THE WONDERS OF LIFE 



actions, and it was believed that every species of animal 

 had special instincts implanted in it by the Creator. 

 Animals were thought, according to Descartes's view, to 

 be unconscious machines whose actions proceed with 

 unvarying constancy in the particular form that God 

 had ordained. Although this antiquated theory of in- 

 stinct is still taught by many dualistic metaphysicians 

 and theologians, it has long since been -demolished by 

 the monistic theory of evolution. Lamarck had observed 

 that most instincts are formed by habit and adapta- 

 tion, and then transmitted by heredity. Darwin and 

 Romanes especially showed afterwards that these in- 

 herited habits are subject to the same laws of variation 

 as other physiological functions. However, ' Weismann 

 has recently taken great pains in his Lectures on the 

 Theory of Descent (xxiii.) to refute this idea, and in gen- 

 eral the hypothesis of an inheritance of acquired char- 

 acters, because it will not harmonize with his theory of 

 the germ-plasm. Ernst Heinrich Ziegler, who has re- 

 cently (1904) published a subtle analysis of former and 

 present ideas of instinct, agrees with Weismann that 

 "all instincts are due to selection, and that they have 

 their roots not in the practice of the individual life, but 

 in the variations of the germ." But where else can we 

 find the cause of these " germ- variations " except in the 

 laws of direct and indirect adaptation ? In my opinion, 

 it is just the reverse; the remarkable phenomena of in- 

 stinct yield a mass of evidence of progressive heredity, 

 completely in the sense of Lamarck and Darwin. 



The great majority of organisms live social lives, and 

 so are united by the link of common interests. Of all 

 the relations which determine the existence of the 

 species, the chief are those which bind the individual to 

 other individuals of the species. This is at once clear 

 from the laws of sexual propagation. Moreover, the 

 association of individuals is a great advantage in the 



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