The Influence of Physical Conditions in the Genesis of Species [Influence des conditions physiques dans la génèse des espèces].

Résumé

Among biologists who accept the modern theory of evolution as the only reasonable hypothesis available for the explanation of the diversity of structure among organized beings, there is a wide difference of opinion as to what are the leading causes of differentiation. The doctrine of natural selection, or the survival of the fittest, has recently been brought prominently forward as the key to this complex problem, and is upheld by a large class of enthusiastic adherents, who accept it as the full solution of the whole question. By others the conditions of environment are believed to be far more influential in effecting a certain class of modifications, at least, that the necessarily precarious influence of natural selection, which must take its origin in isolated instances of variation in favourable directions, and depend for its continuance upon these fortuitous advantages being inherited by the descendants of the favoured individuals in which they originate. The modifying influence of conditions resulting from geographic or climatic causes, was long since noticed, and for nearly a century has been considered by many writers as explanatory of much of the diversity existing not only in the human race, but among animals. It has, however, remained, until recently, vaguely grounded, being based more in conjecture than on observed facts. Scarcely, indeed, have two decades passed since the real nature and extent of geographical variation among animals, and even as yet among only a few species, began to receive careful attention, while only within the last fifteen years has any attempt been made to correlate the observed differences with the climatic or geographical conditions of habitat. Radical Review, 1877, 1:108.