By Paul Mason & Daniel Lende
Terrence Deacon, professor of anthropology at Berkeley, has a 2010 paper in the Proceedings of the National Academy of Sciences, A Role for Relaxed Selection in the Evolution of the Language Capacity. It is part of an outstanding special PNAS issue “In the Light of Evolution,” which includes papers from Bernard Wood, Nina Jablonski, Kristen Hawkes, Richerson & Boyd, Tooby & Cosmides, and Steven Pinker (all full access!).
Deacon has a long-term interest in building explanations of language that combine evolutionary process with neurobiological analysis, most prominently in his excellent book The Symbolic Species. This paper focuses on the evolutionary side:
A common feature [of these evolutionary explanations] is an interplay between processes of stabilizing selection and processes of relaxed selection at different levels of organism function. These may play important roles in the many levels of evolutionary process contributing to language. Surprisingly, the relaxation of selection at the organism level may have been a source of many complex synergistic features of the human language capacity, and may help explain why so much language information is “inherited” socially.
You can hear Deacon lecture on the topic in Whence Language?, an audio file coupled to a PowerPoint, where he outlines his overall approach.
In the PNAS paper, Deacon describes natural selection as characterized by replication, variation and differential preservation, and hypothesizes that the social history of language should exhibit evolvability due to redundancy, dedifferentiation (degeneracy), and functional interdependency.
Deacon argues that as a system like language becomes more highly complex, it simultaneously becomes more functionally degraded by structural variation. In complex systems, the tight coupling of structure and function can be loosened, as selection maintains the overall function of the system even as processes like mutation introduce variation into the different components of the working system.
Complex systems also have functional redundancy, which allows for a relaxation of selective processes that provides the space for replicators to incrementally deviate from their antecedent function. The relaxation of selection helps favor the preservation of structural variants, and thus functional dedifferentiation.
According to Deacon’s reasoning, the involvement of neural circuitry and the increased importance of social transmission in the determination of vocalization could be a product of this functional dedifferentiation. The distribution of function onto an array of components effectively offloads a significant degree of genetic control onto epigenetic processes. The subsequent openness to experiential modification provides a greater degree of freedom for the influence of social transmission and the intersubjective exploration and experimentation with vocabulary and grammar.
In other words, the structural aspects of language, as they grow more complex and inter-linked, relax the process of selection, with its natural tendency to hone particular functional adaptations. In turn, this opens up new evolutionary spaces for the evolution of complexity. In the case of language, this relaxed selection opens up language to greater epigenetic influence and social and experiential learning.
It is a complicated but compelling argument, so please do check out the full paper (pdf), A role for relaxed selection in the evolution of the language capacity.
Deacon’s lecture Whence Language?
Deacon also has a piece over at On the Human, Rethinking the natural selection of human language.