Neencephalization, hominization and behaviour

Abstract Neencephalization, i.e. enlargement of the neocortex of the brain, became representative of the higher mammals, including the primates, during the Tertiary. Consequently, the number of embryos per gestation became limited to one per gestation in nearly all cases. The intra-uterine time-span increased at the same time and also the ontogeny. As an effect of this, childhood and youth until adulthood became longer and sexual maturation was retarded to the same extent. Consequently the duration of one generation increased, and so, too, did the time-span that elapsed before a new combination of haploid gene-sets of the partners could (in view of the high death-rate before adulthood) realize the possibility of self reproduction. From paleodemographical data we know that this “effective duration of one generation” needed for Homo sapiens sapiens was about 35 years. This means, that for the process of evolution the number of new gene-combinations offered in the sequence of generations was very much lower, and at the same time the length of each generation became greater. As a significant compensation we find as an effect of neencephalization the ability to learn, realized through learned behaviour. Thus, the remarkably lower number of offspring could in fact “better” survive, using vertically transmitted experience in socialized groups instead of high losses through only personal trial and error with innate modes of behaviour. The possible tempo of evolutive processes must consequently have became slower, if in addition we consider the fact, that a smaller number of realizable mutations needed more time to became through selection representative of a taxon by distribution over slow gene-flow. Add to this the fact that most of our characteristics are directed multifactorially and pleiotropically. Hominid fossils represent thus in every case only local sectors of small populations. Their combinations of morphological traits represent in most cases limited sections. In view of this we must be careful not to confuse the issue by denominating morpho= as bio-taxa. In every case, we have to calculate for the human phase only about 3000 generation-sequences in 100,000 years. This indicates for the humane phase the time needed to reach the full state of a “species” with fully developed physiologically effective barriers separating them from related preceding or following taxa, must be calculated as being relatively large.