The Making of Species 



lateral triangle, six of them going to each side. 

 Suppose now, that from some cause or other they 

 rearrange themselves to form an isosceles triangle, 

 so that only four form the base and seven go to 

 each of the remaining sides. Such an arrange- 

 ment would give rise to a mutation. Suppose now 

 that, from some cause or other, this triangular bio- 

 logical molecule were to split up into two triangles, 

 each having three atoms to each side, we should 

 obtain a still more marked mutation. We are 

 far from saying that the atoms in the organic 

 molecule ever take such forms. We have merely 

 attempted to give rough but simple illustrations 

 of the kind of processes which on this hypothesis 

 might be expected to take place in the germ cells 

 or the fertilised eggs. 



Let us now consider the sexual act from this 

 aspect. The various molecules (we speak, of 

 course, of biological molecules) of the male 

 parent meet those of the female parent, and a 

 synthesis occurs, which results in the formation 

 of a new organism. When these two sets of 

 gametes meet one another, one of several events 

 may happen. The gametes may refuse to com- 

 bine. This will occur whenever they are of 

 very different constitution ; thus it is that widely 

 differing species will not interbreed. But it may 

 even happen that gametes of individuals of the 

 same species may refuse to coalesce on account 

 of some peculiarity in the composition of one or 



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