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Three Dimensions of Development in the History of the Human Species: Neuro-Cognitive, Social, and Physical

Complex behaviors are generally assumed to develop incrementally during the course of the evolution of an organism, especially when they involve learning. Such behaviors are too complex to develop simply by means of a single simple mutation and subsequent selection for a single resulting gene (as Noam Chomsky has claimed but neuroscientists, and now other scientists using empirical evidence of various sorts, reject).

In the case of human language, the behavior is so complex that there is a whole range of skills and capacities involved, from articulatory abilities (e.g. fine, coordinated motor routines for the pharynx, larynx and articulators), to social abilities to negotiate turn-taking and sharing of attention to external object, to conceptual abilities to categorize the world in useful ways and draw inferences about cause and effect which allow for correct predictions about what will happen if you do x,y,z.

We can usefully distinguish three dimensions of development for the various skills and capacities that appeared over the course of hominid evolution and ultimately formed the necessary underpinnings for human language. These types of development are: Neuro-cognitive, social, and physical.

Note that "development" here means evolutionary development, i.e change over time in an evolving branch of the primate family. Psychologists most often use the term "development" and "developmental" to refer to changes in an organism from birth to adulthood. Evolutionary development is called phylogenetic development and development of organisms in their lifetime is called ontogenetic development. This summary is about phylogenetic development, although ontogeny is also important in the history of species.

As a caveat, it must be remembered that the three dimensions are not strictly divisible from one another. For one thing, all of the social and physical developments that were needed for language must have some neurological and cognitive correlates; we can't have the social and physical parts without the brain structures to support them. For example, it would not be possible for a modified body part such as the modern larynx, or a new set of tongue muscles, to develop without a part of the cortex also developing, or even coming to be devoted to controlling the body part.

Conversely, it does seem logically and practically possible for complex organisms to develop potential neuro-cognitive skills that do not necessarily have social or physical correlates. This kind of situation is illustrated by some of the cognitive capacities discovered in great apes that are apparently 'unused' in the wild and do not have social functions or adapted physical structures to go with them, e.g. learning some use of symbols (arbitrary form-meaning mappings) in a laboratory context.

I will use the term physical below to refer to physical structures OUTSIDE the brain, since the heading neuro-cognitive necessarily includes not only cognitive/representational, but also physical brain structures.

Questions that are implied by these developments include: at what point in the hominid line did each capacity or skill begin to develop, and at what point did it reach something close to or identical to its modern human correlate? What was the sequence of development of each skill? How does it relate to other skills in the list? Are there some skills that inexorably lead to others, or provide the potential for other skills to "piggyback" on?

More questions: Which pre-human species, if any, show evidence of having had certain of these capacities, and if so, which? Which are the most recent developments? Are there any developments we would want to place in "modern" history, i.e. in the period AFTER the first Homo sapiens sapiens appeared? How did Homo sapiens neanderthalensis compare to Homo sapiens sapiens in respect to these capacities and associated behaviors?

Neuro-Cognitive development includes the following capacities:

Social development includes:

Physical development includes: