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Language is both a social and biological phenomenon. The capacity to acquire and use it is a unique and distinctive trait that evolved in only one species on Earth. Its complexity and organization are like nothing else in biology, and yet it is also unlike any intentionally designed social convention. Short of appealing to divine intervention or miraculous accident, we must look to some variant of natural selection to explain it. By paying attention to the way Darwin’s concept of natural selection can be generalized to other systems, and how variants on this process operate at different interdependent levels of organism function, explaining the complexity of language and the language adaptation can be made more tractable.

Darwin’s theory of natural selection is based on three widely acceptable characteristics of organism reproduction. In the early winter of 1838, after reading Thomas Malthus’ “Essay on Population,” Charles Darwin wrote the following lines in his E Notebook: “Three principles will account for all: (1) Grandchildren like grandfathers; (2) Tendency to small change … especially with physical change; (3) Great fertility in proportion to support of parents” (Darwin, 1838, p. 58).

In the most general terms, these correspond to duplication-multiplication, spontaneous variation from the original, and the surfeit of reproduction that will inevitably reduce this variety via competition for scare resources. Darwin’s final refinement was to recognize that, given inevitable culling, the conditions of survival (and particularly, reproduction) would differentially reduce this variety in a way that favored variant traits best suited for that context—adaptation. Darwin recognized that irrespective of the mechanisms involved, if these conditions are present, a lineage will tend to become adapted to local conditions if given sufficient time and generations. This was a remarkably simple recipe for biological change, and yet its implications were enormous and counterintuitive. As one critic of On the Origin of Species (Darwin, 1859) was to write: “In the theory with which we have to deal, Absolute Ignorance is the artificer; so that we may enunciate as the fundamental principle of the whole system, that, in order to make a perfect and beautiful machine, it is not requisite to know how to make it” (MacKenzie, 1868, p. 217).

Adaptation is the natural counterpart to functional design, but the idea that exquisite biological design might be achieved in the absence of any information about the context of use seemed absurd. Deeply ingrained intuitions, gained through the difficult experience of designing and constructing even simple artifacts and machines, made it unquestionable that only considerable planning and knowledge about the relevant properties of the materials and tasks involved could yield reliable functional outcomes. Moreover, the difficulties encountered multiply geometrically with increasing complexity because of the way that changing one component

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