St. George Stock - "Deductive Logic"

Emile Zola - "L'Assommoir"

Herman Gastrell Seely - "A Son of the City"

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More Letters of Charles Darwin Volume I

C >> Charles Darwin >> More Letters of Charles Darwin Volume I




12. Let us now consider the more difficult case of two allied species A,
B, in the same area, half the individuals of each (As, Bs) being absolutely
sterile, the other half (Af, Bf) being partially fertile: will As, Bs
ultimately exterminate Af, Bf?

13. To avoid complication, it must be granted, that between As and Bs no
cross-unions take place, while between Af and Bf cross-unions are as
frequent as direct unions, though much less fertile. We must also leave
out of consideration crosses between As and Af, Bs and Bf, with their
various approaches to sterility, as I believe they will not affect the
final result, although they will greatly complicate the problem.

14. In the first generation there will result: 1st, The pure progeny of
As and Bs; 2nd, The pure progeny of Af and of Bf; and 3rd, The hybrid
progeny of Af, Bf.

15. Supposing that, in ordinary years, the increased constitutional vigour
of the hybrids exactly counterbalances their imperfect adaptations to
conditions, there will be in the second generation, besides these three
classes, hybrids of the second degree between the first hybrids and Af and
Bf respectively. In succeeding generations there will be hybrids of all
degrees, varying between the first hybrids and the almost pure types of Af
and Bf.

16. Now, if at first the number of individuals of As, Bs, Af and Bf were
equal, and year after year the total number continues stationary, I think
it can be proved that, while half will be the pure progeny of As and Bs,
the other half will become more and more hybridised, until the whole will
be hybrids of various degrees.

17. Now, this hybrid and somewhat intermediate race cannot be so well
adapted to the conditions of life as the two pure species, which have been
formed by the minute adaptation to conditions through Natural Selection;
therefore, in a severe struggle for existence, the hybrids must succumb,
especially as, by hypothesis, their fertility would not be so great as that
of the two pure species.

18. If we were to take into consideration the unions of As with Af and Bs
with Bf, the results would become very complicated, but it must still lead
to there being a number of pure forms entirely derived from As and Bs, and
of hybrid forms mainly derived from Af and Bf; and the result of the
struggle of these two sets of individuals cannot be doubtful.

19. If these arguments are sound, it follows that sterility may be
accumulated and increased, and finally made complete by Natural Selection,
whether the sterile varieties originate together in a definite portion of
the area occupied by the two species, or occur scattered over the whole
area. (211/4. The first part of this discussion should be considered
alone, as it is both more simple and more important. I now believe that
the utility, and therefore the cause of sterility between species, is
during the process of differentiation. When species are fully formed, the
occasional occurrence of hybrids is of comparatively small importance, and
can never be a danger to the existence of the species. A.R.W. (1899).)

P.S.--In answer to the objection as to the unequal sterility of reciprocal
crosses ("Variation, etc." Volume II., page 186) I reply that, as far as it
went, the sterility of one cross would be advantageous even if the other
cross was fertile: and just as characters now co-ordinated may have been
separately accumulated by Natural Selection, so the reciprocal crosses may
have become sterile one at a time.


LETTER 212. TO A.R. WALLACE.
4, Chester Place, March 17th, 1868.

(212/1. Mr. Darwin had already written a short note to Mr. Wallace
expressing a general dissent from his view.)

I do not feel that I shall grapple with the sterility argument till my
return home; I have tried once or twice, and it has made my stomach feel as
if it had been placed in a vice. Your paper has driven three of my
children half mad--one sat up till 12 o'clock over it. My second son, the
mathematician, thinks that you have omitted one almost inevitable deduction
which apparently would modify the result. He has written out what he
thinks, but I have not tried fully to understand him. I suppose that you
do not care enough about the subject to like to see what he has written.


LETTER 212A. A.R. WALLACE TO CHARLES DARWIN.
Hurstpierpoint, March, 24th [1868].

I return your son's notes with my notes on them. Without going into any
details, is not this a strong general argument?

