Duration of life 257 



All these facts prove that the velocity of development of animal 

 life in Arctic regions, where the temperature is near the freezing 

 point of water, must be from two to three times smaller than in 

 regions where the temperature of the ocean is about 10 C. and from 

 four to nine times smaller than in seas the temperature of which 

 is about 20 C. It is, therefore, exactly the reverse of what we 

 should expect when authors state that the density of organisms at or 

 near the surface of the ocean in polar regions is greater than in more 

 temperate regions. 



The writer believes that this paradox finds its explanation in 

 experiments which he has recently made on the influence of tempera- 

 ture on the duration of life of cold-blooded marine animals. The 

 experiments were made on the fertilised and unfertilised eggs of the 

 sea-urchin, and yielded the result that for the lowering of tempera- 

 ture by 1 C. the duration of life was about doubled. Lowering the 

 temperature by 10 degrees therefore prolongs the life of the organism 

 2 10 , i.e. over a thousand times, and a lowering by 20 degrees pro- 

 longs it about one million times. Since this prolongation of life 

 is far in excess of the retardation of development through a lowering 

 of temperature, it is obvious that, in spite of the retardation of 

 development in Arctic seas, animal life must be denser there than in 

 temperate or tropical seas. The excessive increase of the duration of 

 life at the poles will necessitate the simultaneous existence of more 

 successive generations of the same species in these regions than in 

 the temperate or tropical regions. 



The writer is inclined to believe that these results have some 

 bearing upon a problem which plays an important role in theories of 

 evolution, namely, the cause of natural death. It has been stated 

 that the processes of differentiation and development lead also to the 

 natural death of the individual. If we express this in chemical 

 terms it means that the chemical processes which underlie develop- 

 ment also determine natural death. Physical chemistry has taught 

 us to identify two chemical processes even if only certain of their 

 features are known. One of these means of identification is the 

 temperature coefficient. When two chemical processes are identical, 

 their velocity must be reduced by the same amount if the tempera- 

 ture is lowered to the same extent. The temperature coefficient for 

 the duration of life of cold-blooded organisms seems, however, to 

 differ enormously from the temperature coefficient for their rate of 

 development. For a difference in temperature of 10 C. the duration 

 of life is altered five hundred times as much as the rate of develop- 

 ment ; and, for a change of 20 C., it is altered more than a hundred 

 thousand times as much. From this we may conclude that, at least 

 for the sea-urchin eggs and embryo, the chemical processes which 



D. 17 



