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 vrould 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 w^as 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. 



^7^7 



