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Darwiniana

T >> Thomas Henry Huxley >> Darwiniana




I do not know what Mr. Godwin Austin would say comes next, but probably
rocks containing more ammonites, and more ichthyosauria and plesiosauria,
with a vast number of other things; and under that I should meet with yet
older rocks containing numbers of strange shells and fishes; and in thus
passing from the surface to the lowest depths of the earth's crust, the
forms of animal life and vegetable life which I should meet with in the
successive beds would, looking at them broadly, be the more different the
further that I went down. Or, in other words, inasmuch as we started with
the clear principle, that in a series of naturally-disposed mud beds the
lowest are the oldest, we should come to this result, that the further we
go back in time the more difference exists between the animal and vegetable
life of an epoch and that which now exists. That was the conclusion to
which I wished to bring you at the end of this lecture.



III. THE METHOD BY WHICH THE CAUSES OF THE PRESENT AND PAST CONDITIONS OF
ORGANIC NATURE ARE TO BE DISCOVERED;--THE ORIGINATION OF LIVING BEINGS


In the two preceding lectures I have endeavoured to indicate to you the
extent of the subject-matter of the inquiry upon which we are engaged; and
having thus acquired some conception of the past and present phenomena of
organic nature, I must now turn to that which constitutes the great problem
which we have set before ourselves;--I mean, the question of what knowledge
we have of the causes of these phenomena of organic nature, and how such
knowledge is obtainable.

Here, on the threshold of the inquiry, an objection meets us. There are in
the world a number of extremely worthy, well-meaning persons, whose
judgments and opinions are entitled to the utmost respect on account of
their sincerity, who are of opinion that vital phenomena, and especially
all questions relating to the origin of vital phenomena, are questions
quite apart from the ordinary run of inquiry, and are, by their very
nature, placed out of our reach. They say that all these phenomena
originated miraculously, or in some way totally different from the ordinary
course of nature, and that therefore they conceive it to be futile, not to
say presumptuous, to attempt to inquire into them.

To such sincere and earnest persons, I would only say, that a question of
this kind is not to be shelved upon theoretical or speculative grounds. You
may remember the story of the Sophist who demonstrated to Diogenes in the
most complete and satisfactory manner that he could not walk; that, in
fact, all motion was an impossibility; and that Diogenes refuted him by
simply getting up and walking round his tub. So, in the same way, the man
of science replies to objections of this kind, by simply getting up and
walking onward, and showing what science has done and is doing---by
pointing to that immense mass of facts which have been ascertained as
systematised under the forms of the great doctrines of morphology, of
development, of distribution, and the like. He sees an enormous mass of
facts and laws relating to organic beings, which stand on the same good
sound foundation as every other natural law. With this mass of facts and
laws before us, therefore, seeing that, as far as organic matters have
hitherto been accessible and studied, they have shown themselves capable of
yielding to scientific investigation, we may accept this as proof that
order and law reign there as well as in the rest of Nature. The man of
science says nothing to objectors of this sort, but supposes that we can
and shall walk to a knowledge of the origin of organic nature, in the same
way that we have walked to a knowledge of the laws and principles of the
inorganic world.

But there are objectors who say the same from ignorance and ill-will. To
such I would reply that the objection comes ill from them, and that the
real presumption, I may almost say the real blasphemy, in this matter, is
in the attempt to limit that inquiry into the causes of phenomena, which is
the source of all human blessings, and from which has sprung all human
prosperity and progress; for, after all, we can accomplish comparatively
little; the limited range of our own faculties bounds us on every
side,--the field of our powers of observation is small enough, and he who
endeavours to narrow the sphere of our inquiries is only pursuing a course
that is likely to produce the greatest harm to his fellow-men.

But now, assuming, as we all do, I hope, that these phenomena are properly
accessible to inquiry, and setting out upon our search into the causes of
the phenomena of organic nature, or at any rate, setting out to discover
how much we at present know upon these abstruse matters, the question
arises as to what is to be our course of proceeding, and what method we
must lay down for our guidance. I reply to that question, that our method
must be exactly the same as that which is pursued in any other scientific
inquiry, the method of scientific investigation being the same for all
orders of facts and phenomena whatsoever.

