A CONDITION OF EVOLUTION 3 



the material on which the many diverse forms of selection and 

 isolation operate. 



In olden days thoughtful men seemed to see the threads of 

 life within the hands of three sister Fates, — of one who held the 

 distaff, of another who offered flowers, and of a third who bore 

 the abhorred shears of death. So, in Scandinavia, the young 

 child was visited by three sister Norns, who brought characteristic 

 gifts of the past, the present, and the future, which ruled the 

 life to be as surely as did the hands of the three Fates. So, too, 

 in days of scientific enlightenment, we still think of Fates and 

 Norns, though our conceptions and terms are very different. 

 What the living creature is or has to start with in virtue of its 

 hereditary relation ; what it does in the course of its activity ; 

 what surrounding influences play upon it, — these are the three 

 determining factors of life. Heredity, function, and environ- 

 ment — famille, travail, lieu — are the three sides of the bio- 

 logical prism, by which, scientifically, we seek to analyse the light 

 of life, never forgetting that there may be other components 

 which we cannot deal with scientifically, just as there are rays of 

 light which our eyes can never see. 



In novels like Zola's Dr. Pascal, in plays like Ibsen's Ghosts, 

 in sermons and newspaper articles, in large books and health 

 lectures, in season and out of season, we have all heard in the 

 last few years much about the importance of heredity ; and 

 though it is to be feared that many widespread impressions on 

 the subject are misleading, the awakening of keen interest is 

 in itself a symptom of progress. What is now required is a 

 serious study of what has been securely established. Otherwise 

 we shall continue to think in platitudes and act on guesses. 



Practical Importance to Breeders and Cultivators. — And 

 what is important in regard to Man's heredity is even more 

 demonstrably important in regard to his domesticated animals 

 and cultivated plants. What has been achieved in the past in 

 regard to horses and cattle, pigeons and poultry, cereals and 



