280 P't^of. Guthrie^ LL.B, — On the Subjective Causes of [April 25, , 



specifically identical individuals of opposite sexes and specifically 

 differentiated from their ancestors, thus bringing us back practically to 

 the abandoned doctrine of specific creations. 



The individual or dual origin of species fails also in satisfactorily 

 explaining the extinction of a varying species. 



It seems to be generally held that existing species are collaterally, . 

 not lineally, related. Why this opinion is so generally entertained 

 is not very obvious. One reason perhaps is that species are not known 

 to sport into other species, which owing to atavism would sometimes 

 be the case if existing species were related in the direct ancestral 

 line. Now in the absence of a general tendency to variation on one 

 or some few directions, this extinction of the ancestral form is not 

 easily accounted for. If a species diffused over a floral area gives 

 rise to a variety in one particular spot, in the absence of any tendency 

 towards the same variation elsewhere, it seems almost impossible 

 that the new form should supersede the old. As Darwin has pointed 

 out, in order that a species may successfully invade a new region 

 it must not have any closely allied race to contend with. 



Successful invaders of an occupied area to a great extent belong 

 to genera not represented in the area they invade, and seldom or 

 never do they belong to species closely allied to species existing 

 there. Still less is it likely that a variety formed in one area will 

 pursue and exterminate the parent species in an area now detached 

 from that in which it originated. 



Whatever theory is entertained as to the origin of new varieties 

 must be also capable of explaining the disappearance of the form 

 from which it originated and in this respect the purely objective 

 theory of the production of new forms seems to fail. 



According to the theory of variation in a comparatively few 

 directions due to an innate law or tendency, cross-fertilization is a 

 distinct aid to the production of new species and to the extinguish- 

 ment of the old. 



Thus suppose a species A has a natural tendency to vary in a 

 direction which would ultimately produce a new species Z, and let the 

 first step of variation produce the form B. Let A be an annual and 

 let 20 per cent of its progeny take the B form. 



Some few of these B's may be cross-fertilized with each other, and 

 their inheriting the tendency to vary from both parents will leave 

 progeny of which the majority will pass into the C form, another step 

 towards the specific form Z. The great majority of the B's, however,. 