I must dwell a little on this point, for I wish you to leave this room with
a very clear conviction that scientific investigation is not, as many
people seem to suppose, some kind of modern black art. I say that you might
easily gather this impression from the manner in which many persons speak
of scientific inquiry, or talk about inductive and deductive philosophy, or
the principles of the "Baconian philosophy." I do protest that, of the vast
number of cants in this world, there are none, to my mind, so contemptible
as the pseudo-scientific cant which is talked about the "Baconian
philosophy."

To hear people talk about the great Chancellor--and a very great man he
certainly was,--you would think that it was he who had invented science,
and that there was no such thing as sound reasoning before the time of
Queen Elizabeth! Of course you say, that cannot possibly be true; you
perceive, on a moment's reflection, that such an idea is absurdly wrong,
and yet, so firmly rooted is this sort of impression,--I cannot call it an
idea, or conception,--the thing is too absurd to be entertained,--but so
completely does it exist at the bottom of most men's minds, that this has
been a matter of observation with me for many years past. There are many
men who, though knowing absolutely nothing of the subject with which they
may be dealing, wish, nevertheless, to damage the author of some view with
which they think fit to disagree. What they do, then, is not to go and
learn something about the subject, which one would naturally think the best
way of fairly dealing with it; but they abuse the originator of the view
they question, in a general manner, and wind up by saying that, "After all,
you know, the principles and method of this author are totally opposed to
the canons of the Baconian philosophy." Then everybody applauds, as a
matter of course, and agrees that it must be so. But if you were to stop
them all in the middle of their applause, you would probably find that
neither the speaker nor his applauders could tell you how or in what way it
was so; neither the one nor the other having the slightest idea of what
they mean when they speak of the "Baconian philosophy."

You will understand, I hope, that I have not the slightest desire to join
in the outcry against either the morals, the intellect, or the great genius
of Lord Chancellor Bacon. He was undoubtedly a very great man, let people
say what they will of him; but notwithstanding all that he did for
philosophy, it would be entirely wrong to suppose that the methods of
modern scientific inquiry originated with him, or with his age; they
originated with the first man, whoever he was; and indeed existed long
before him, for many of the essential processes of reasoning are exerted by
the higher order of brutes as completely and effectively as by ourselves.
We see in many of the brute creation the exercise of one, at least, of the
same powers of reasoning as that which we ourselves employ.

The method of scientific investigation is nothing but the expression of the
necessary mode of working of the human mind. It is simply the mode at which
all phenomena are reasoned about, rendered precise and exact. There is no
more difference, but there is just the same kind of difference, between the
mental operations of a man of science and those of an ordinary person, as
there is between the operations and methods of a baker or of a butcher
weighing out his goods in common scales, and the operations of a chemist in
performing a difficult and complex analysis by means of his balance and
finely-graduated weights. It is not that the action of the scales in the
one case, and the balance in the other, differ in the principles of their
construction or manner of working; but the beam of one is set on an
infinitely finer axis than the other, and of course turns by the addition
of a much smaller weight.

You will understand this better, perhaps, if I give you some familiar
example. You have all heard it repeated, I dare say, that men of science
work by means of induction and deduction, and that by the help of these
operations, they, in a sort of sense, wring from Nature certain other
things, which are called natural laws, and causes, and that out of these,
by some cunning skill of their own, they build up hypotheses and theories.
And it is imagined by many, that the operations of the common mind can be
by no means compared with these processes, and that they have to be
acquired by a sort of special apprenticeship to the craft. To hear all
these large words, you would think that the mind of a man of science must
be constituted differently from that of his fellow men; but if you will not
be frightened by terms, you will discover that you are quite wrong, and
that all these terrible apparatus are being used by yourselves every day
and every hour of your lives.