1. A species varies occasionally in two directions, but owing to their
free intercrossing the varieties never increase.

2. A change of conditions occurs which threatens the existence of the
species; but the two varieties are adapted to the changing conditions, and
if accumulated will form two new species adapted to the new conditions.

3. Free crossing, however, renders this impossible, and so the species is
in danger of extinction.

4. If sterility would be induced, then the pure races would increase more
rapidly, and replace the old species.

5. It is admitted that partial sterility between varieties does
occasionally occur. It is admitted [that] the degree of this sterility
varies; is it not probable that Natural Selection can accumulate these
variations, and thus save the species? If Natural Selection can NOT do
this, how do species ever arise, except when a variety is isolated?

Closely allied species in distinct countries being sterile is no
difficulty; for either they diverged from a common ancestor in contact, and
Natural Selection increased the sterility, or they were isolated, and have
varied since: in which case they have been for ages influenced by distinct
conditions which may well produce sterility.

If the difficulty of grafting was as great as the difficulty of crossing,
and as regular, I admit it would be a most serious objection. But it is
not. I believe many distinct species can be grafted, while others less
distinct cannot. The regularity with which natural species are sterile
together, even when very much alike, I think is an argument in favour of
the sterility having been generally produced by Natural Selection for the
good of the species.

The other difficulty, of unequal sterility of reciprocal crosses, seems
none to me; for it is a step to more complete sterility, and as such would
be increased by selection.


LETTER 213. TO A.R. WALLACE.
Down, April 6th [1868].

I have been considering the terrible problem. Let me first say that no man
could have more earnestly wished for the success of Natural Selection in
regard to sterility than I did; and when I considered a general statement
(as in your last note) I always felt sure it could be worked out, but
always failed in detail. The cause being, as I believe, that Natural
Selection cannot effect what is not good for the individual, including in
this term a social community. It would take a volume to discuss all the
points, and nothing is so humiliating to me as to agree with a man like you
(or Hooker) on the premises and disagree about the result.

I agree with my son's argument and not with the rejoinder. The cause of
our difference, I think, is that I look at the number of offspring as an
important element (all circumstances remaining the same) in keeping up the
average number of individuals within any area. I do not believe that the
amount of food by any means is the sole determining cause of number.
Lessened fertility is equivalent to a new source of destruction. I believe
if in one district a species produced from any cause fewer young, the
deficiency would be supplied from surrounding districts. This applies to
your Paragraph 5. (213/1. See Letter 211.) If the species produced fewer
young from any cause in every district, it would become extinct unless its
fertility were augmented through Natural Selection (see H. Spencer).

I demur to probability and almost to possibility of Paragraph 1., as you
start with two forms within the same area, which are not mutually sterile,
and which yet have supplanted the parent-form.

(Paragraph 6.) I know of no ghost of a fact supporting belief that
disinclination to cross accompanies sterility. It cannot hold with plants,
or the lower fixed aquatic animals. I saw clearly what an immense aid this
would be, but gave it up. Disinclination to cross seems to have been
independently acquired, probably by Natural Selection; and I do not see why
it would not have sufficed to have prevented incipient species from
blending to have simply increased sexual disinclination to cross.

(Paragraph 11.) I demur to a certain extent to amount of sterility and
structural dissimilarity necessarily going together, except indirectly and
by no means strictly. Look at vars. of pigeons, fowls, and cabbages.

I overlooked the advantage of the half-sterility of reciprocal crosses;
yet, perhaps from novelty, I do not feel inclined to admit probability of
Natural Selection having done its work so queerly.

I will not discuss the second case of utter sterility, but your assumptions
in Paragraph 13 seem to me much too complicated. I cannot believe so
universal an attribute as utter sterility between remote species was
acquired in so complex a manner. I do not agree with your rejoinder on
grafting: I fully admit that it is not so closely restricted as crossing,
but this does not seem to me to weaken the case as one of analogy. The
incapacity of grafting is likewise an invariable attribute of plants
sufficiently remote from each other, and sometimes of plants pretty closely
allied.

