154 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



At about the turn of the present century, a reaction set in against 

 views on animal behaviour that had prevailed for a long time, in 

 which it was supposed, without much thought, that other animals are 

 actuated by emotions very similar to our own. Loeb (191 8) showed 

 that in some cases, the movements of animals could be interpreted as 

 mechanical reactions to applied stimuli. For example, an insect that 

 flies towards the light will fly along a line bisecting the angle between 

 two Ughts of equal intensity, and will fly in a circle if one eye is 

 blackened. Loeb's facts were right, but he stretched his interpretations 

 too far. If I were placed in a dark tunnel with a light at one end, I 

 should almost certainly walk towards the light, but my daily life 

 cannot be summed up by saying that I am positively phototactic. 

 Tinbergen (195 1) has described Loeb's tropism theory as a grotesque 

 simplification. When I was dealing with the behaviour of very young 

 tadpoles, however, I was able to describe their actions as a combination 

 of a kinesis, that is a random movement of restlessness in the absence 

 of enough oxygen, and a negative geotaxis, causing them to swim 

 upwards. This is pure Loeb, but then these are very simple animals, 

 only just capable of movement. When, much later in the Hves of the 

 tadpoles, I found a difliculty in explaining the avoidance by small 

 tadpoles of the company of their larger fellows, I suggested that some- 

 thing in tadpole psychology was involved. In this, I was agreeing with 

 Bierens de Haan (1948), who has strongly urged that even the simplest 

 animals have a psychology, and that, little as we may understand of it, 

 we should admit that a full synthesis of the elements of behaviour is 

 impossible without recognizing this as a fact. 



In considering the choice of ponds by frogs, I was convinced that the 

 clue lay in the special requirements of the different species, so that each 

 came to seek the environment most suitable to it, by physical means 

 no doubt, but according to a principle of directiveness or adaptiveness, 

 which is close to the ideas of E. S. Russell (1945). Russell has dehber- 

 ately rejected the mechanistic interpretations of behaviour, because he 

 tliinks that they leave out all that is distinctive of life. In most of the 

 following pages, I fmd that I can interpret what happens very much as 

 I think the behaviourists such as Tinbergen would do. They beheve 

 that the approach to the study of animal behaviour should be entirely 

 objective, and should proceed by a step-by-step analysis. Tinbergen 

 in his book has given a very fair appreciation of his own views in 

 relation to the others I have mentioned, and has made it clear that he 



