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 {227} 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.