Page:Darwinism by Alfred Wallace 1889.djvu/163

From Wikisource
Jump to: navigation, search
This page has been validated.

eliminated by disuse. But this is entirely begging the question. Do meaningless peculiarities, which we admit often arise as spontaneous variations, ever perpetuate themselves in all the individuals constituting a variety or race, without selection either human or natural? Such characters present themselves as unstable variations, and as such they remain, unless preserved and accumulated by selection; and they can therefore never become "specific" characters unless they are strictly correlated with some useful and important peculiarities.

As bearing upon this question we may refer to what is termed Delbœuf's law, which has been thus briefly stated by Mr. Murphy in his work on Habit and Intelligence, p. 241.

"If, in any species, a number of individuals, bearing a ratio not infinitely small to the entire number of births, are in every generation born with a particular variation which is neither beneficial nor injurious, and if it is not counteracted by reversion, then the proportion of the new variety to the original form will increase till it approaches indefinitely near to equality."

It is not impossible that some definite varieties, such as the melanic form of the jaguar and the bridled variety of the guillemot are due to this cause; but from their very nature such varieties are unstable, and are continually reproduced in varying proportions from the parent forms. They can, therefore, never constitute species unless the variation in question becomes beneficial, when it will be fixed by natural selection. Darwin, it is true, says—"There can be little doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aid of any form of selection."[1] But no proof whatever is offered of this statement, and it is so entirely opposed to all we know of the facts of variation as given by Darwin himself, that the important word "all" is probably an oversight.

On the whole, then, I submit, not only has it not been proved that an "enormous number of specific peculiarities" are useless, and that, as a logical result, natural selection is "not a theory of the origin of species," but only of the origin

  1. Origin of Species, p. 72.