coveries follow one another in this almost boundless field of science; and when to this is
added the positive evidences of variation under domestication, the implied evidence to be
found in the coexistence of infinitely minute gradations of form in every branch of t h e animal
and vegetable kingdoms, and the hitherto insurmountable difficulties which have surrounded
systematists, a n d up to the present time have rendered all definitions of t h e usual expressions
of classification unsatisfactory, a good prima facie case has been made out for accepting the
proposition that all known forms of living organisms are capable of spontaneous variation
which may become hereditary. But that this capability is dormant at most times, t h a t its
exercise is an exception to the ordinary laws of nature, and that it is, in the majority of
instances, called i n to play b y a change i n t h e outward circumstances involving a wide departure
from the ordinary conditions of life, there are many equally (if not more) clear indications
throughout Xature. In other words, hereditary permanence seems to be a principle of the
law of generation, while enforced changes of condition call into play a power of variation,
dormant while those conditions remain unchanged.
The evidence furnished by geology seems to compel us either to admit t h e hypothesis of
modified descent, or hold to the idea of successive creations; though neither of t h em can in
t h e present state of the science be absolutely proved from it. That hereditary variation is
possible, and exists in the manner above stated, we fully admit; but the incalculably small
effects t h a t i t has produced in recent periods warrant grave doubts as to its being the chief,
much less t h e sole, agent in t h e origin of species : if it be the correct hypothesis, the geological
record ought t o show a continually decreasing ratio i n the number and diversity of forms of
life as we look backwards through time, culminating of course in the single primordial
form. On the other hand, if diversified creation be the true solution of t h e problem,
t h e receding geological strata should exhibit fewer and fewer intermediate forms, and continued
isolation of types, till the original parents alone were left of each group of organisms,
whether at present existing, or that have existed and are now extinct, widely differing from
each other at first in all probability, though their offspring, from numerous complex causes,
have varied considerably in adapting themselves to t h e changing conditions of life to which
they have in the course of time been exposed. Geologists must settle which of the two propositions
is best borne out by t h e facts, t h o u g h we fear t h a t these are not sufficiently decisive
as j e t to afford satisfactory proofs. The incompleteness of t h e record from lack of investigation,
and still more so from the very inconsiderable fraction of t h e whole organic remains of
past ages that has been thus preserved, will render the actual demonstration of the t r u t h or
falsity of any theory impracticable: indeed t h e evidence conveyed in t h e obtrusive appearance
of new and unexpected genera at late periods of the Earth's history is not more damaging
to the one hypothesis, than the absence of heavily charged sub-Silurian fossiliferous
deposits is to the other; and even now the forms found in the oldest strata exhibit great
diversity.
W i t h regard t o t h e origin of life, the laws of generation do not help us, for they start with
presupposing its existence; and if the inquiry is to embrace the origin of inorganic as well
as organic matter, we meet ultimately an impassable barrier—a scientific impossibility—the
production of something out of nothing. If, however, the inquiiy be limited to the origin
of living organisms only, it does not necessarily involve any thing further than a change of
condition of matter; for the presence of inorganic substance is certainly far anterior to the
first dawn of life. A time must have been when this change took place—when the breath
of life first appeared in t h e organisms on the surface of this e a r t h ; and as it has undoubtedly
occurred once, i t is w i t h i n t h e limits of possibility t h a t i t may have occurred again and
again; and it may even account for the successive and, otherwise, too sudden appearance of
new orders and families.
The majority of the experiments on which the theory of modified descent is based have
reference to animals &c. under domestication; and in enumerating these sufficient weight does
not seem to have been attached to the fact that these domestic species do not exhibit the
hereditary permanence that distinguishes true species, and that, when the disturbing influence
is removed and the former conditions of life are restored, they lose their identity and in process
of time revert to t h e original t y p e : as an instance of this the case of the dog is most notable,
and must have attracted the attention of many people in India and the East. In countries
where the wild dog still exists and where it is apparently indigenous, in India especially, as
as far as our experience goes, domesticated dogs when left to themselves tend rapidly to assimilate
in appearance to the general type of wild dog of t h e country, t h i s being brought about
partly by interbreeding with the wild dogs, and partly by degeneration of race through lack
of supervision. In this there is a most significant peculiarity, that the interbreeding does not
tend to assimilate t h e wild dog to t h e domestic, b u t t h e domestic t o t h e w i l d ; and t h e domestic
dog, though undoubtedly higher in t h e scale of organized beings, and with all the advantages
of training to aid him in t h e struggle for existence (which should, according to the theory of
natural selection, have made h im t h e dominant species), is invariably extinguished. This bears
out the idea that the domestic dog is a variety, an evidence of one phase of the law of generation
(constancy to a type), dormant for a time, reappearing with unimpaired vigour as soon
as the external disturbing influence was removed, t h e inherent capacity for adaptation ceasing
to exert itself under a recurrence to the original conditions of life. In the same way, if a
flock of the best-bred pigeons, containing pairs of t h e most diverse forms produced by selected
breeding, be left to their own resources, they soon mix promiscuously, and in a few generations
produce an anomalous race, every individual of which resembles, except in colouring,
and sometimes even in this, the original type of wild pigeon: it is sufficient to illustrate the
principle, that the anomalous forms, such as the crop of the Pouter, t h e tail of the Fantail,
and the ruff of the Jacobin, do disappear when not superintended by man. We speak of
course from a very limited experience; but, such as it is, it bears out this view of the case,
and, as far as we know, no variety a s yet produced by artificial interbreeding and selection has
exhibited that hereditary permanence which is so marked a characteristic of even the most
closely allied of the natural species, such as, for instance, Fieldfares and Thrushes, Willowwrens
and Garden W a r b l e r s ; and this alone should make us pause before attributing to
natural species precisely the same origin as we perceive domestic species to have had. A
certain degree of permanence has been obtained in some varieties of domesticated animals;