An Introduction to a Biology 



it, which would depend on a series of contingencies the 

 production of two such beasts at the same time, at the same 

 place, of opposite sexes, and the condition that they were not 

 averse to one another ; or it might unite with a trunkless 

 relative. But even in the former case the offspring would have 

 a smaller trunk than its two parents. And if this smaller trunk 

 were to be perpetuated its owner would have to unite with 

 another trunk-bearing variety, which therefore would have 

 to arise at the proper time, be of the opposite sex, and in 

 the neighbourhood ; but even if the smaller trunk were lucky 

 enough to find such a one its offspring would be less trunked 

 even than itself ! If the original trunked variety paired 

 with a trunkless relative the swamping would be ever so 

 much faster. But I leave the reader to pursue this argu- 

 mentation for himself suffice it to say that these trunk- 

 bearing sports would on this view be very soon wiped out. 



But if we adopt the conceptions of gametic purity and 

 unit-characters, there is no reason, when once the varia- 

 tion has arisen, why it should not be perpetuated. For 

 its germ-cells represent trunk-bearing elephants ; if it mated 

 with a similar beast its offspring would all be trunk-bearing 

 and in the same degree ; if, on the other hand, it met a 

 trunkless form, the result of such a union the hybrid, in 

 other words would have a trunk if the possession of that 

 organ were dominant, and would not if it were recessive ; 

 but whichever of these was the case, 25% of the next genera- 

 tion would be true-breeding trunk-bearers ; and so on. 

 This illustration may be crude, but I hope it shows the kind 

 of way in which, according to these new conceptions, such 

 a variation might be perpetuated ; while according to the 

 biometric view of heredity this would not be the case. 



We have seen that a single unit-character continues to 

 produce its like so long as it unites with its like until a new 

 variation arises from it ; but, when we come to consider 

 (c) Compound characters, we find that new characters can 

 arise in another way than by a discontinuous variation. 



