EVOLUTION 933 



sometimes very varied and plastic, controlled by intelligence at 

 every turn, as is true of many of the ways of otters, foxes, and 

 monkeys. Or they may be predominantly instinctive, as in the ways 

 of ants, bees, and wasps. Or it may be that an animal's behaviour 

 includes a good deal that is more or less intelligently learned, along 

 with a good deal that is instinctive. Whenever a customary activity 

 has become so thoroughly engrained in the animal's constitution 

 that its performance requires no apprenticeship or learning, then 

 the animal may be more free to make experiments ; and many birds 

 and mammals show a happy mixture of instinctive behaviour (in 

 the wide sense of inborn or enregistered) and of intelligent behaviour 

 in the sense of profiting by experience and showing something in 

 the way of judgment. This is an intricate subject which we cannot 

 pursue further here {see Animal Behaviour section), but the impor- 

 tant point is that wild traits in tame animals are always of the 

 enregistered or instinctive type, never of the intelligent type. This 

 is why they sometimes last on in domestication after their original 

 utility is past ; they are part and parcel of the hereditary constitution. 

 It is not that new habits acquired under the conditions of domestica- 

 tion oust old habits which were established in the wild life of 

 ancestors, for this is using the word "habit" in two different senses. 

 The grip of the past on the behaviour of domesticated animals is 

 illustrated in reference to little ways which were enregistered in the 

 nervous system and formed part of the racial inheritance. The little 

 ways, like the dog's turning round and round before it falls asleep, 

 cannot suddenly disappear any more than the power of speech 

 would disappear in colonists who found themselves in a country of 

 the deaf and dumb. 



AN ILLUSTRATION OF THE EVOLUTIONARY SURVEY 

 OF THE ANIMAL KINGDOM 



A taxonomic classification aims at grouping organisms according 

 to their affinities or "blood-relationships"; and it is based, as we 

 have seen, on homologies or deep resemblances in structure and 

 development. But behind this systematic arrangement ^ no easy task 

 in itself, there is the more difficult problem of interpretation. Can 

 the evolutionary alternatives and trends be detected — even with 

 plausibility — which have resulted in the at first sight bewildering 

 manifoldness among the forms of animal life? If we think of the 

 various phyla, classes, orders, families, genera, and species as 

 arranged on a complex genealogical tree, can we discern in any 

 degree the mode of branching? Such is the ambitious task which 

 we wish now to illustrate. 

 The Fundamental Dichotomy. — In every organism, as we have 