There is a well-known incident in one of Molière's plays, where the author
makes the hero express unbounded delight on being told that he had been
talking prose during the whole of his life. In the same way, I trust, that
you will take comfort, and be delighted with yourselves, on the discovery
that you have been acting on the principles of inductive and deductive
philosophy during the same period. Probably there is not one here who has
not in the course of the day had occasion to set in motion a complex train
of reasoning, of the very same kind, though differing of course in degree,
as that which a scientific man goes through in tracing the causes of
natural phenomena.

A very trivial circumstance will serve to exemplify this. Suppose you go
into a fruiterer's shop, wanting an apple,--you take up one, and, on biting
it, you find it is sour; you look at it, and see that it is hard and green.
You take up another one, and that too is hard, green, and sour. The shopman
offers you a third; but, before biting it, you examine it, and find that it
is hard and green, and you immediately say that you will not have it, as it
must be sour, like those that you have already tried.

Nothing can be more simple than that, you think; but if you will take the
trouble to analyse and trace out into its logical elements what has been
done by the mind, you will be greatly surprised. In the first place, you
have performed the operation of induction. You found that, in two
experiences, hardness and greenness in apples went together with sourness.
It was so in the first case, and it was confirmed by the second. True, it
is a very small basis, but still it is enough to make an induction from;
you generalise the facts, and you expect to find sourness in apples where
you get hardness and greenness. You found upon that a general law, that all
hard and green apples are sour; and that, so far as it goes, is a perfect
induction. Well, having got your natural law in this way, when you are
offered another apple which you find is hard and green, you say, "All hard
and green apples are sour; this apple is hard and green, therefore this
apple is sour." That train of reasoning is what logicians call a syllogism,
and has all its various parts and terms,--its major premiss, its minor
premiss, and its conclusion. And, by the help of further reasoning, which,
if drawn out, would have to be exhibited in two or three other syllogisms,
you arrive at your final determination, "I will not have that apple." So
that, you see, you have, in the first place, established a law by
induction, and upon that you have founded a deduction, and reasoned out the
special conclusion of the particular case. Well now, suppose, having got
your law, that at some time afterwards, you are discussing the qualities of
apples with a friend: you will say to him, "It is a very curious
thing,--but I find that all hard and green apples are sour!" Your friend
says to you, "But how do you know that?" You at once reply, "Oh, because I
have tried them over and over again, and have always found them to be so."
Well, if we were talking science instead of common sense, we should call
that an experimental verification. And, if still opposed, you go further,
and say, "I have heard from the people in Somersetshire and Devonshire,
where a large number of apples are grown, that they have observed the same
thing. It is also found to be the case in Normandy, and in North America.
In short, I find it to be the universal experience of mankind wherever
attention has been directed to the subject." Whereupon, your friend, unless
he is a very unreasonable man, agrees with you, and is convinced that you
are quite right in the conclusion you have drawn. He believes, although
perhaps he does not know he believes it, that the more extensive
verifications are,--that the more frequently experiments have been made,
and results of the same kind arrived at,--that the more varied the
conditions under which the same results are attained, the more certain is
the ultimate conclusion, and he disputes the question no further. He sees
that the experiment has been tried under all sorts of conditions, as to
time, place, and people, with the same result; and he says with you,
therefore, that the law you have laid down must be a good one, and he must
believe it.

In science we do the same thing;--the philosopher exercises precisely the
same faculties, though in a much more delicate manner. In scientific
inquiry it becomes a matter of duty to expose a supposed law to every
possible kind of verification, and to take care, moreover, that this is
done intentionally, and not left to a mere accident, as in the case of the
apples. And in science, as in common life, our confidence in a law is in
exact proportion to the absence, of variation in the result of our
experimental verifications. For instance, if you let go your grasp of an
article you may have in your hand, it will immediately fall to the ground.
That is a very common verification of one of the best established laws of
nature--that of gravitation. The method by which men of science establish
the existence of that law is exactly the same as that by which we have
established the trivial proposition about the sourness of hard and green
apples. But we believe it in such an extensive, thorough, and unhesitating
manner because the universal experience of mankind verifies it, and we can
verify it ourselves at any time; and that is the strongest possible
foundation on which any natural law can rest.

