The extended evolutionary synthesis: its structure, assumptions and predictions

Abstract

Scientific activities take place within the structured sets of ideas and assumptions that define a field and its practices. The conceptual framework of evolutionary biology emerged with the Modern Synthesis in the early twentieth century and has since expanded into a highly successful research program to explore the processes of diversification and adaptation. Nonetheless, the ability of that framework satisfactorily to accommodate the rapid advances in developmental biology, genomics and ecology has been questioned. We review some of these arguments, focusing on literatures (evo-devo, developmental plasticity, inclusive inheritance and niche construction) whose implications for evolution can be interpreted in two ways-one that preserves the internal structure of contemporary evolutionary theory and one that points towards an alternative conceptual framework. The latter, which we label the 'extended evolutionary synthesis' (EES), retains the fundaments of evolutionary theory, but differs in its emphasis on the role of constructive processes in development and evolution, and reciprocal portrayals of causation. In the EES, developmental processes, operating through developmental bias, inclusive inheritance and niche construction, share responsibility for the direction and rate of evolution, the origin of character variation and organism-environment complementarity. We spell out the structure, core assumptions and novel predictions of the EES, and show how it can be deployed to stimulate and advance research in those fields that study or use evolutionary biology.

Evolutionary neuroscience of cumulative culture

“…That nonspecific selection for increased brain size in the human lineage might have indirectly driven increased plasticity is suggested by evidence of low heritability for cortical morphology (sulcal dimensions) vs. overall brain size in humans, a pattern that contrasts with high heritability of both in chimpanzees (67). In any case, the human association cortex appears particularly sensitive to environmental and behavioral influences, providing a potent evolutionary feedback mechanism between organism and environment, which the EES refers to as reciprocal causation (56).…”

“…This behavioral continuum maps roughly onto the differing contributions of dorsal and ventral processing streams in the primate brain. (56). Any viable evolutionary account of cumulative culture must address these dynamics.…”

The evolution of cognitive mechanisms in response to cultural innovations

“…The components that may evolve over generations are the parameters of the learning and data-acquisition mechanisms that construct the network through interaction with the environment, and whose coordinated action, as we show below, is critical for building the network appropriately. [This coevolution is very much in the spirit of the notions of constructive development and reciprocal causation in the recently proposed "extended evolutionary synthesis" (89). ]…”

Evolution of long-term coloration trends with biochemically unstable ingredients

“…Darwin considered this question to be central to his theory of evolution, because it would provide a crucial insight into the relationship between inheritance and natural selection [1], and between the developmental stability of complex phenotypes and their ability to accommodate and integrate novel inputs [2 -4]. There are several insightful conceptual resolutions of this question [5][6][7][8][9][10], but empirical tests are rare because they require investigation of evolutionary trajectories where an environmentally contingent trait gets reliably incorporated into the phenotype and stabilized over evolutionary timescales.…”