Evolutionary Developmental Biology and Human Language Evolution: Constraints on Adaptation

Abstract

A tension has long existed between those biologists who emphasize the importance of adaptation by natural selection and those who highlight the role of phylogenetic and developmental constraints on organismal form and function. This contrast has been particularly noticeable in recent debates concerning the evolution of human language. Darwin himself acknowledged the existence and importance of both of these, and a long line of biologists have followed him in seeing, in the concept of “descent with modification”, a framework naturally able to incorporate both adaptation and constraint. Today, the integrated perspective of modern evolutionary developmental biology (“evo-devo”) allows a more subtle and pluralistic approach to these traditional questions, and has provided several examples where the traditional notion of “constraint” can be cashed out in specific, mechanistic terms. This integrated viewpoint is particularly relevant to the evolution of the multiple mechanisms underlying human language, because of the short time available for novel aspects of these mechanisms to evolve and be optimized. Comparative data indicate that many cognitive aspects of human language predate humans, suggesting that pre-adaptation and exaptation have played important roles in language evolution. Thus, substantial components of what many linguists call “Universal Grammar” predate language itself. However, at least some of these older mechanisms have been combined in ways that generate true novelty. I suggest that we can insightfully exploit major steps forward in our understanding of evolution and development, to gain a richer understanding of the principles that underlie human language evolution.

Neanderthal language revisited: not only us

“…Almost no-one doubts AMH had language 60 kya just before the great diaspora, since all branches of humankind have language, but how far back should we project it? The evolution of language involved very probably a complex interplay between exaptation, reorganization, phenotypic plasticity, adaptation and cultural evolution, touching many components and processes, requiring tens or hundreds of thousands of years and proceeding at highly variable rates [1,[71][72][73]. The 'externalization' of language and its neural underpinnings, far from being trivial, is, in our view, one of the clearest clues to its long gestation.…”

Empirical approaches to the study of language evolution

“…These mechanisms were already in place when the few specific changes required for language evolved. As discussed below, all of these characteristics were preadaptations to language: mechanisms that are used in language, but did not specifically evolve for language (Fitch, 2012).…”

A comparative neurological approach to emotional expressions in primate vocalizations

“…Whether the human larynx is truly different from that of other animals -particularly great apesand whether this has any direct consequences for the uniqueness of human speech is under debate (Ankel-Simons, 2007;Fitch, 2012); thus, we assume here that the basic mechanisms of vocal production are similar in all primates, including humans (Ghazanfar and Rendall, 2008). Processes in the larynx and supralaryngeal vocal tract are controlled by several nuclei located in the pons and medulla that project through subcortical regions (e.g.…”