The relevant neurobiological mechanisms are explored in this paper in order that the proposed evolutionary scenario should not be seen as teleological. The brain's functional characteristics play a key role in the above triadic interactions. In this paper, a potential evolutionary scenario that led humans to invent successively more complex forms of tools, and eventually to acquire the language faculty, will be proposed based on this dynamic interaction. New brain functions would constitute the basis for further innovation in cognitive functioning and thus further modifications to the ecological niche, providing a feedback loop for ‘triadic niche constructions’. It is possible that ecological changes to habitats have occurred not as a cause of hominin cognitive evolution, but rather as a result of it, with consequent selection pressures acting on the neural basis of behavioural adaptations to the modified environment. Such interactions might have accelerated hominin evolution, which seems remarkably rapid if it was simply the product of natural selection driven by exogenous environmental change. The above three classes of niche have coevolutionary interdependencies. This concept will be extended in this paper to include the ‘cognitive niche’ as a newly acquired class of cognitive capacity, and the ‘neural niche’ as a portion of neural tissue added through expansion of the brain. ‘Niche-construction’ denotes an evolutionary process whereby the activities of organisms modify their habitat, to which in turn the organisms evolve to adapt, thus creating their own ‘ecological niche’ in the environment. Humans have constructed a new ‘niche’ in each of these ecological, cognitive and neural domains. Such new cognitive capacities in turn are an outcome of the dramatic expansion of the human brain and of new functional brain areas. The evolution of various new cognitive capacities, including those underwriting the manufacture and use of tools and the production and comprehension of languages, has enabled these ecological transformations. In the course of human evolution and human history, our ancestors have created new habitats from modified hunter–gatherer environments to agricultural landscapes with villages, and then to modern civilized technological cities. The brain mechanisms that subserve tool use may bridge the gap between gesture and language-the site of such integration seems to be the parietal and extending opercular cortices. We advance a speculative argument about the origins of its neurobiological mechanisms, as an extension (with wider scope) of the evolutionary principles of adaptive function in the animal nervous system. The brain's functional characteristics seem to play a key role in this triadic interaction. Human higher cognitive activity can therefore be viewed holistically as one component in a terrestrial ecosystem. In this way, humans have constructed a novel niche in each of the ecological, cognitive and neural domains, whose interactions accelerated their individual evolution through a process of triadic niche construction. Extended brain functions would have driven rapid and drastic changes in the hominin ecological niche, which in turn demanded further brain resources to adapt to it. The dramatic expansion of the brain that accompanied additions of new functional areas would have supported such continuous evolution. Hominin evolution has involved a continuous process of addition of new kinds of cognitive capacity, including those relating to manufacture and use of tools and to the establishment of linguistic faculties.
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