Adaptive vs exaptive in the evolution of human language

Evolutionary Biology Meeting, MarseillesThe poster was presented by Irene Berra.

Human articulate language doesn’t involve clearly distinguishable structures and substructures but shows distributed functions. Clues coming from brain comparative studies and neuroimaging point out that cortical structures and connections have been re-functionalized during the evolution of primates and hominids, due to their plasticity and learning capacity. But also the expression of FoxP2 in basal ganglia is involved in vocal and sequential learning. However, neither vocal-learning mammals (whales, dolphins and bats) nor song-learning birds share the human amino acid substitutions (Webb and Zhang, J. Hered., 96, 2005). Language evolution is likely to be a recruitment, with slight modifications, of pre-existing genetic cascades that have other regulatory functions. An exaptive hypothesis has been proposed for acoustic communication during water-to-land transition, as in the case of limbs. Comparative analyses within living species are being conducted to test this hypothesis (Polgar et al., PLoS ONE, 6, 2011) and these may be cases of convergent exaptation. The term was introduced by Gould and Vrba (Paleobiology, 8, 1982) and was blamed of non-operationalizability. Our view (Pievani & Serrelli, Journal of Anthropological Sciences, 89, 2011) is that exaptive hypotheses can be operationalized and improved, and recent research in language evolution offers a good example. We should, e.g., distinguish theories of neural reuse, recycling and re-functionalization (Anderson, Behav. Brain Sciences, 33, 2010) from exaptation when they concern developmental rather than evolutionary processes. Aside from neurobiological studies of language, the exaptationist account is still too speculative (e.g. in anthropology). Enlarging the phylogenetic context, improving technology to identify structures, and attempting the reconstruction of environmental settings to match fitness utility help the historical comprehension of the series of etho-ecological functions of language.

The Evolutionary Biology Meeting at Marseilles is an annual congress which has gathered high level experts in evolutionary biology since its creation in 1997. If the congress was initially a local meeting, it quickly gained an important weight in the scientific life. Indeed, whereas the number of participants has been increasing, the geographical origin of the researchers has been diversifying and widening year by year. Today, the Evolutionary Biology Meeting at Marseilles has reached a worldwide dimension and plays a paramount role in the international scientific life: allowing the gathering of high level specialists, it encourages the exchange of ideas and stimulates the works of the researchers all through the world.

Look for it in the Publications page (with additional links):

Berra I, Pievani T, Serrelli E (2012). How to test adaptive vs exaptive evolutionary hypotheses: the case of human language. Poster at 16th Evolutionary Biology Meeting, Marseilles, France, September 18-21. []

University of Sydney HPS Research Seminar Series

For 80 years now, a famous and influent picture have been around in evolutionary biology: it is the adaptive landscape, a hilly or rugged surface with peaks and valleys onto which combinations of traits are mapped, the elevation representing the fitness value of these combinations. As a communication and heuristic tool, the adaptive landscape well conveyed several ideas, e.g., adaptation seen as peak climbing. It also set research questions, e.g., how can a population cross a low-fitness valley.
In the mid 1990s, with a certain non-chalance, Princeton mathematician and population geneticist Sergey Gavrilets began to propose an idea which soon several evolutionists regarded as potentially explosive. Gavrilet’s “holey landscapes” were about fitness distribution in the genotype space of a population with realistic number of loci and alleles: backed by newly introduced mathematical methods and empirical evidence, they depicted fitness distribution by means of flat or nearly-flat surfaces drilled with large holes.
The explicit reference and, at the same time, the striking differences between holey landscapes and the adaptive landscape fueled a reflection on crucial themes like the role of adaptation, the extent of neutralism, the meaning of speciation, and even the possibility of non-gradual evolution. Reconsiderations and revisions of the history of adaptive landscapes, since its first introduction by Sewall Wright in 1932, flourished. More deeply, holey landscapes are offering an occasion of rethinking the nature of evolutionary biology as a scientific enterprise.

Look for it in the Talks page (with additional links):

2012, Sep 17 (h.6-8 PM) – Unit for the History and Philosophy of Science, HPS Research Seminar Series Semester Two, University of Sydney, Faculty of Science: Holey landscapes and rethinking evolutionary biology. Seminar.