266 PRESIDENTIAL ADDRESS. 



tion of the eyes, with accompanying asymmetry of the skull 

 and adjoining parts, is a variation of not very frequent 

 occurrence. Still less frequent must be the asymmetry in 

 the particular direction required. The chances against 

 individuals possessing these very infrequent favourable 

 variations happening to mate together would be many to 

 one. And I take it to be exceedingly questionable whether 

 the non-possession of an incipient asymmetry would con- 

 stitute a character of elimination value. In which case 

 there would be no selection of the incipient asymmetrical 

 variety. 



It is possible, however, that asymmetry in a marked degree 

 occurred as a sport like the Ancon ram ; that this sport was 

 subject to exclusive inheritance ; and that in this way there 

 arose a variety which, being in harmony with the conditions 

 of life, throve and multiplied, and eventually ousted the 

 parental stock. If species have frequently arisen in this 

 way, we must give up the old adage Natiira nil facit 

 per saltum. And in this connection we must remember 

 that Darwin regarded the occurrence of a sudden strong 

 deviation from symmetry as highly improbable. He says : 

 " Mr. Mivart remarks that a sudden spontaneous transfor- 

 mation in the position of the eyes is hardly conceivable, in 

 which I quite agree with him." Mr. Darwin's own account 

 is entirely based on the view that the acquired effects of 

 " straining the lower eyes so as to look upwards " are in- 

 herited. 



In considering the swamping effects of intercrossing, Dar- 

 win candidly states that, until he read the now celebrated 

 article by Professor Fleeming Jenkin in the North British 

 Review, he " did not appreciate how rarely single varia- 

 tions, whether slight or strongly marked, could be perpetu- 

 ated." And he says further on : " It should not, however. 



