206 THE ORIGIN OF SPECIES [pt. ii 



mechanical. These phenomena, as has already been shown, can- 

 not be satisfactorily explained by any of the many suppositions 

 that have long been current, based upon natural selection. A 

 differentiating cause like natural selection could not produce 

 such uniformity of expression, and at the present time, the only 

 feasible explanation in the field seems to be that provided by 

 Age and Area, which explains the species and genera as developed 

 in successive order and gradually expanding their area (and 

 their number of species, in the case of genera) as time goes on. 



But if this explanation be correct, it is clear that the smaller 

 the area occupied by a species, the younger on the average will 

 it be, in its own circle of affinity. The only logical conclusion to 

 this is that in general the minimum area is that occupied by 

 species just commencing their life as such. But, as already shown 

 (pp. 54, 55), this may be very small indeed; a species may be 

 easily hmited to a dozen or two of individuals, if it does not 

 actually begin wirh one or the progeny of one^ It is clear that 

 we cannot regard as the formative cause of the genesis of the 

 species a struggle for existence resulting in the conservation of 

 favourable variations, especially if these be of the kind that we 

 understand as infinitesimal or fluctuating. 



The new species just commencing will have to undergo a 

 struggle for existence, usually of a very strenuous kind, imme- 

 diately, and if in any way unsuitable to the conditions that pre- 

 vail at the exact place and time of its birth, will at once die out, 

 as a rule leaving no trace. If it survive, it may contiiaie to 

 spread so long as it finds conditions in which it can grow, and 

 the ultimate area that it covers will depend upon that and upon 

 its age (cf. de Vries, below, p. 227). 



One of Darwin's innumerable services to the cause of science 

 was to call attention to the struggle for existence. Even he, 

 however, perhaps hardly emphasised sufficiently the intensity 

 of that which j^robably takes place at the birth of a species, 

 except upon more or less virgin soil. If in any xvay unsuited to 

 the conditions obtaining at the time and place, it will be all but 

 certain to succumb. IMere heredity, however, will tend to make 

 it more or less suitable. But even if well suited, the new species 



1 A few days before I left Rio, Dr Lofgren found, on a little island about 

 three miles off the coast, a new and very distinct Rhipsalis, of enormous 

 size. He told me that there were only four examples on the island. I could 

 only find, on the summit of Ritigala, about a dozen examples of Coleus 

 elongatus (p. 54). And cf. Didymocarpus and Christisonia, p. 151. 



