222 LECTURE VIII. 



have arisen and have perished like the flowers in summer. 

 Species has further been defined as a collection of individuals 

 who transmit their characters regularly and indefinitely j but 

 it has not been considered that thousands of species have be- 

 come extinct^ some of them even in historical times, specimens 

 of which are only to be seen in our museums. To cite only 

 one instance of this kind, I would mention that the great auk 

 {Alca impennis) , which formerly inhabited Denmark, and in 

 1842 still existed in Iceland, is now entirely extinct, so that 

 only some twenty of their skins are preserved in different 

 museums. Species, then, is alterable by external influences, 

 and arises and perishes like individuals. 



On more closely examining the definitions of race and 

 species, sanctioned by usage, it may be reduced to an historical 

 basis. We assume races where we know, or think we know, 

 their common origin ; we assume species where their origin is 

 hidden in the past. We assume races in domestic animals 

 where, by our interference, we have succeeded in producing 

 varieties. We assume races in mankind, because we believe 

 we have evidence that the differences in form have arisen in 

 historical times. No man would certainly have doubted the 

 specific difierence in mankind, if the unity of the human 

 species had not to be defended at any price, — if a tradition had 

 not to be supported in opposition to the plainest facts, — a 

 tradition which has been the more venerated because it runs 

 counter to positive science. 



As regards species, then, we hold fast by the principle that 

 the genus Homo consists of several species, which deviate from 

 each other as much, if not more, than most simiaclce ; and if 

 the principles of systematic zoology are to be of any value, 

 they must be as applicable to the human as to the simious 

 species. 



With regard to general classification, we distinguish genera, 

 families, orders, classes, provinces, and kingdoms ; the latter 

 being the great divisions constituting the animal, the vege- 

 table, and the mineral kingdom, comprehending all existing 

 forms. We shall now examine the relations in which the 

 species of mankind stand to this classification. 



