On the Genesis of Species

by St. George Jackson Mivart

The one modus operandi yet suggested having been found insufficient, the question arises, Can another be substituted in its place? If not, can anything that is positive, and if anything, what, be said as to the question of specific origination?

Now, in the first place, it is of course axiomatic that the laws which conditioned the evolution of extinct and of existing species are of as much efficacy at this moment as at any preceding period, that they tend to the manifestation of new forms as much now as ever before. It by no means necessarily follows, however, that this tendency is actually being carried into effect, and that new species of the higher animals and plants are actually now produced. They may be so or they may not, according as existing circumstances favour, or conflict with, the action of those laws. It is possible that lowly organized creatures may be continually evolved at the present day, the requisite conditions being more or less easily supplied. There is, however, no similar evidence at present as to higher forms; while, as we have seen in Chapter VII., there are a priori considerations which militate against their being similarly evolved.

The presence of wild varieties and the difficulty which often exists in the determination of species are sometimes adduced as arguments that high forms are now in process of evolution. These facts, however, do not necessarily prove more than that some species possess a greater variability than others, and (what is indeed unquestionable) that species have often been unduly multiplied by geologists and botanists. It may be, for example, that Wagner was right, and that all the American monkeys of the genus cebus may be reduced to a single species or to two.

With regard to the lower organisms, and supposing views recently advanced to become fully established, there is no reason to think that the forms said to be evolved were new species, but rather reappearances of definite kinds which had appeared before and will appear again under the same conditions. In the same way, with higher forms similar conditions must educe similar results, but here practically similar conditions can rarely obtain because of the large part which "descent" and "inheritance" always play in such highly organized forms.

Still it is conceivable that different combinations at different times may have occasionally the same outcome just as the multiplications of different numbers may have severally the same result.

There are reasons, however, for thinking it possible that the human race is a witness of an exceptionally unchanging and stable condition of things, if the calculations of Mr. Croll are valid as to how far variations in the eccentricity in the earth's orbit together with the precession of the equinoxes have produced changes in climate. Mr. Wallace has pointed out[^[229]] that the last 60,000 years having been exceptionally unchanging as

regards these conditions, specific evolution may have been exceptionally rare. It becomes then possible to suppose that for a similar period stimuli to change in the manifestation of animal forms may have been exceptionally few and feeble,—that is, if the conditions of the earth's orbit have been as exceptional as stated. However, even if new species are actually now being evolved as actively as ever, or if they have been so quite recently, no conflict thence necessarily arises with the view here advocated. For it by no means follows that if some examples of new species have recently been suddenly produced from individuals of antecedent species, we ought to be able to put our fingers on such cases; as Mr. Murphy well observes[^[230]] in a passage before quoted, "If a species were to come suddenly into being in the wild state, as the Ancon sheep did under domestication, how could we ascertain the fact? If the first of a newly-born species were found, the fact of its discovery would tell nothing about its origin. Naturalists would register it as a very rare species, having been only once met with, but they would have no means of knowing whether it were the first or the last of its race."

But are there any grounds for thinking that in the genesis of species an internal force or tendency interferes, co-operates with and controls the action of external conditions?

It is here contended that there are such grounds, and that though inheritance, reversion, atavism, Natural Selection, &c., play a part not unimportant, yet that such an internal power is a great, perhaps the main, determining agent.