The difficulty of increasing the sterility through Natural Selection of two
already sterile species seems to me best brought home by considering an
actual case. The cowslip and primrose are moderately sterile, yet
occasionally produce hybrids. Now these hybrids, two or three or a dozen
in a whole parish, occupy ground which might have been occupied by either
pure species, and no doubt the latter suffer to this small extent. But can
you conceive that any individual plants of the primrose and cowslip which
happened to be mutually rather more sterile (i.e. which, when crossed,
yielded a few less seed) than usual, would profit to such a degree as to
increase in number to the ultimate exclusion of the present primrose and
cowslip? I cannot.

My son, I am sorry to say, cannot see the full force of your rejoinder in
regard to second head of continually augmented sterility. You speak in
this rejoinder, and in Paragraph 5, of all the individuals becoming in some
slight degree sterile in certain districts: if you were to admit that by
continued exposure to these same conditions the sterility would inevitably
increase, there would be no need of Natural Selection. But I suspect that
the sterility is not caused so much by any particular conditions as by long
habituation to conditions of any kind. To speak according to pangenesis,
the gemmules of hybrids are not injured, for hybrids propagate freely by
buds; but their reproductive organs are somehow affected, so that they
cannot accumulate the proper gemmules, in nearly the same manner as the
reproductive organs of a pure species become affected when exposed to
unnatural conditions.

This is a very ill-expressed and ill-written letter. Do not answer it,
unless the spirit urges you. Life is too short for so long a discussion.
We shall, I greatly fear, never agree.


LETTER 214. A.R. WALLACE TO CHARLES DARWIN.
Hurstpierpoint, [April?] 8th, 1868.

I am sorry you should have given yourself the trouble to answer my ideas on
sterility. If you are not convinced, I have little doubt but that I am
wrong; and, in fact, I was only half convinced by my own arguments, and I
now think there is about an even chance that Natural Selection may or may
not be able to accumulate sterility. If my first proposition is modified
to the existence of a species and a variety in the same area, it will do
just as well for my argument. Such certainly do exist. They are fertile
together, and yet each maintains itself tolerably distinct. How can this
be, if there is no disinclination to crossing?

My belief certainly is that number of offspring is not so important an
element in keeping up population of a species as supply of food and other
favourable conditions; because the numbers of a species constantly vary
greatly in different parts of its own area, whereas the average number of
offspring is not a very variable element.

However, I will say no more, but leave the problem as insoluble, only
fearing that it will become a formidable weapon in the hands of the enemies
of Natural Selection.


LETTER 215. TO J.D. HOOKER.

(215/1. The following extract from a letter to Sir Joseph Hooker (dated
April 3rd, 1868) refers to his Presidential Address for the approaching
meeting of the British Association at Norwich.

Some account of Sir Joseph's success is given in the "Life and Letters,"
III., page 100, also in Huxley's "Life," Volume I., page 297, where Huxley
writes to Darwin:--

"We had a capital meeting at Norwich, and dear old Hooker came out in great
force, as he always does in emergencies. The only fault was the terrible
'Darwinismus' which spread over the section and crept out when you least
expected it, even in Fergusson's lecture on 'Buddhist Temples.' You will
have the rare happiness to see your ideas triumphant during your lifetime.

"P.S.--I am going into opposition; I can't stand it.")

Down, April 3rd [1868].

I have been thinking over your Presidential Address; I declare I made
myself quite uncomfortable by fancying I had to do it, and feeling myself
utterly dumbfounded.

But I do not believe that you will find it so difficult. When you come to
Down I shall be very curious to hear what your ideas are on the subject.

Could you make anything out of a history of the great steps in the progress
of Botany, as representing the whole of Natural History? Heaven protect
you! I suppose there are men to whom such a job would not be so awful as
it appears to me...If you had time, you ought to read an article by W.
Bagehot in the April number of the "Fortnightly" (215/2. "Physic and
Politics," "Fortnightly Review," Volume III., page 452, 1868.), applying
Natural Selection to early or prehistoric politics, and, indeed, to late
politics,--this you know is your view.


