To confirm the limits and regularity of among-group variations in the craniofacial morphology of Homo sapiens sapiens, and, if possible, to determine some of the causes for the regularity, data of craniofacial measurements and environmental variables were collected for many Homo s. s. populations of the Neolithic to modern times in various regions of the world (687 male and 340 female samples).

    The minimum and maximum values in the among-group variation of each craniofacial measurement were simply explored using the data collected.  In a within-group multivariate space, it was found that the PC scores for the mean vectors of craniofacial measurements in almost all the samples were located within the ±2 SD ranges of the within-group PC scores based on a single sample.  This finding suggests some complicated system or factors controlling the coordination between substructures of the skull (or the body).

    The PCAs of among-group correlations between craniofacial measurements clearly indicate the existence of significant common factors, namely, the robust evidence for regularity in the inter-population variations of craniofacial morphology.  This means that our craniofacial morphology has not been formed only by chance but, in part, determined by some inevitable controlling factors in the human evolutionary processes.

    In the PCAs of among-group correlations between craniofacial measurements and environmental variables, it was found that cranial breadth, upper facial height, bizygomatic breadth, and nasal height tended to be larger in colder regions of higher latitudes; that basi-bregmatic height and nasal breadth tended to be larger and, inversely, minimum frontal breadth tended to be smaller in the regions more distant from Ethiopia and of lower latitudes where average precipitation was higher and average temperature was also relatively high; and that cranial length and cranial base length tended to be larger in ancient times (for the past 7,000 years).  In the present study, these findings were interpreted as the results of evolutionary adaptation to our natural and sociocultural environments.

    As regards brachycephalization or dolichocephaliztion, it was considered a phenomenon caused by the differential adaptations and/or acclimatizations to our diverse natural and sociocultural environments and by the difference in the way of connecting with other characters between cranial length and breadth.

    Path analyses indicated the existence of unknown factors making a relatively large contribution to each craniofacial measurement.  This is not inconsistent with the results of among-group PCAs.

    In conclusion, the purposes of the present study were partly achieved.  The limits and regularity of among-group variations in craniofacial measurements were confirmed; temperature was reconfirmed in a global scale to be a very important cause for our adaptaion to environment; and precipitation and humidity were also suggested to be important causes.  But we must still collect more data of various environmental factors, natural and artificial (cultural, social, etc.) and ancient and modern, to clarify the causality for the formation process of our morphology.