Culture, symbols, and human brain evolution: A synthesis

Abstract

1. The brain has always played an important role in human evolution, but if brain size alone is the single neural variable considered, we cannot understand either the richness, complexity, or challenges inherent in a theory of human evolution. The brain is not simply a terminal product in mosaic human evolution. 2. Brain size is only one phenotypic “window”, as it were, which allows the investigation of the role of the brain in human evolution. Of equal, if not more importance, are other phenotypic “windows”, on the brain such as its organizational (meaning the quantitative relationships among its parts) and its hierarchical development. This latter aspect refers to the species specific time-course of developmental, maturational, and social interactional and trans-actional patterns that shape the brain through natural selection. 3. One aspect of brain size increase during human evolution relates to the geometric changes that took place in the central cortex. That is, one of the manifestations of increased cell size, decreased neuron density, increased dendritic branching, and increased glial/neural ratios, was an increase in absolute brain size. These aspects, albeit imperfectly, reflect one manifestation of neural complexity. Greater relative brain size, reorganization of cerebral tissues (e.g., the ratio of “association” cortex to primary visual cortex), hemispheric lateralization, and cognitive competence in symbolling and visuo-spatial integration, represent another set of neural evolutionary changes in Homo. 4. While all animals may “learm” and perhaps even have “traditions,” no other being organizes its experiences in arbitrary symbol systems imposed by social groups, where there are non-iconic (arbitrary) relationships between the symbol(s) and referent. The power of this “new” language, integrated with “natural” neural “languages” is enormous, and escalates the complexity of social and material environments to which the human animal attends. Environments can be created through productivity and displacement. Culture is a human domain, if any definition of culture is to have meaning relative to the unique behavioral and cognitive patternings that typify the human being. It is impossible to understand the unique evolutionary past of our species without holistically integrating behavioral (cultural) and neural complexity, and the cognitive basis for both. 5. Stone tool-making patterns from the prehistoric past should be viewed as indices or clues to the totality of complex social behavior in the past, rather than as targets for natural selection in the limited sense of tools as extrasomatic adaptations. Camping, living, manufacturing and butchering sites should be similarly viewed. The challenge is to try to understand these activities as clues to how social experience was organized and transmitted. In this framework, such activities reflect cultural and cognitive complexity and not cultural evolution per se. 6. Prolonged dependency and growth periods must be integrated with the evolutionary changes in neural and cultural complexity. It is at this level that more molecular genetic changes, i.e., regulatory RNA, can be related to the more molar anthropologically-oriented evidence of the evolutionary past. Such changes in growth and dependency were probably dependent upon the development of affectional relationships between the sexes and members of social groups, which minimally increased the duration, if not intensity, of social, cooperative, nurturant relationships. Changes in sexual dimorphism, for example, which can only be inferred, are clues to those social relationships that set brain and behavioral complexity into a mutually-causal and interdependent evolutionary schema. The changes discussed above are the “initial kick” in that schema.