LETTER 216. A.R. WALLACE TO CHARLES DARWIN.
9, St. Mark's Crescent, N.W., August 16th [1868].

I ought to have written before to thank you for the copies of your papers
on Primula and on "Cross-unions of Dimorphic Plants, etc." The latter is
particularly interesting and the conclusion most important; but I think it
makes the difficulty of how these forms, with their varying degrees of
sterility, originated, greater than ever. If "natural selection" could not
accumulate varying degrees of sterility for the plant's benefit, then how
did sterility ever come to be associated with one cross of a trimorphic
plant rather than another? The difficulty seems to be increased by the
consideration that the advantage of a cross with a distinct individual is
gained just as well by illegitimate as by legitimate unions. By what
means, then, did illegitimate unions ever become sterile? It would seem a
far simpler way for each plant's pollen to have acquired a prepotency on
another individual's stigma over that of the same individual, without the
extraordinary complication of three differences of structure and eighteen
different unions with varying degrees of sterility!

However, the fact remains an excellent answer to the statement that
sterility of hybrids proves the absolute distinctness of the parents.

I have been reading with great pleasure Mr. Bentham's last admirable
address (216/1. "Proc. Linn. Soc." 1867-8, page lvii.), in which he so
well replies to the gross misstatements of the "Athenaeum;" and also says
award in favour of pangenesis. I think we may now congratulate you on
having made a valuable convert, whose opinions on the subject, coming so
late and being evidently so well considered, will have much weight.

I am going to Norwich on Tuesday to hear Dr. Hooker, who I hope will boldly
promulgate "Darwinism" in his address. (216/2. Sir Joseph Hooker's
Presidential Address at the British Association Meeting.) Shall we have
the pleasure of seeing you there?

I am engaged in negociations about my book.

Hoping you are well and getting on with your next volumes.

(216/3. We are permitted by Mr. Wallace to append the following note as to
his more recent views on the question of Natural Selection and sterility:--

"When writing my "Darwinism," and coming again to the consideration of this
problem of the effect of Natural Selection in accumulating variations in
the amount of sterility between varieties or incipient species twenty years
later, I became more convinced, than I was when discussing with Darwin, of
the substantial accuracy of my argument. Recently a correspondent who is
both a naturalist and a mathematician has pointed out to me a slight error
in my calculation at page 183 (which does not, however, materially affect
the result), disproving the 'physiological selection' of the late Dr.
Romanes, but he can see no fallacy in my argument as to the power of
Natural Selection to increase sterility between incipient species, nor, so
far as I am aware, has any one shown such fallacy to exist.

"On the other points on which I differed from Mr. Darwin in the foregoing
discussion--the effect of high fertility on population of a species, etc.--
I still hold the views I then expressed, but it would be out of place to
attempt to justify them here."

A.R.W. (1899).)


LETTER 217. TO C. LYELL.
Down, October 4th [1867].

With respect to the points in your note, I may sometimes have expressed
myself with ambiguity. At the end of Chapter XXIII., where I say that
marked races are not often (you omit "often") produced by changed
conditions (217/1. "Hence, although it must be admitted that new
conditions of life do sometimes definitely affect organic beings, it may be
doubted whether well-marked races have often been produced by the direct
action of changed conditions without the aid of selection either by man or
nature." ("Animals and Plants," Volume II., page 292, 1868.)), I intended
to refer to the direct action of such conditions in causing variation, and
not as leading to the preservation or destruction of certain forms. There
is as wide a difference in these two respects as between voluntary
selection by man and the causes which induce variability. I have somewhere
in my book referred to the close connection between Natural Selection and
the action of external conditions in the sense which you specify in your
note. And in this sense all Natural Selection may be said to depend on
changed conditions. In the "Origin" I think I have underrated (and from
the cause which you mention) the effects of the direct action of external
conditions in producing varieties; but I hope in Chapter XXIII. I have
struck as fair a balance as our knowledge permits.

