language link + large excerpt

Evolution of Symbolic Language

Some propose that language appeared recently, and suddenly, due to some marvelous mutations that transformed "dumb brutes" into articulate speakers. If language is a recent feature of human social interaction — arising, say, 100,000 years ago as an evolutionary afterthought — then it would have had little opportunity to impose selection pressures; hence language abilities would be expected to have been inserted unsystematically into an otherwise typical (if enlarged) ape brain. If so, they should be poorly integrated with other cognitive functions, relatively fragile if faced with impoverished learning contexts, and susceptible to catastrophic breakdown as a result of genetic defects.

None of this seems to be the case.

If, instead, language has been around for a good deal of our evolutionary past, say a million years or so, the demands of language would have had time to affect brain evolution more broadly. A large network of subtle gene changes and neurological adjustments would be involved, resulting in a well-integrated and robust neurological function. Indeed, there is ample evidence to suggest that language is remarkably well-integrated into almost every aspect of our cognitive and social lives, that it utilizes a significant fraction of the forebrain, and is acquired robustly under even quite difficult social circumstances and neurological impairment. It is far from fragile.

If language-like communication has been a long-time feature of hominid evolution, then languages themselves must also have a long history. Since the language one learns must be passed from generation to generation, the more learnable its structures, and the better its fit to human limitations, the more effective its reproduction in each generation. Hence languages and brains are expected to have evolved in tandem. That said, brain evolution is a ponderously slow and unyielding process compared with the more facile evolution of languages, so we should expect that languages are more modified for brains than are brains for languages.
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Language is in effect an emergent function, not some prior function that just required fine-tuning. Our inherited ("instinctive") vocalizations, such as laughter, shrieks of fright, and cries of anguish, are under localized, mostly subcortical, neurological control, as are analogous instinctive vocalizations in other animals. By contrast, language depends on a widely dispersed constellation of cortical systems. Each system is also found in other primate brains, where they engage in other functions; their collective recruitment for language was apparently driven by the fact that their previously evolved functions overlapped with particular processing demands necessitated by language. Old structures came to perform unprecedented new tricks.
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This story is relevant to the human because a number of features of human language adaptation also appear to involve a relaxation of innate constraints. Probably the clearest evidence for this is infant babbling, an unprecedented tendency to freely play with vocal sound production, with minimal innate constraint on what sound can follow what (save physical constraints on vocal sound generation). Babbling occurs in contexts of low arousal, whereas laughter, sobbing, and shrieking are each produced in high-arousal states with specific contextual associations. This reduction of emotional and contextual constraint on sound production opens the door for numerous other influences to play a role, allowing many more brain systems to participate in vocal behavior, including socially acquired auditory experience. In fact, such freedom from constraint is an essential precondition for being able to correlate learned vocal behaviors with the wide diversity of objects, events, properties, and relationships that language is capable of referring to. Hence an evolutionary de-differentiation process, while clearly not the whole story, may be a part of the story for symbolic language evolution.