So much, then, by way of proof that the method of establishing laws in
science is exactly the same as that pursued in common life. Let us now turn
to another matter (though really it is but another phase of the same
question), and that is, the method by which, from the relations of certain
phenomena, we prove that some stand in the position of causes towards the
others.

I want to put the case clearly before you, and I will therefore show you
what I mean by another familiar example. I will suppose that one of you, on
coming down in the morning to the parlour of your house, finds that a
tea-pot and some spoons which had been left in the room on the previous
evening are gone,--the window is open, and you observe the mark of a dirty
hand on the window-frame, and perhaps, in addition to that, you notice the
impress of a hob-nailed shoe on the gravel outside. All these phenomena
have struck your attention instantly, and before two seconds have passed
you say, "Oh, somebody has broken open the window, entered the room, and
run off with the spoons and the tea-pot!" That speech is out of your mouth
in a moment. And you will probably add, "I know there has; I am quite sure
of it!" You mean to say exactly what you know; but in reality you are
giving expression to what is, in all essential particulars, an hypothesis.
You do not _know_ it at all; it is nothing but an hypothesis rapidly
framed in your own mind. And it is an hypothesis founded on a long train of
inductions and deductions.

What are those inductions and deductions, and how have you got at this
hypothesis? You have observed, in the first place, that the window is open;
but by a train of reasoning involving many inductions and deductions, you
have probably arrived long before at the general law--and a very good one
it is--that windows do not open of themselves; and you therefore conclude
that something has opened the window. A second general law that you have
arrived at in the same way is, that tea-pots and spoons do not go out of a
window spontaneously, and you are satisfied that, as they are not now where
you left them, they have been removed. In the third place, you look at the
marks on the window-sill, and the shoe-marks outside, and you say that in
all previous experience the former kind of mark has never been produced by
anything else but the hand of a human being; and the same experience shows
that no other animal but man at present wears shoes with hob-nails in them
such as would produce the marks in the gravel. I do not know, even if we
could discover any of those "missing links" that are talked about, that
they would help us to any other conclusion! At any rate the law which
states our present experience is strong enough for my present purpose. You
next reach the conclusion, that as these kinds of marks have not been left
by any other animals than men, or are liable to be formed in any other way
than by a man's hand and shoe, the marks in question have been formed by a
man in that way. You have, further, a general law, founded on observation
and experience, and that, too, is, I am sorry to say, a very universal and
unimpeachable one,--that some men are thieves; and you assume at once from
all these premisses--and that is what constitutes your hypothesis--that the
man who made the marks outside and on the window-sill, opened the window,
got into the room, and stole your tea-pot and spoons. You have now arrived
at a _vera causa_;--you have assumed a cause which, it is plain, is
competent to produce all the phenomena you have observed. You can explain
all these phenomena only by the hypothesis of a thief. But that is a
hypothetical conclusion, of the justice of which you have no absolute proof
at all; it is only rendered highly probable by a series of inductive and
deductive reasonings.

I suppose your first action, assuming that you are a man of ordinary common
sense, and that you have established this hypothesis to your own
satisfaction, will very likely be to go off for the police, and set them on
the track of the burglar, with the view to the recovery of your property.
But just as you are starting with this object, some person comes in, and on
learning what you are about, says, "My good friend, you are going on a
great deal too fast. How do you know that the man who really made the marks
took the spoons? It might have been a monkey that took them, and the man
may have merely looked in afterwards." You would probably reply, "Well,
that is all very well, but you see it is contrary to all experience of the
way tea-pots and spoons are abstracted; so that, at any rate, your
hypothesis is less probable than mine." While you are talking the thing
over in this way, another friend arrives, one of that good kind of people
that I was talking of a little while ago. And he might say, "Oh, my dear
sir, you are certainly going on a great deal too fast. You are most
presumptuous. You admit that all these occurrences took place when you were
fast asleep, at a time when you could not possibly have known anything
about what was taking place. How do you know that the laws of Nature are
not suspended during the night? It may be that there has been some kind of
supernatural interference in this case." In point of fact, he declares that
your hypothesis is one of which you cannot at all demonstrate the truth,
and that you are by no means sure that the laws of Nature are the same when
you are asleep as when you are awake.

