SPONTANEOUS VARIATIONS 39 



of heredity, spontaneous variations may for the present be 

 taken as meaning all those variations which arise independ- 

 ently of any direct l and immediate action of the environ- 

 ment. Presently we shall be in a position to give them a 

 narrower signification. 



We have, then, these two theories of heredity : the 

 doctrine that variations are due, as a general rule, to the 

 immediate and direct action of the environment on the germ- 

 plasm, and the doctrine that they are not so due, but arise, as 

 a rule, " spontaneously." The two doctrines, as commonly 

 formulated, are not entirely exclusive. Most biologists admit 

 the existence both of spontaneous variations and of variations 

 caused by the immediate and direct action of the environment. 

 But biologists differ greatly in the relative importance they 

 attach to the two factors. 



66. Now it is certain that some variations, at least, arise 

 spontaneously. The same phenomena which enabled us to 

 prove that all variations are not due to the transmission of 

 acquirements enable us to demonstrate, also, that they are 

 not all due to the influence of the environment. For 

 example, the germ-cells from which a litter of puppies, 

 kittens, or pigs arise are all exposed to practically the same 

 environmental influences, yet the germ-plasms contained in 

 them often differ immensely in hereditary tendencies, as is 

 proved by the great range of variations which may occur 

 among the different members of the same litter. It may be 

 maintained of course that germs vary because, being differently 

 situated in the reproductive organs, they are differently acted 

 on by the play of forces from the environment. But when we 

 remember how thoroughly the reproductive organs are pro- 

 tected, how completely they are permeated by blood and 

 lymph channels, and how small, therefore, the differences of 

 nutrition and environment must be, this hypothesis appears 

 very far-fetched. It is incredible, for example, that one child 

 should inherit exclusively paternal characters while another 

 inherits exclusively from the mother, or that one child should 

 have five digits on a limb while another has six or seven, or 

 that one puppy of a litter should be big and brown and rough- 



1 Direct as opposed to the indirect influence of Natural Selection. 

 Thus if the toxins of malaria were to injure the germ-plasm (and there- 

 fore, the offspring) of those individuals who suffered from that disease 

 their action would be spoken of as direct. But, if they merely altered 

 the germ-plasm of the race, by weeding out the unfit, their action would 

 be indirect. The word " immediate " is used in opposition to " remote." 

 Some biologists believe that the environment does not now influence the 

 germ-plasm, but that it did so in a very distant past. 



