Even in making an abstract of the difficulties always to be found in determining every animal _species_, difficulties which are derived from the way in which we understand its evolution,[328] must we be astonished that the human race is not yet divided into distinct groups, when animals, much more easy to class on account of their lesser degree of intellectual and social activity, are not yet classed in a satisfactory manner,[329] when the Geoffroys, Cuvier, and De Blainville have failed in something or other, since this question seems still worthy of examination by the greatest minds of Europe with which the natural sciences are honoured at the present day? The natural history of man is of to-day, and the difficulties are great, because by virtue of his intellect man possesses resistance and special affinity. Living by nations, he lives a double life; his own, and that of the nation--which is a separate thing--into which a neighbouring race or species can enter wholly, adopting the same customs, the same dress, and the same language. There are difficulties which we meet with in anthropology, and which we only meet with there. A species has been known to disappear, for instance, and has left its name to some group entirely different from it, for if the Ethnic name has served at the origin to name the inhabited country, the geographical name has reacted in its turn, and has imposed itself on all the people who have successively occupied the same area. Other difficulties will arise from regions inhabited by distinct species, if these limits are not marked by some physical barrier almost impossible to be passed. Thus we are far, even at the present day, from agreeing about the bases of a good anthropological classification. Many methods have been tried, but none have as yet succeeded. Some have adopted geographical division. Others, the colour of the skin. Others, the state of the hair. Others (the most numerous class), have stopped at the shape of the head. The skull has chiefly exercised the sagacity of anatomists and anthropologists, and we can say fairly that there is no combination to which it has not been submitted in order to arrive at the distribution of mankind into natural groups. We must remark that all these cranioscopic classifications rest involuntarily upon this _datum_, that the different kinds of men are unequally endowed with intellect. Starting, then, from this principle, that the volume of the brain is in _ratio_ to intelligence, or that intellect is in _ratio_ to the volume of the brain, people tried to find a simple, rather than an easy, method of taking account of such an irregular solid: and Camper opened the way with his famous angle.