It is wonderful to me that you have patience to read my slips, and I cannot
but regret, as they are so imperfect; they must, I think, give you a wrong
impression, and had I sternly refused, you would perhaps have thought
better of my book. Every single slip is greatly altered, and I hope
improved.

With respect to the human ovule, I cannot find dimensions given, though I
have often seen the statement. My impression is that it would be just or
barely visible if placed on a clear piece of glass. Huxley could answer
your question at once.

I have not been well of late, and have made slow progress, but I think my
book will be finished by the middle of November.


LETTER 218. A.R. WALLACE TO CHARLES DARWIN.
[End of February, 1868]

I am in the second volume of your book, and I have been astonished at the
immense number of interesting facts you have brought together. I read the
chapter on pangenesis first, for I could not wait. I can hardly tell you
how much I admire it. It is a positive comfort to me to have any feasible
explanation of a difficulty that has always been haunting me, and I shall
never be able to give it up till a better one supplies its place,--and that
I think hardly possible. You have now fairly beaten Spencer on his own
ground, for he really offered no solution of the difficulties of the
problem. The incomprehensible minuteness and vast numbers of the
physiological germs or atoms (which themselves must be compounded of
numbers of Spencer's physiological units) is the only difficulty; but that
is only on a par with the difficulties in all conceptions of matter, space,
motion, force, etc.

As I understood Spencer, his physiological units were identical throughout
each species, but slightly different in each different species; but no
attempt was made to show how the identical form of the parent or ancestors
came to be built up of such units.


LETTER 219. TO A.R. WALLACE.
Down, February 27th [1868].

You cannot well imagine how much I have been pleased by what you say about
pangenesis. None of my friends will speak out, except to a certain extent
Sir H. Holland, who found it very tough reading, but admits that some view
"closely akin to it" will have to be admitted. Hooker, as far as I
understand him, which I hardly do at present, seems to think that the
hypothesis is little more than saying that organisms have such and such
potentialities. What you say exactly and fully expresses my feelings--
viz., that it is a relief to have some feasible explanation of the various
facts, which can be given up as soon as any better hypothesis is found. It
has certainly been an immense relief to my mind; for I have been stumbling
over the subject for years, dimly seeing that some relation existed between
the various classes of facts. I now hear from H. Spencer that his views
quoted in my footnote refer to something quite distinct, as you seem to
have perceived. (219/1. This letter is published in "Life and Letters,"
III., page 79.)


LETTER 220. A.R. WALLACE TO CHARLES DARWIN.
Hurstpierpoint, March 1st, 1868.

...Sir C. Lyell spoke to me as if he has greatly admired pangenesis. I am
very glad H. Spencer at once acknowledges that his view was something quite
distinct from yours. Although, as you know, I am a great admirer of his, I
feel how completely his view failed to go to the root of the matter, as
yours does. His explained nothing, though he was evidently struggling hard
to find an explanation. Yours, as far as I can see, explains everything in
growth and reproduction--though, of course, the mystery of life and
consciousness remains as great as ever.

Parts of the chapter on pangenesis I found hard reading, and have not quite
mastered yet, and there are also throughout the discussions in Volume II.
many bits of hard reading, on minute points which we, who have not worked
experimentally at cultivation and crossing, as you have done, can hardly
see the importance of, or their bearing on the general question.

If I am asked, I may perhaps write an article on the book for some
periodical, and, if so, shall do what I can to make "Pangenesis"
appreciated...

(220/1. In "Nature," May 25th, 1871, page 69, appeared a letter on
pangenesis from Mr. A.C. Ranyard, dealing with the difficulty that the
"sexual elements produced upon the scion" have not been shown to be
affected by the stock. Mr. Darwin, in an annotated copy of this letter,
disputes the accuracy of the statement, but adds: "THE BEST OBJECTION YET
RAISED." He seems not to have used Mr. Ranyard's remarks in the 2nd
edition of the "Variation of Animals and Plants," 1875.)


