CREATION BY EVOLUTION
Darwinian naturalists believed. A species is an expression of opinion, not of fact.
Persistent efforts were made to delimit species by the sterility of hybrids. The fact that the mule is sterile was set up as proof that the horse and the donkey are different species. But the rule that hybrids are sterile is subject to many exceptions; thus the rabbit and the hare have a fertile hybrid known as Lepus darwinii, and so have the common and the Chinese goose, which are classified as unquestionably distinct species. Conversely, crosses between many domesticated varieties of plants are sterile.
The fact that a species is an arbitrary and not a well-defined natural unit is further shown by variations of organisms from the standard types. Herbert Spencer, in 1852,[1] years before the publication of Darwin's Origin of Species, claimed that it had already been proved that “any existing species—animal or vegetable—when placed under conditions different from its previous ones, immediately begins to undergo certain changes of structure fitting it for the new conditions. They [the supporters of the theory of natural development] can show that in cultivated plants, in domesticated animals, and in the several races of men, such alterations have taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species are in other cases founded. They can show that it is a matter of dispute whether some of these modified forms are varieties or separate species.”
Some variations are obviously due to the influence of environment and of mode of living—of daily work. Variations that are successive and cumulative in time have been called mutations (Waagen, 1868), though that term has been
- ↑ Reprinted in Essays, Vol. 1, pp. 379-80, 1868.
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