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the rise and progress of palaeontology-第4章

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they are dipnoi or whether they are ganoids。 



Agassiz's long and elaborate researches upon fossil fishes;

published between 1833 and 1842; led him to suggest the

existence of another kind of relation between ancient and modern

forms of life。 He observed that the oldest fishes present

many characters which recall the embryonic conditions of

existing fishes; and that; not only among fishes; but in several

groups of the invertebrata which have a long palaeontological

history; the latest forms are more modified; more specialised;

than the earlier。 The fact that the dentition of the older

tertiary ungulate and carnivorous mammals is always complete;

noticed by Professor Owen; illustrated the same generalisation。



Another no less suggestive observation was made by Mr。 Darwin;

whose personal investigations during the voyage of the

Beagle led him to remark upon the singular fact; that the

fauna; which immediately precedes that at present existing in

any geographical province of distribution; presents the same

peculiarities as its successor。 Thus; in South America and in

Australia; the later tertiary or quaternary fossils show that

the fauna which immediately preceded that of the present day

was; in the one case; as much characterised by edentates and; in

the other; by marsupials as it is now; although the species of

the older are largely different from those of the newer fauna。



However clearly these indications might point in one direction;

the question of the exact relation of the successive forms of

animal and vegetable life could be satisfactorily settled only

in one way; namely; by comparing; stage by stage; the series of

forms presented by one and the same type throughout a long

space of time。 Within the last few years this has been done

fully in the case of the horse; less completely in the case of

the other principal types of the ungulata and of the carnivora;

and all these investigations tend to one general result; namely;

that; in any given series; the successive members of that series

present a gradually increasing specialisation of structure。

That is to say; if any such mammal at present existing has

specially modified and reduced limbs or dentition and

complicated brain; its predecessors in time show less and less

modification and reduction in limbs and teeth and a less highly

developed brain。 The labours of Gaudry; Marsh; and Cope furnish

abundant illustrations of this law from the marvellous fossil

wealth of Pikermi and the vast uninterrupted series of tertiary

rocks in the territories of North America。



I will now sum up the results of this sketch of the rise and

progress of palaeontology。 The whole fabric of palaeontology is

based upon two propositions: the first is; that fossils are the

remains of animals and plants; and the second is; that the

stratified rocks in which they are found are sedimentary

deposits; and each of these propositions is founded upon the

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。











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