a screw). The figure shows an observer pulling the metal split pin out of the screw in its first encounter with the box. Observers showed much greater success in opening the locking devices than nonobservers (Huber et al., 2001).

Figure 6. Rational Imitation in Children and Dogs

Both human infants and dogs evaluate the actions of others and decide whether or not to copy them. Children (or dogs) watched a model turn on a light box (or push a bar) by touching its top with her forehead, not her hands (or by pushing it down with a paw, not the mouth). If a model had a blanket wrapped around her body (or a ball in the mouth) during the demonstration (“occupied” condition), only about 20% of observers activated the box with their heads (or pushed the bar with the paw). The majority of the children (or dogs) used the hand (or mouth)—a more efficient way of turning on the lights (or depressing the bar). Perhaps they recognized that the model couldn’t use her hands (or the mouth) and had to use her head (or paw). But when the model performed the task without the blanket (or without the ball) (“free” condition), the majority of a second group of observers opted to copy the model’s head (or paw) movements, as if deciding that if the model did it, then it must be a better approach (Gergely et al., 2002; Range et al., 2007).

Figure 7. A Preliminary Cognitive Phylogeny for Gaze Processing

(A) The widespread occurrence of gaze sensitivity (GS) implies the presence of GS in the LCA of all amniotes. (B) In contrast, the scattered distribution of gaze following (GF) and geometric GF (GGF), based on current knowledge, leaves open the possibility of convergence in birds and mammals, or homologous descent from an early amniote.