We may well regard the high intelligence and the ambition of the European races as an adaptation to the competition and crowding arising in a life largely devoted to barter and commerce in a continent so well adapted by nature, thru its diversified shore-line, for trade.
Each race of man that has long persisted in a distinct environment has gained, by preservation of useful mutations, certain adaptation to that environment. The useful phenotypical adaptations have enabled their possessors to survive and the genotype that produced them continues the characters of the race. Sexual selection tends to maintain the especial standard, or norm, in each place. The black negro of Africa prefers his own color and his own form of lips and nose.
In the mixture of the races which is now taking place there are combinations of genotypic conditions which sometimes lead to disharmony in the phenotype. Such disharmony may be illustrated by the case of a hybrid between the Leghorn fowl (which has the instinct of laying continuously and never going broody) with a Plymouth Rock (which periodically goes broody, hatches its chicks and rears them to maturity). The hybrid in question is white, like the Leghorn. Such a hybrid will lay a clutch of eggs and will then go broody. It may even hatch out chicks and tend them for a day or two but will then begin to lay again and neglect the chicks so that they will all die. Such a disharmony of instincts is thus found in a hybrid, so that it is less effective than a bird that never goes broody or one which has instinct the[sic] of completing its maternal functions.
It is probable that even on the morphological side disharmonies may arise from conflict of developmental tendencies. Thus in America we have a union of some races that are characterized by large teeth,