928 LIFE: OUTLINES OF GENERAL BIOLOGY 



not due to the absence of pigment -forming factors, since a Proteus 

 well illumined may become dark in a week. What is lacking is the 

 liberating stimulus of light. The same holds, even more dramatically, 

 for the eyes. The Proteus is blind, partly perhaps because its eye 

 primordium is ah initio lacking in developmental vigour, but partly 

 because the absence of the appropriate liberating stimulus causes 

 in each individual an arrest of development. 



PERSISTENCE OF ANCESTRAL HABITS 



Darwin was very characteristically interested in the dog's not 

 infrequent habit of turning round and round on the hearthrug, as 

 if to smooth down the herbage and make a comfortable bed for the 

 night. It has been occasionally seen when a country-dog goes to 

 sleep among the grass, and it is a habit among wolves, from which 

 domesticated dogs are derived ; and the habit has lasted for many 

 thousands of years since Neolithic Man first succeeded in making the 

 dog his partner. No doubt the habit of turning round and round 

 would be useful in ancient days before there were houses in the 

 modern sense, but it has long ceased to be necessary, and yet it 

 persists. It illustrates the hand of the past on the present. Perhaps 

 there is also some significance in the fact that the past asserts 

 itself in this case in the sleepy dog, when the unconscious has more 

 chance to exert its influence than in wideawake hours. 



The same survival of habits is seen when the well-fed dog buries 

 a bone or some remains of its meal, for this is a wild trait seen, for 

 instance, in the fox. Another thing we have all seen a dog do, is 

 scratching backwards with its hind feet, as if to throw earth over 

 its excrement. It no longer succeeds in doing this; and there is 

 obviously no sense in scratching, as it often does, on a bare pave- 

 ment. The past lives on, and a habit may outlive its usefulness. 



Darwin gave a number of instances of habit-survival in his book 

 on The Variation of Animals and Plants under Domestication 

 (1868) ; and there is an interesting book by Robinson on Wild Traits 

 in Tame Animals. Let us bring together some examples. 



Some cattle were transported from Aberdeenshire to a Californian 

 ranch, where they found themselves in relatively wild conditions. 

 It was observed that when a cow calved away from the farm, which 

 is not favoured in Britain, she hid her calf in a thicket when she 

 went out to graze. This hiding of the calf is a wild habit, which had 

 remained dormant for many generations of men and cattle, but had 

 reasserted itself when there was a change towards more natural 

 surroundings. Here it may be recalled that cattle disturbed 

 when at rest rise on their hind legs first, while horses rise on their 

 front legs first; part of the explanation being that the wild horses 



