PHYSICAL INVESTIGATION. 



In itself, it is of little importance what signification is given to 

 the term " species"; but so much depends upon it, that unity of 

 descent, which requires a separate proof, should not be in- 

 cluded in the notion of typical equality of beings. The con- 

 ception of species does not merely belong to zoology and botany, 

 but to all sciences ; the former must, therefore, if necessary, 

 give it a more precise definition ; but, at the same time, should 

 keep it free from theoretical assumptions, as it is merely in- 

 tended to designate the actual facts. If in modern times there 

 prevail an inclination to designate every variety as an original 

 species, ' ' which despite of all external influences remains per- 

 manent," and to consider this character of permanency of type, 

 even under unfavourable circumstances, as the sole criterion of 

 species, 1 a definition is then given, which, in itself, is not 

 objectionable ; but there is then danger to overlook or alto- 

 gether deny the actually existing variability of type, so that the 

 conception of species (as is the case in Morton and his disci- 

 ples, of the American school), is in fact a mere definition pre- 

 pared in order to arrive at the intended result of a plurality of 

 the human species. 



Like separate descent, so also has fecundity been considered 

 as a criterion of difference of species, founded chiefly upon the 

 following facts : 



In a state of perfect liberty, and under normal conditions, 

 animals of the same type not only pair with each other, but 

 usually select, by preference, such individuals of the same type 

 as resemble them most, especially as regards colour. Cross- 

 ing of different types and the production of hybrids, occur in 

 the free state only under abnormal circumstances, and if inten- 

 tionally occasioned by man, they succeed only by the agency 

 of artificial means. The mare must be blindfolded if she is to 

 be covered by the male ass ; the ass must be painted over like 

 a zebra to couple it with that animal, and even such means 

 succeed only when the individuals belong to nearly allied 

 species. The produced hybrids are in most cases sterile, or if 



1 So Agassiz, in Nott and Gliddon, who defines species as the sum of indi- 

 viduals which, since it has been known to man, has always retained the same 

 peculiarities. Desnioulins, " Hist. Nat. des Races Huniaines," p. 194, 1826. 



