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.. but that in each successive generation the character in question has been lying latent, and at last, under unknown favourable conditions, is developed. With the barb-pigeon, for instance, which very rarely produces a blue bird, it is probable that there is a latent tendency in each generation to produce blue plumage. ↑ The abstract improbability of such a tendency being transmitted through a vast number of generations, is not greater than that of quite useless or rudimentary organs being similarly transmitted. A mere tendency to produce a rudiment is indeed sometimes thus inherited.
As all the species of the same genus are supposed to be descended from a common parent, it might be expected that they would occasionally vary in an analogous manner; so that a variety of one species would resemble each other, or that a variety of one species would resemble in certain characters another and distinct species,— this other species being, according to our view, only a well-marked and permanent variety. But characters exclu- sively due to analogous variation would probably be of an unimportant nature, for the preservation of all functionally important characters will have been determined through natural selection, in accordance with the different habits of the species. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... It might further be expected that the species of the same genus would occasionally exhibit reversions to long lost characters. As, however, we do not know the ... common ancestor of any natural group, we cannot distinguish between reversionary and analogous characters. If, for instance, we did not know that
distant, but that in each successive generation there has been a tendency to reproduce the character in question, which at last, under unknown favourable conditions, gains an ascendency. For instance, it is probable that in each generation of the barb-pigeon, which produces most rarely a blue and black-barred bird, there has been a tendency in each generation in the plumage to assume this colour. ↑ This view is hypothetical, but could be supported by some facts; and I can see no more abstract improbability in a tendency to produce any character being inherited for an endless number of generations, than in quite useless or rudimentary organs being, as we all know them to be, thus inherited. Indeed, we may sometimes observe that a mere tendency to produce a rudiment is inherited.
As all the species of the same genus are supposed, on my theory, to have descended from a common progenitor, it might be expected that they would occasionally vary in an analogous manner; so that the varieties of two or more species would resemble each other, or that a variety of one species would resemble in some of its characters another and distinct species, — this other species being on my view only a well-marked and permanent variety. But characters thus gained would probably be of an unimportant nature, for the presence of all important characters will be governed by natural selection, in accordance with the diverse habits of the species, and will not be left to the mutual action of the conditions of life and of a similar inherited constitution. It might further be expected that the species of the same genus would occasionally exhibit reversions to lost ancestral characters. As, however, we never know the exact character of the common ancestor of a group, we could not distinguish these two cases: if, for instance, we did not know that