BIOLOGICAL PHILOSOPHY 435 



or two other kinds of fish. The production of electricity by hfe might 

 justly have appeared as something rare and sporadic. However, as physi- 

 ology progressed, it was found that electric currents pass when a nerve 

 is stimulated, when a muscle contracts, when a gland secretes; in fact we 

 know that all vital activities, of whatever kind, from conscious thought 

 to the fertilization of the egg, are accompanied by some electrical activ- 

 ity. 



In the electric eel, certain muscles have been modified so that though they 

 have lost their original function of contraction, their electric discharges 

 are accumulated as in a galvanic pile, and the total voltage and current are 

 quite respectable. Whereas in the great majority of cases the electrical 

 properties of living matter play no special part in the life of the animal, they 

 have become the specific function of the eel's electric organs: an accident 

 of nature has become biologically significant. 



One may suggest that the same sort of thing has happened with mind. All 

 the activities of the world stuff are accompanied by mental as well as by 

 material happenings; in most cases, however, the mental happenings are 

 at such a low level of intensity that we cannot detect them; we may per- 

 haps call them "psychoid" happenings, to emphasize their difference in in- 

 tensity and quality from our own psychical or mental activities. In those 

 organs that we call brains, however, the psychoid activities are, in some 

 way, made to reinforce each other until, as is clearly the case in higher 

 animals, they reach a high level of intensity; and they are the dominant and 

 specific function of the brain of man. 



In evolution, science has not merely revealed the bridge that provides 

 continuity between man and lifeless matter, but has also discovered what 

 is perhaps the most important single biological fact yet known — the fact of 

 evolutionary progress. A great deal of evolution is mere diversification. 

 New species constantly arise, adapted to slightly different conditions, or 

 produced by the biological accidents of isolation or hybridization. Through 

 this frill of diversity, however, there can be perceived a series of long- 

 range trends, whose course runs for millions or tens of millions of years. 

 The great majority of these trends are specializations. They fit the existing 

 type more closely to one mode of life, and in so doing cut it off from suc- 

 cess in others. In the evolution of higher mammals, for instance, one line 

 specialized as predators, and became the carnivores; another specialized in 

 chewing and digesting foliage and herbage, and usually in swift running, 

 to become the ungulates; a third in flying — the bats; a fourth in marine life 

 — the whales and porpoises; and so on. It is a universal rule that one-sided 

 specializations eventually come to a dead end. There is a point beyond 

 which natural selection cannot push them. When a specialization has 

 reached its biomechanical limit, it remains unchanged — unless new com- 

 petition causes it to become extinct. Thus most mammals have not evolved 

 in any important way for ten or twenty million years, birds not for twenty 

 or twenty-five million, ants not for thirty million. 



