450 The American Naturalist. [June, 



5. It seems to me also — though I hardly dare venture into a 

 field belonging so strictly to the technical biologist — that 

 this principle might not only explain many cases of widespread 

 "determinate variations" appearing suddenly, let us say, in fossil 

 deposits, but the fact thai variations seem often to be " discon- 

 tinuous." Suppose, for example, certain animals, varying, 

 in respect to a certain quality, from a to n about a mean 

 x. The mean x would be the case most likely to be preserved 

 in fossil form (seeing that there are vastly more of them). 

 Now suppose a sweeping change in the environment, in such 

 a way that only the variations lying near the extreme n 

 can accommodate to it and live to reproduce. The next 

 generation would then show variations about the mean n. 

 And the chances of fossils from this generation, and the subse- 



ild be < 



approximating 



would be a great discontinuity in the chain and also a wide- 

 spread prevalence of these variations in a set direction. This 

 seems especially evident when we consider that the paleontol- 

 ogist does not deal with successive generations, but with 

 widely remote periods, and the smallest lapse of time which he 

 can take cognizance of is long enough to give the new mean 

 of variation, n, a lot of generations in which to multiply and 

 deposit its representative fossils. Of course, this would be 

 only the action of natural selection upon " preformed " varia- 

 tions in those cases which did not involve positive changes, in 

 structure and function, acquired in ontogenesis ; but in so far as 

 such ontogenetic adaptations were actually there, the extent 

 of difference of the n mean from the x mean would be greater, 

 and hence the resources of explanation, both of the sudden 

 prevalence of the new type and of its discontinuity from the 

 earlier, would be much increased. This additional resource, 

 then, is due to the " Organic Selection " factor. 



We seem to be able also to utilize all the evidence usually 

 cited for the functional origin of specific characters and group- 

 ings of characters. So far as the Lamarkians have a strong 

 case here, it remains as strong if Organic Selection be substi- 

 tuted for the " inheritance of acquired characters." This is 

 especially true where intelligent and imitative adaptations are 



