LINN-'^iAN DEFINITION OF SPECIES. 89 



Those who defend the stability of species rather imagine 

 that, with Cuvier, they are entitled to interpret facts in 

 their own favour ; whereas they partly remain uncon- 

 sciously involved in hereditary prejudice, and partly 

 contrive to be deliberately blind to all that evidently 

 contradicts the immutability of species. 



Since Linnseus referred to the Creation, he attributed 

 the individuals to a species, of w^hich the pedigree 

 ascended in direct line to the pair which proceeded 

 from the hand of the Creator. Owing to the state of 

 science in general, an examination of this pedigree was 

 totally impossible in his time ; and, indeed, with the 

 strict reliance on sacred tradition, it was scarcely neces- 

 sary. Cuvier, although a very unprejudiced and cool 

 observer, nevertheless radically accepted the Linnaean 

 definition of species. According to him, the species 

 is the aggregate of individuals descending from one 

 another and from common ancestors, and of those 

 who resemble them as strongly as they resemble one 

 another.^* 



"In this definition," 'says Haeckel, "to which the 

 majority have ever since more or less closely adhered, 

 two things are obviously required of an individual as 

 belonging to a species : in the first place, a certain 

 degree of resemblance or approximate similarity of 

 character ; and secondly, a kindred connection by the 

 bond of a common descent. In the numerous attempts 

 of later authors to complete the definition, the chief 

 stress is laid sometimes on the genealogical consangui- 

 nity of all the individuals, sometimes on morphological 

 uniformity in all essential characters. But it may be 

 generally asserted that in the practical application of 



