按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
way； our opponents would not be long in letting us know that
absolute proof is unattainable on any subject； that reasonable
presumption is our highest certainty； and that crying out for too
much evidence is as bad as accepting too little。 Truth is like a
photographic sensitised plate； which is equally ruined by over and
by under exposure； and the just exposure for which can never be
absolutely determined。
Surely if disuse can be credited with the vast powers involved in
Mr。 Darwin's statement that it has probably 〃been the main agent in
rendering organs rudimentary；〃 no limits are assignable to the
accumulated effects of habit； provided the effects of habit； or use
and disuse； are supposed； as Mr。 Darwin supposed them； to be
inheritable at all。 Darwinians have at length woke up to the
dilemma in which they are placed by the manner in which Mr。 Darwin
tried to sit on the two stools of use and disuse； and natural
selection of accidental variations； at the same time。 The knell of
Charles…Darwinism is rung in Mr。 Wallace's present book； and in the
general perception on the part of biologists that we must either
assign to use and disuse such a predominant share in modification as
to make it the feature most proper to be insisted on； or deny that
the modifications； whether of mind or body； acquired during a single
lifetime； are ever transmitted at all。 If they can be inherited at
all； they can be accumulated。 If they can be accumulated at all；
they can be so； for anything that appears to the contrary； to the
extent of the specific and generic differences with which we are
surrounded。 The only thing to do is to pluck them out root and
branch： they are as a cancer which； if the smallest fibre be left
unexcised； will grow again； and kill any system on to which it is
allowed to fasten。 Mr。 Wallace； therefore； may well be excused if
he casts longing eyes towards Weismannism。
And what was Mr。 Darwin's system？ Who can make head or tail of the
inextricable muddle in which he left it？ The 〃Origin of Species〃 in
its latest shape is the reduction of hedging to an absurdity。 How
did Mr。 Darwin himself leave it in the last chapter of the last
edition of the 〃Origin of Species〃？ He wrote：…
〃I have now recapitulated the facts and considerations which have
thoroughly convinced me that species have been modified during a
long course of descent。 This has been effected chiefly through the
natural selection of numerous； successive； slight； favourable
variations； aided in an important manner by the inherited effects of
the use and disuse of parts； and in an unimportant mannerthat is；
in relation to adaptive structures whether past or presentby the
direct action of external conditions； and by variations which seem
to us in our ignorance to arise spontaneously。 It appears that I
formerly underrated the frequency and value of these latter forms of
variation； as leading to permanent modifications of structure
independently of natural selection。〃
The 〃numerous； successive； slight； favourable variations〃 above
referred to are intended to be fortuitous； accidental； spontaneous。
It is the essence of Mr。 Darwin's theory that this should be so。
Mr。 Darwin's solemn statement； therefore； of his theory； after he
had done his best or his worst with it； is； when stripped of
surplusage； as follows：…
〃The modification of species has been mainly effected by
accumulation of spontaneous variations； it has been aided in an
important manner by accumulation of variations due to use and
disuse； and in an unimportant manner by spontaneous variations； I do
not even now think that spontaneous variations have been very
important； but I used once to think them less important than I do
now。〃
It is a discouraging symptom of the age that such a system should
have been so long belauded； and it is a sign of returning
intelligence that even he who has been more especially the alter ego
of Mr。 Darwin should have felt constrained to close the chapter of
Charles…Darwinism as a living theory； and relegate it to the
important but not very creditable place in history which it must
henceforth occupy。 It is astonishing； however； that Mr。 Wallace
should have quoted the extract from the 〃Origin of Species〃 just
given； as he has done on p。 412 of his 〃Darwinism；〃 without
betraying any sign that he has caught its driftlessnessfor drift；
other than a desire to hedge； it assuredly has not got。 The battle
now turns on the question whether modifications of either structure
or instinct due to use or disuse are ever inherited； or whether they
are not。 Can the effects of habit be transmitted to progeny at all？
We know that more usually they are not transmitted to any
perceptible extent； but we believe also that occasionally； and
indeed not infrequently； they are inherited and even intensified。
What are our grounds for this opinion？ It will be my object to put
these forward in the following number of the Universal Review。
THE DEADLOCK IN DARWINISMPART II ｛29｝
At the close of my article in last month's number of the Universal
Review； I said I would in this month's issue show why the opponents
of Charles…Darwinism believe the effects of habits acquired during
the lifetime of a parent to produce an effect on their subsequent
offspring； in spite of the fact that we can rarely find the effect
in any one generation； or even in several； sufficiently marked to
arrest our attention。
I will now show that offspring can be； and not very infrequently is；
affected by occurrences that have produced a deep impression on the
parent organismthe effect produced on the offspring being such as
leaves no doubt that it is to be connected with the impression
produced on the parent。 Having thus established the general
proposition； I will proceed to the more particular onethat habits；
involving use and disuse of special organs； with the modifications
of structure thereby engendered； produce also an effect upon
offspring； which； though seldom perceptible as regards structure in
a single； or even in several generations； is nevertheless capable of
being accumulated in successive generations till it amounts to
specific and generic difference。 I have found the first point as
much as I can treat within the limits of this present article； and
will avail myself of the hospitality of the Universal Review next
month to deal with the second。
The proposition which I have to defend is one which no one till
recently would have questioned； and even now； those who look most
askance at it do not venture to dispute it unreservedly； they every
now and then admit it as conceivable； and even in some cases
probable； nevertheless they seek to minimise it； and to make out
that there is little or no connection between the great mass of the
cells of which the body is composed； and those cells that are alone
capable of reproducing the entire organism。 The tendency is to
assign to these last a life of their own； apart from； and
unconnected with that of the other cells of the body； and to cheapen
all evidence that tends to prove any response on their part to the
past history of the individual； and hence ultimately of the race。
Professor Weismann is the foremost exponent of those who take this
line。 He has naturally been welcomed by English Charles…Darwinians；
for if his view can be sustained； then it can be contended that use
and disuse produce no transmissible effect； and the ground is cut
from under Lamarck's feet； if； on the other hand； his view is
unfounded； the Lamarckian reaction； already strong； will gain still
further strength。 The issue； therefore； is important； and is being
fiercely contested by those who have invested their all of
reputation for discernment in Charles…Darwinian securities。
Professor Weismann's theory is； that at every new birth a part of
the substance which proceeds from parents and which goes to form the
new embryo is not used up in forming the new animal； but remains
apart to generate the germ…cellsor perhaps I should say 〃germ…
plasm〃which the new animal itself will in due course issue。
Contrasting the generally received view with his own； Professor
Weismann says that according to the first of these 〃the organism
produces germ…cells afresh again and again； and that it produces
them entirely from its own substance。〃 While by the second 〃the
germ…cells are no longer looked upon as the product of the parent's
body； at least as far as their essential partthe specific germ…
plasmis concerned； they are rather considered as something which
is to be placed in contrast with the tout ensemble of the cells
which make up the parent's body； and the germ…cells of succeeding
generations stand in a similar relation to one another as a series
of generations of unicellular organisms arising by a continued
process of cell…division。〃 ｛30｝
On another page he writes：…
〃I believe that heredity depends upon the fact that a small portion
of the effective substance of the germ； the germ…plasm； remains
unchanged during the development of the ovum into an organism； and
that this part of the germ…plasm serves as a foundation from which
the germ…cells of the new organi