Well, now, you cannot at the moment answer that kind of reasoning. You feel
that your worthy friend has you somewhat at a disadvantage. You will feel
perfectly convinced in your own mind, however, that you are quite right,
and you say to him, "My good friend, I can only be guided by the natural
probabilities of the case, and if you will be kind enough to stand aside
and permit me to pass, I will go and fetch the police." Well, we will
suppose that your journey is successful, and that by good luck you meet
with a policeman; that eventually the burglar is found with your property
on his person, and the marks correspond to his hand and to his boots.
Probably any jury would consider those facts a very good experimental
verification of your hypothesis, touching the cause of the abnormal
phenomena observed in your parlour, and would act accordingly.

Now, in this suppositious case, I have taken phenomena of a very common
kind, in order that you might see what are the different steps in an
ordinary process of reasoning, if you will only take the trouble to analyse
it carefully. All the operations I have described, you will see, are
involved in the mind of any man of sense in leading him to a conclusion as
to the course he should take in order to make good a robbery and punish the
offender. I say that you are led, in that case, to your conclusion by
exactly the same train of reasoning as that which a man of science pursues
when he is endeavouring to discover the origin and laws of the most occult
phenomena. The process is, and always must be, the same; and precisely the
same mode of reasoning was employed by Newton and Laplace in their
endeavours to discover and define the causes of the movements of the
heavenly bodies, as you, with your own common sense, would employ to detect
a burglar. The only difference is, that the nature of the inquiry being
more abstruse, every step has to be most carefully watched, so that there
may not be a single crack or flaw in your hypothesis. A flaw or crack in
many of the hypotheses of daily life may be of little or no moment as
affecting the general correctness of the conclusions at which we may
arrive; but, in a scientific inquiry, a fallacy, great or small, is always
of importance, and is sure to be in the long run constantly productive of
mischievous, if not fatal results.

Do not allow yourselves to be misled by the common notion that an
hypothesis is untrustworthy simply because it is an hypothesis. It is often
urged, in respect to some scientific conclusion, that, after all, it is
only an hypothesis. But what more have we to guide us in nine-tenths of the
most important affairs of daily life than hypotheses, and often very
ill-based ones? So that in science, where the evidence of an hypothesis is
subjected to the most rigid examination, we may rightly pursue the same
course. You may have hypotheses and hypotheses. A man may say, if he likes,
that the moon is made of green cheese: that is an hypothesis. But another
man, who has devoted a great deal of time and attention to the subject, and
availed himself of the most powerful telescopes and the results of the
observations of others, declares that in his opinion it is probably
composed of materials very similar to those of which our own earth is made
up: and that is also only an hypothesis. But I need not tell you that there
is an enormous difference in the value of the two hypotheses. That one
which is based on sound scientific knowledge is sure to have a
corresponding value; and that which is a mere hasty random guess is likely
to have but little value. Every great step in our progress in discovering
causes has been made in exactly the same way as that which I have detailed
to you. A person observing the occurrence of certain facts and phenomena
asks, naturally enough, what process, what kind of operation known to occur
in Nature applied to the particular case, will unravel and explain the
mystery? Hence you have the scientific hypothesis; and its value will be
proportionate to the care and completeness with which its basis had been
tested and verified. It is in these matters as in the commonest affairs of
practical life: the guess of the fool will be folly, while the guess of the
wise man will contain wisdom. In all cases, you see that the value of the
result depends on the patience and faithfulness with which the investigator
applies to his hypothesis every possible kind of verification.

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