The law of hybridity, which has been so strongly urged against the unity of the race, has proved an argument in favor. The offspring of birds as much alike as the domestic goose and the large Muscovy duck will not propagate their species. Mules cannot perpetuate their kind. The different varieties of the horse, such as the little black Shetland pony and the tall white Arabian, will not only breed together but these hybrids will continue to perpetuate their kind, thereby proving their identity of species. The same may be said of the cross between the most perfect and the lowest type of mankind. If some of these mixtures die out in a few generations, it is not owing to their hybridity, but to the plain violation of natural laws. When the contracting parties to a marriage are of the same constitution, there will be no issue; if the constitutions, or rather, temperaments, are in substance too nearly the same, the issue, if any, will be either still-born, or die very soon after birth; if the contracting parties shall have an adjunctive element, the issue will be short-lived, although they may arrive at the years of maturity.[120] These laws apply to both the mixed and the unmixed types of mankind. The close affinity of all the races, their subjection to the same general laws, their capacity for mental and moral improvement, and the virtual unity of their languages lead to the conclusion that one birth-place was common to all. If that place be Central Asia, or any other locality, it must have been long before traditional times, when the one tribe was broken up and nations formed. Races change so slow that they seem to be stationary. On the ancient Egyptian monuments are representations of the Negro, having exactly the same features which characterize that race at the present time; and some of these paintings date as far back as 2000 B. C. Then from the unity of the race and the persistency in type, an almost incredible length of time must be assigned to permit of the great disparity as exhibited by the different types of mankind. CHAPTER XVIII. THE BIBLE AND SCIENCE.