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This distinction holds good for all cases in which the relationship between the forms in question is well known. It seems entirely justifiable therefore to apply it also to cases in which the systematic affinity is doubtful, as well as to instances in which it is impossible to arrive at any taxonomic conclusions.
But we are entirely warranted in concluding from these facts that in very many cases, perhaps in most, our system of taxonomic classification of animals and plants has gone altogether too far, and that scientists have erected specific distinctions which are wholly uncalled for and which confuse and obscure the main issues of the species problem.
But they have at least the merit that they give a vivid impression of what is most plausible and attractive in the idea of descent, and moreover they have helped towards orientation in the discussion. Nor can we ignore the very marked taxonomic and architectonic talent which their construction displays. Weismann’s Evolutionist Position.
Indeed there is every reason to believe that almost countless numbers of our taxonomic species have originated from common ancestral originals. But as these so-called species are now known to be freely or moderately cross fertile with other related species, their hybrids following the ordinary laws of Mendelian inheritance, we see that they are not true species but mere analytic varieties.
Systematists have always distinguished between adaptive characters and those of taxonomic value those which show the true affinities and they are perfectly right: also they have always distrusted and held aloof from theories of evolution which profess to explain all characters by one universal formula.
The extreme application of the principle would no doubt disturb the limits between many species and varieties as now recognized. It is not to be forgotten however that all taxonomic distinctions, which have not been confirmed by physiologic tests are only provisional, a view acknowledged by the best systematists.
No doubt, if attained, such an analysis would give us a deep insight into the real internal construction of the intricate properties of organisms in general. But taxonomic studies in this direction are only in their infancy and do not give us the material required for such an analysis.
Besides the direct comparison of the mutations described in our former lectures, with the analogous cases of the horticultural and natural production of species and varieties at large, another way is open to obtain the required proof. It is the study of the phenomena, designated by Casimir de Candolle by the name of taxonomic anomalies.
In short, we now know that our taxonomic classifications have been marked off on altogether too narrow lines. This has tended greatly to confuse the question at issue.
The shortening and spinulation of the scales are greatest in punctatus, least in norvegicus. In punctatus there are teeth on the vomer, in unimaculatus none, in norvegicus they are very small. If we consider fishes in general, we see that there is no evidence of any relation between many of the most important taxonomic characters and function or external conditions.
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