It seems probable that man was evolved from his prehuman ancestry as a single stock, probably a stock somewhat widely distributed in the heart of the Eurasian continent, or possibly in Africa according to the recent view of some authors, or in the area which is now the Indian Ocean. If this be true, it follows that the differentiation of the mental and physical qualities of the principal human races, the differentiation of the white and black and yellow and brown races, as well as of the chief subraces, such as the Semitic, the races of Europe--the _Homo Europaeus_, _Alpinus_ and _Mediterraneus_--was the work of the immensely prolonged prehistoric period. For these races and subraces, as we now know them, seem to have been in existence and to have had recognisably and substantially the same leading qualities, both mental and physical, that they now have, before the beginning of the historic period.
The racial differentiation during the prehistoric period must have been much greater than during the historic period; and this was not only because the former period was immensely longer, but also because, in all probability, the rate of racial change has been on the whole slower in the historic period.
The differentiation of racial types in the prehistoric period must have been in the main the work of differences of physical environment, operating directly by way of selection, by way of the adaptation of each race to its environment through the extermination of the strains least suited to exist under those physical conditions. But this process, this direct moulding of racial types by physical environment, must have been well nigh arrested as soon as nations began to form. For the formation of nations implies the beginning of civilisation; and civilisation very largely consists in the capacity of a people to subdue their physical environment, or at least to adapt the physical environment to men's needs to a degree that renders them far less the sport of it than was primitive man; it consists, in short, in replacing man's natural environment by an artificial environment largely of his own choice and creation.
In a second and perhaps even more important way, the formation of nations with the development of civilisation modified and weakened the moulding influence of the physical environment; namely, it introduced social co-operation in an ever increasing degree, so that the perpetual struggle of individuals and of small family groups with one another and with nature was replaced by a co-operative struggle of large communities against the physical environment and with one another. And in this process those members of each community who, by reason of weakness, general incapacity, or other peculiarity, would have been liable to be eliminated under primitive conditions became shielded in an ever increasing degree by the powers of the stronger and more capable against the selective power of nature and against individual human forces. And, although within the community the rivalry of individuals and families still went on, it was no longer so much a direct struggle for existence, but rather became more and more a struggle for position in the social scale; and failure in the struggle no longer necessarily meant death, or even incapacity to leave an average number of descendants. That is to say, primitive man's struggle for existence against the forces of nature and against his fellow men, which made for racial evolution and differentiation through survival of those fittest to cope with various environments, tended to be replaced by a struggle which no longer made for racial evolution towards a higher type, and which may even have made for race-deterioration, at the same time that civilisation and national organisation continued to progress.