text:  "Now unless all these observations are erroneous or capable of some explanation that has not yet been pointed out they lead with the strongest force of analogical reasoning to the conclusion that a number of different tribes such as the various races of men must either be incapable of intermixing their stock and thus always fated to remain separate from each other; or if the contrary should be the fact that all the races to whom the remark applies are proved by it to belong to the same species