Hominid cranial capacity change through time: a darwinian process

Abstract

The course of change in hominid cranial capacity through time is described for the period 3200-15 ky B P. Both analysis of variance and fitting of regression curves performed on a sample of 144 specimens point towards a smooth gradual change at an increasing rate. Residual variances around empirical and theoretical lines of regression are smaller than the total intraspecific variance in modernH sapiens testifying as to the goodness of fit. It is postulated that the gradual nature of the evolutionary process results from the operation of a typical darwinian mechanism of directional selection. Rates of selection themselves undergo increase as a result of self-amplifying nature of hominid evolution resulting from positive feedbacks between evolving elements of the bio-cultural complex. Therefore the theoretical regression is of a doubly exponential form: exponential increase of cranial capacity with time at rates that themselves increase exponentially. As the change is gradual and variance around the line of regression does not exceed that observed within a single species from the viewpoint of cranial capacity hominid evolution may be described as a continuous series of ill-separated chronospecies.