Zur Evolution des menschlichen Kopfes

Abstract:

In the evolution of the human head a Shift in complexity takes place. Complexity is predorninately reduced in the jaw region (distally), in which the organism comes into direct contact with the environment through nutrition. Proxirnally, in the brain, besides the degradation processes present, complexity is predominately increased. The evolution of language with its organs of speech occupies an intermediate mediating role and forms a gradient with predominately increasing complexity proximal and decreasing complexity distal. The reduction of complexity in the jaw region takes place through paedomorphosis (neoteny and postdisplacement), the increase of complexity of the brain through peramorphosis (sequential hypermorphosis and predisplacement). Plasticity — along with other factors — plays a role in both processes. Both, the jaw region and the brain, react highly plastically to their use. Thus, the jaw region is relieved through cultural achievements like tool use, whereas the brain is further stimulated by them, which contributes to its increasing structure. It is more likely that the genes follow the plastic changes than that they are the leaders in the evolution of novelties. Because of the high plasticity at the biological level, and through the development of tools, language and a social way of living, humans contribute to their own evolution.

In the course of evolution, humans, with their neotenic jaw apparatus, become increasingly free from their environment. With the culture of tools and the use of fire, they become more and more independent of single food sources. Simultaneously, childhood and youth was prolonged in connection with the increasing protection by parental care. This was correlatcd with a longer period of brain growth and an increase in learning processes. Thus, innate and instinctive behaviour could be largcly replaced by longer and more intensive learning processes and individuals could acquire greater flexibility and creativity than their ancestors. I-Iumans became more autonomous. In the evolution of the head, precisely its childlikc qualities — the learning capacity, the high plasticity of the brain, the high brain growth and the comparatively small jaw part — are increased through an ontogenetically early onset of peramorphosis in the brain, and preserved by a predominantly late paedomorphosis of the chewing apparatus. Th us, in the head, the increase of childlike features contrihutes to human autonomy, whereas in the lower limbs it is the increase in adult qualities.