6o4 LIFE : OUTLINES OF GENERAL BIOLOGY 



very apt to occur \Nnth a smooth-backed tortoise; and the intelli- 

 gence might lie in taking advantage of a useful accident and one 

 that would be likely to happen over and over again and with 

 different eagles. Similar behaviour has been often observed on the 

 part of herring-gulls, which lift crabs, sea-urchins, and clams in their 

 bills and let them fall on the rocks or shingle below, with the result 

 that the hard shells are broken. In some places and on some occa- 

 sions this may be observed frequently among the gulls, and then 

 it may not be observed again for a long time. This requires further 

 observation ; but it suggests repeated re-discovery as the result of a 

 natural accident. Rooks deal in a similar way with freshwater 

 mussels. 



Caution Necessary in Experiment.— As a general rule it may 

 be said that animals are not cleverer than they need to be ; and mis- 

 taken inferences are sometimes drawn from cases where the animal 

 shows little or no hint of intelligence, simply because the situation 

 made no appeal to its interest or desire. This is well illustrated by 

 domesticated animals, which live a very sheltered life, with abundant 

 food and little in the way of danger or adventure. Hence we speak 

 contemptuously of "the brains of a hen", in contrast to those of a 

 crow in natural conditions, or even of a tame parrot, whose captivity 

 is full of interest. In cases like horses and dogs, which become 

 man's partners and share in his responsibilities, the domestication 

 keeps the brain active, and there has, of course, been persistent 

 selection in the direction of intelligence. We wish to linger for a 

 little over the behaviour of hens. 



Different breeds vary considerabh^ but expressions of intelligence 

 are not common, and in many cases the hen seems to be distinctly 

 stupid. It may fail, for instance, in the course of many weeks to 

 learn the simple device of putting one foot on a loose lettuce-leaf, 

 which is pecked at ineffectively because it is jerked away and often 

 lost at every peck. A common interpretation is that the hen's brains 

 have racially degenerated, either through disuse or because there 

 has been no selection in the direction of intelligence. But in all 

 probability this interpretation is wrong; first because it takes a long 

 time for brains to undergo racial degeneration — evolution up and 

 evolution down being slow racial processes; and, secondly, because 

 of the very marked mental alertness of the chicks. What happens 

 is an individual retrogression in the hen's lifetime, because the 

 artificial conditions afford insufficient stimulus. Sufficiently 

 awaken the need or the desire, as we shall see, and the hen's brain 

 rises to the occasion— a Natural History fact of considerable 

 importance. 



If an instinct be an inborn, ready-made power of doing apparently 

 clever things, then chicks have relatively few instincts — as com- 



