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lectures on evolution-第2章

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childhood; that this hypothesis owes its general wide diffusion

as one of the current beliefs of English…speaking people。 If you

turn to the seventh book of 〃Paradise Lost;〃 you will find there

stated the hypothesis to which I refer; which is briefly this:

That this visible universe of ours came into existence at no

great distance of time from the present; and that the parts of

which it is composed made their appearance; in a certain

definite order; in the space of six natural days; in such a

manner that; on the first of these days; light appeared; that;

on the second; the firmament; or sky; separated the waters

above; from the waters beneath the firmament; that; on the third

day; the waters drew away from the dry land; and upon it a

varied vegetable life; similar to that which now exists; made

its appearance; that the fourth day was signalised by the

apparition of the sun; the stars; the moon; and the planets;

that; on the fifth day; aquatic animals originated within the

waters; that; on the sixth day; the earth gave rise to our four…

footed terrestrial creatures; and to all varieties of

terrestrial animals except birds; which had appeared on the

preceding day; and; finally; that man appeared upon the earth;

and the emergence of the universe from chaos was finished。

Milton tells us; without the least ambiguity; what a spectator

of these marvellous occurrences would have witnessed。 I doubt

not that his poem is familiar to all of you; but I should like

to recall one passage to your minds; in order that I may be

justified in what I have said regarding the perfectly concrete;

definite; picture of the origin of the animal world which Milton

draws。 He says:



〃The sixth; and of creation last; arose

With evening harp and matin; when God said;

'Let the earth bring forth soul living in her kind;

Cattle and creeping things; and beast of the earth。

Each in their kind!' The earth obeyed; and; straight

Opening her fertile womb; teemed at a birth

Innumerous living creatures; perfect forms;

Limbed and full…grown。 Out of the ground uprose;

As from his lair; the wild beast; where he wons

In forest wild; in thicket; brake; or den;

Among the trees in pairs they rose; they walked;

The cattle in the fields and meadows green;

Those rare and solitary; these in flocks

Pasturing at once; and in broad herds upsprung。

The grassy clods now calved; now half appears

The tawny lion; pawing to get free

His hinder partsthen springs; as broke from bonds;

And rampant shakes his brinded mane; the ounce;

The libbard; and the tiger; as the mole

Rising; the crumbled earth above them threw

In hillocks; the swift stag from underground

Bore up his branching head; scarce from his mould

Behemoth; biggest born of earth; upheaved

His vastness; fleeced the flocks and bleating rose

As plants; ambiguous between sea and land;

The river…horse and scaly crocodile。

At once came forth whatever creeps the ground;

Insect or worm。〃



There is no doubt as to the meaning of this statement; nor as to

what a man of Milton's genius expected would have been actually

visible to an eye…witness of this mode of origination of

living things。



The third hypothesis; or the hypothesis of evolution; supposes

that; at any comparatively late period of past time; our

imaginary spectator would meet with a state of things very

similar to that which now obtains; but that the likeness of the

past to the present would gradually become less and less; in

proportion to the remoteness of his period of observation from

the present day; that the existing distribution of mountains and

plains; of rivers and seas; would show itself to be the product

of a slow process of natural change operating upon more and more

widely different antecedent conditions of the mineral frame…work

of the earth; until; at length; in place of that frame…work; he

would behold only a vast nebulous mass; representing the

constituents of the sun and of the planetary bodies。 Preceding

the forms of life which now exist; our observer would see

animals and plants; not identical with them; but like them;

increasing their differences with their antiquity and; at the

same time; becoming simpler and simpler; until; finally; the

world of life would present nothing but that undifferentiated

protoplasmic matter which; so far as our present knowledge goes;

is the common foundation of all vital activity。



The hypothesis of evolution supposes that in all this vast

progression there would be no breach of continuity; no point at

which we could say 〃This is a natural process;〃 and 〃This is not

a natural process;〃 but that the whole might be compared to that

wonderful operation of development which may be seen going on

every day under our eyes; in virtue of which there arises; out

of the semi…fluid comparatively homogeneous substance which we

call an egg; the complicated organisation of one of the higher

animals。 That; in a few words; is what is meant by the

hypothesis of evolution。



I have already suggested that; in dealing with these three

hypotheses; in endeavouring to form a judgment as to which of

them is the more worthy of belief; or whether none is worthy of

beliefin which case our condition of mind should be that

suspension of judgment which is so difficult to all but trained

intellectswe should be indifferent to all a priori

considerations。 The question is a question of historical fact。

The universe has come into existence somehow or other; and the

problem is; whether it came into existence in one fashion; or

whether it came into existence in another; and; as an essential

preliminary to further discussion; permit me to say two or three

words as to the nature and the kinds of historical evidence。



The evidence as to the occurrence of any event in past time may

be ranged under two heads which; for convenience' sake; I will

speak of as testimonial evidence and as circumstantial evidence。

By testimonial evidence I mean human testimony; and by

circumstantial evidence I mean evidence which is not human

testimony。 Let me illustrate by a familiar example what I

understand by these two kinds of evidence; and what is to be

said respecting their value。



Suppose that a man tells you that he saw a person strike another

and kill him; that is testimonial evidence of the fact of

murder。 But it is possible to have circumstantial evidence of

the fact of murder; that is to say; you may find a man dying

with a wound upon his head having exactly the form and character

of the wound which is made by an axe; and; with due care in

taking surrounding circumstances into account; you may conclude

with the utmost certainty that the man has been murdered;

that his death is the consequence of a blow inflicted by another

man with that implement。 We are very much in the habit of

considering circumstantial evidence as of less value than

testimonial evidence; and it may be that; where the

circumstances are not perfectly clear and intelligible; it is a

dangerous and unsafe kind of evidence; but it must not be

forgotten that; in many cases; circumstantial is quite as

conclusive as testimonial evidence; and that; not unfrequently;

it is a great deal weightier than testimonial evidence。

For example; take the case to which I referred just now。

The circumstantial evidence may be better and more convincing

than the testimonial evidence; for it may be impossible; under

the conditions that I have defined; to suppose that the man met

his death from any cause but the violent blow of an axe wielded

by another man。 The circumstantial evidence in favour of a

murder having been committed; in that case; is as complete and

as convincing as evidence can be。 It is evidence which is open

to no doubt and to no falsification。 But the testimony of a

witness is open to multitudinous doubts。 He may have been

mistaken。 He may have been actuated by malice。 It has constantly

happened that even an accurate man has declared that a thing has

happened in this; that; or the other way; when a careful

analysis of the circumstantial evidence has shown that it did

not happen in that way; but in some other way。



We may now consider the evidence in favour of or against the

three hypotheses。 Let me first direct your attention to what is

to be said about the hypothesis of the eternity of the state of

things in which we now live。 What will first strike you is; that

it is a hypothesis which; whether true or false; is not capable

of verification by any evidence。 For; in order to obtain either

circumstantial or testimonial evidence sufficient to prove the

eternity of duration of the present state of nature; you must

have an eternity of witnesses or an infinity of circumstances;

and neither of these is attainable。 It is utterly impossible

that such evidence should be carried beyond a certain point of

time; and all that could be said; at most; would be; that s
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