Application of the heterochrony framework to the study of behavior and cognition

Abstract

Heterochrony, or the evolution of ontogeny, has been well studied in embryology and skeletal development, providing insight into morphological and genetic mechanisms of evolution.1-5 However, heterochronic studies of behavior and cognition lag behind in comparison. In a recent study we investigated the ontogeny of social behavior and cognition in humans' closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). These two species are estimated to have had a chimpanzeelike common ancestor between 0.86 and 1.8 mya.6,7 Bonobos have been argued to exhibit morphological indications of paedomorphism relative to chimpanzees, especially in the cranium, and to exhibit paedomorphic behavior as adults.6-11 We found that bonobos exhibit developmental delays relative to chimpanzees in several aspects of their social behavior and cognition. Here, we describe how placing these results in the framework of heterochrony contributes to understanding behavioral and cognitive differences between adults of these two species and to our knowledge of hominid evolution in general.

Keywords: behavior; bonobo; chimpanzee; cognition; evolution; heterochrony; ontogeny.

Figure 1

Depictions of the patterns found in our recent study in comparison to models of paedomorphosis. Bonobos appear to exhibit neoteny or rate hypomorphosis in their ontogeny of intolerant behavior, while in their patterns of social inhibition across two tasks they appear to exhibit postformation, the process found to create paedomorphosis in aspects of the bonobo cranium.