Thursday, September 24, 2009

Human Evolution and The Slow Development of Symbolic Thought

Fascinating FREE article at PLOS arguing that in human evolution symbolic thought evolved much later than the biological substrate that would have allowed it. I have no idea how generally accepted this is, but it's a fascinating idea with maybe some implications for human learning and theories of discourse.
Evidently, then, “becoming human” took place in two separate stages. First, the distinctive modern human morphology became established, very clearly in Africa, and probably shortly after 200 Ka. This event involved a radical departure from the primitive Homo body form. Only ca. 100 Ka later, again in Africa, and in a Middle Stone Age industrial context, did modern symbolic behaviors begin to be expressed, underwritten by a new capacity that had most plausibly been present but unexploited in the first anatomical H. sapiens. In evolutionary terms this disconnect was entirely routine, for every new behavior has to be permitted by a structure that already exists: Birds, for example, had feathers for millions of years before coopting them for flight, and tetrapods acquired their limbs in an aquatic context (52).

Symbolic reasoning appears to be qualitatively different from all other forms of cognition, including its own immediate precursor. Its neural substrate continues to be strenuously debated (53, 54); but, whatever it was, that structural innovation was most plausibly acquired as part and parcel of the radical biological reorganization that gave birth to H. sapiens as an anatomically distinctive entity. In which case (like those feathers and limbs) it remained unexploited, at least in the cognitive context, for a very substantial length of time, until its new use was “discovered” by its possessor. How this discovery was made remains a matter for conjecture, but a leading candidate for the necessarily cultural stimulus to symbolic processing of information is the invention of language (55). Language is perhaps the ultimate symbolic activity; and, in contrast to theory of mind, the other leading candidate for the role of releaser (56), it has the advantage of being a communal rather than an internalized attribute. The ability to use language depended, of course, on the presence of the vocal structures required to produce speech; but clearly these had already been exaptively acquired by the earliest anatomical H. sapiens.

Current evidence thus indicates that H. sapiens as we know it today had a dual origin: first as an anatomical entity, and only subsequently as a cognitive one. The clear signal of both the fossil and archaeological records is that both innovations occurred in Africa, from which the first fully modern humans expanded relatively recently to populate the rest of the world.

h/t four stone hearth (them there anthropologists are pretty damned organized online) at Afarensis via our old friend Neuroanthropology

1 comment:

A. G. said...

Fascinating, Aaron, I have shared widely with neuro ed folks here at Purdue.