LETTER 221. TO J.D. HOOKER.
Down, May 21st [1868].

I know that you have been overworking yourself, and that makes you think
that you are doing nothing in science. If this is the case (which I do not
believe), your intellect has all run to letter-writing, for I never in all
my life received a pleasanter one than your last. It greatly amused us
all. How dreadfully severe you are on the Duke (221/1. The late Duke of
Argyll, whose "Reign of Law" Sir J.D. Hooker had been reading.): I really
think too severe, but then I am no fair judge, for a Duke, in my eyes, is
no common mortal, and not to be judged by common rules! I pity you from
the bottom of my soul about the address (221/2. Sir Joseph was President
of the British Association at Norwich in 1868: see "Life and Letters,"
III., page 100. The reference to "Insular Floras" is to Sir Joseph's
lecture at the Nottingham meeting of the British Association in 1866: see
"Life and Letters," III., page 47.): it makes my flesh creep; but when I
pitied you to Huxley, he would not join at all, and would only say that you
did and delivered your Insular Flora lecture so admirably in every way that
he would not bestow any pity on you. He felt certain that you would keep
your head high up. Nevertheless, I wish to God it was all over for your
sake. I think, from several long talks, that Huxley will give an excellent
and original lecture on Geograph. Distrib. of birds. I have been working
very hard--too hard of late--on Sexual Selection, which turns out a
gigantic subject; and almost every day new subjects turn up requiring
investigation and leading to endless letters and searches through books. I
am bothered, also, with heaps of foolish letters on all sorts of subjects,
but I am much interested in my subject, and sometimes see gleams of light.
All my other letters have prevented me indulging myself in writing to you;
but I suddenly found the locust grass (221/3. No doubt the plants raised
from seeds taken from locust dung sent by Mr. Weale from South Africa. The
case is mentioned in the fifth edition of the "Origin," published in 1869,
page 439.) yesterday in flower, and had to despatch it at once. I suppose
some of your assistants will be able to make the genus out without great
trouble. I have done little in experiment of late, but I find that
mignonette is absolutely sterile with pollen from the same plant. Any one
who saw stamen after stamen bending upwards and shedding pollen over the
stigmas of the same flower would declare that the structure was an
admirable contrivance for self-fertilisation. How utterly mysterious it is
that there should be some difference in ovules and contents of pollen-
grains (for the tubes penetrate own stigma) causing fertilisation when
these are taken from any two distinct plants, and invariably leading to
impotence when taken from the same plant! By Jove, even Pan. (221/4.
Pangenesis.) won't explain this. It is a comfort to me to think that you
will be surely haunted on your death-bed for not honouring the great god
Pan. I am quite delighted at what you say about my book, and about
Bentham; when writing it, I was much interested in some parts, but latterly
I thought quite as poorly of it as even the "Athenaeum." It ought to be
read abroad for the sake of the booksellers, for five editions have come or
are coming out abroad! I am ashamed to say that I have read only the
organic part of Lyell, and I admire all that I have read as much as you.
It is a comfort to know that possibly when one is seventy years old one's
brain may be good for work. It drives me mad, and I know it does you too,
that one has no time for reading anything beyond what must be read: my
room is encumbered with unread books. I agree about Wallace's wonderful
cleverness, but he is not cautious enough in my opinion. I find I must
(and I always distrust myself when I differ from him) separate rather
widely from him all about birds' nests and protection; he is riding that
hobby to death. I never read anything so miserable as Andrew Murray's
criticism on Wallace in the last number of his Journal. (221/5. See
"Journal of Travel and Natural History," Volume I., No. 3, page 137,
London, 1868, for Andrew Murray's "Reply to Mr. Wallace's Theory of Birds'
Nests," which appeared in the same volume, page 73. The "Journal" came to
an end after the publication of one volume for 1867-8.) I believe this
Journal will die, and I shall not cry: what a contrast with the old
"Natural History Review."

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