Heredity of Instincts. 27 



an hypothesis ; but as it is founded on heredity, and assigns to 

 it a very prominent part, it is impossible not to state it 



The reader is aware that a theory sketched by De Maillet, 

 Robinet, and especially Lamarck, accepted and modified by 

 Darwin and Wallace in our own days, has gained the assent of 

 many eminent men in England, Germany, and France. -Accord- 

 ing to this theory, species are variable, and are formed by the 

 accumulation of slight differences, which have been fixed by here- 

 dity. The genera and species now extant, however numerous 

 they may be, are derived from three or four primitive types, per- 

 haps from one only. It was only necessary that some variations 

 should occur spontaneously. If these variations were adapted to 

 new conditions of existence ; if they gave to the individual one 

 more weapon to fight the battle of life, and if they have been 

 transmitted by heredity, then a new species has been formed, 

 which, under the continued action of the same causes, has 

 departed more and more from the primordial type. Spontaneous 

 variations, the struggle for life, selection, time, and heredity these 

 are the factors by the aid of which can be explained the evolution 

 of living creatures, the formation and disappearance of species. 



This bold hypothesis has thrown an entirely new light on 

 instinct Since in all animals the physical and the mental con- 

 stitution are, as we have seen, correlated, if there were originally 

 none but rudimentary organisms, instincts must then have been 

 very rude. And again, since instinct, like the organism, presents 

 spontaneous variations, and like it is subject to the laws of the 

 struggle for life and heredity, we must conclude that if these 

 causes explain the formation of species, they will also explain the 

 formation of instincts. If a physical modification, by adapting an 

 animal to new conditions, produces a deviation that may become 

 fixed, because it constitutes a progress from antecedent states, the 

 same will be true of mental modifications. Every variation of 

 instinct that puts the animal in a better position to defend itself 

 against new enemies, or to capture some new prey, will make it 

 likely to survive under more complicated conditions. 



So long as species were regarded as fixed, the question of the 

 origin of instincts could not be even raised. The matter appeared 

 very simple : the species was sent into the world ready-made, with 



