THE CATEGORIES OF VARIANT INDIVIDUALS 61 



types of variation are 2 19 . Henry (1928, p. 65) has shown 

 that the chance that two human individuals will have the 

 same finger-print pattern for a given digit of one hand is of 

 the order of over 1,000,000 : 1 [cf. p. 24, supra). 



I. Taxonomig Categories 



The Linnean hierarchy of morphological groups of which 

 the species and variety are members is still the system by 

 which we express an animal's relationships. We do not wish 

 to discuss the general principles according to which this system 

 is constructed and its capacity to express animal relationships. 

 We may suspect with Bather (1927, p. ci) ' that the whole of our 

 system is riddled through and through with polyphyly and 

 convergence,' and we may agree that the chief and most philo- 

 sophic duty of the systematist is to ' free it from this reproach ' 

 (Bather, I.e.), even if this task presents difficulties which 

 may be occasionally insuperable (Robson, 1932). 



Nevertheless the species and the variety or subspecies are 

 the most frequently used categories, and they are the reference 

 points round which all the data as to habits, distribution and 

 variation have been assembled. It will be as well, therefore, 

 to commence our survey with them. The status of the species 

 has, of course, been subjected to long and painful inquiry. 

 It has been challenged on two principal counts — (a) that it is 

 an arbitrary abstraction from a number of individuals which 

 vary so much inter se that any grouping must do violence to 

 the natural divergences that are found both in time and place ; 

 and (b) that it is not a group having regularly definable proper- 

 ties and a standardised status vis-a-vis other groups. The 

 first of these objections questions the capacity of the systematist 

 to designate any part of a more or less continuous natural 

 assemblage, the second criticises the status of the species in 

 a hierarchy of classification. 



Most biologists are now agreed that the latter objection 

 is valid and that the species has no standardised attributes by 

 which it can be distinguished from the variety and the genus. 

 Such a standardisation, it is true, might be defined by the 

 acquisition of some qualities constituting critical upward and 

 downward limits in the process of evolutionary divergence 



