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same axiom； that like effects imply like causes。 If there is any
cause competent to produce a fossil stem； or shell； or bone；
except a living being； then palaeontology has no foundation；
if the stratification of the rocks is not the effect of such
causes as at present produce stratification； we have no means of
judging of the duration of past time； or of the order in which
the forms of life have succeeded one another。 But if these two
propositions are granted； there is no escape； as it appears to
me； from three very important conclusions。 The first is that
living matter has existed upon the earth for a vast length of
time； certainly for millions of years。 The second is that；
during this lapse of time； the forms of living matter have
undergone repeated changes； the effect of which has been that
the animal and vegetable population； at any period of the
earth's history； contains certain species which did not exist at
some antecedent period； and others which ceased to exist at some
subsequent period。 The third is that； in the case of many groups
of mammals and some of reptiles； in which one type can be
followed through a considerable extent of geological time； the
series of different forms by which the type is represented； at
successive intervals of this time； is exactly such as it would
be； if they had been produced by the gradual modification of the
earliest forms of the series。 These are facts of the history of
the earth guaranteed by as good evidence as any facts in
civil history。
Hitherto I have kept carefully clear of all the hypotheses to
which men have at various times endeavoured to fit the facts of
palaeontology； or by which they have endeavoured to connect
as many of these facts as they happened to be acquainted with。
I do not think it would be a profitable employment of our time
to discuss conceptions which doubtless have had their
justification and even their use； but which are now obviously
incompatible with the well…ascertained truths of palaeontology。
At present these truths leave room for only two hypotheses。
The first is that； in the course of the history of the earth；
innumerable species of animals and plants have come into
existence； independently of one another； innumerable times。
This； of course； implies either that spontaneous generation on
the most astounding scale； and of animals such as horses and
elephants； has been going on； as a natural process； through all
the time recorded by the fossiliferous rocks； or it necessitates
the belief in innumerable acts of creation repeated innumerable
times。 The other hypothesis is； that the successive species of
animals and plants have arisen； the later by the gradual
modification of the earlier。 This is the hypothesis of
evolution； and the palaeontological discoveries of the last
decade are so completely in accordance with the requirements of
this hypothesis that； if it had not existed； the palaeontologist
would have had to invent it。
I have always had a certain horror of presuming to set a limit
upon the possibilities of things。 Therefore I will not venture
to say that it is impossible that the multitudinous species of
animals and plants may have been produced； one separately
from the other； by spontaneous generation； nor that it is
impossible that they should have been independently originated
by an endless succession of miraculous creative acts。 But I must
confess that both these hypotheses strike me as so astoundingly
improbable； so devoid of a shred of either scientific or
traditional support； that even if there were no other evidence
than that of palaeontology in its favour； I should feel
compelled to adopt the hypothesis of evolution。 Happily； the
future of palaeontology is independent of all hypothetical
considerations。 Fifty years hence； whoever undertakes to record
the progress of palaeontology will note the present time as the
epoch in which the law of succession of the forms of the higher
animals was determined by the observation of palaeontological
facts。 He will point out that； just as Steno and as Cuvier were
enabled from their knowledge of the empirical laws of co…
existence of the parts of animals to conclude from a part to the
whole； so the knowledge of the law of succession of forms
empowered their successors to conclude； from one or two terms of
such a succession； to the whole series； and thus to divine the
existence of forms of life； of which； perhaps； no trace remains；
at epochs of inconceivable remoteness in the past。
FOOTNOTES
（1） De Solidoiintra Solidum； p。5〃Dato corpore certa
figura praedito et juxta leges naturae producto； in ipso corpore
argumenta invenire locum et modum productionis detegentia。〃
（2） 〃Corpora sibi invicem omnino similia simili etiam modo
producta sunt。〃
（3） Sir J。 D。 Hooker。
End