Origin of Species Variorum

In members of the same class the average amount of change, during long and equal periods of time, may, perhaps, be nearly the same; but as the accumulation of long-enduring formations, rich in fossils, depends on great masses of sediment being deposited on subsiding areas, our formations have been almost necessarily accumulated at wide and irregularly intermittent intervals of time; consequently the amount of organic change exhibited by the fossils embedded in consecutive formations is not equal. Each formation, on this view, does not mark a new and complete act of creation, but only an occasional scene, taken almost at hazard, in an ever slowly changing drama.

We can clearly understand why a species when once lost should never reappear, even if the very same conditions of life, organic and inorganic, should recur. For though the offspring of one species might be adapted (and no doubt this has occurred in innumerable instances) to fill the .. place of another species in the economy of nature, and thus supplant it; yet the two forms— the old and the new— would not be identically the same; for both would almost certainly inherit different characters from their distinct progenitors, and organisms already differing would vary in a different manner. For instance, it is just possible, if all our fantail pigeons were destroyed, that fanciers ... might make a new breed hardly distinguishable from the present breed; but if the parent rock-pigeon were likewise destroyed, and under nature we have every reason to believe that .. parent-forms are generally .. supplanted and exterminated by their improved offspring, it is .. incredible that a fantail, identical with the existing breed, could be raised from any other species of pigeon, or even from any other