More Letters of Charles Darwin Volume II

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(PLATE: MR. A.R. WALLACE, 1878. From a photograph by Maull & Fox.)

LETTER 389. TO A.R. WALLACE.

(389/1. Published in "Life and Letters," III., page 230.)

(389/2. The following five letters refer to Mr. Wallace's "Geographical
Distribution of Animals," 1876.)

[Hopedene] (389/3. Mr. Hensleigh Wedgwood's house in Surrey.), June 5th,
1876.

I must have the pleasure of expressing to you my unbounded admiration of
your book (389/4. "Geographical Distribution," 1876.), though I have read
only to page 184--my object having been to do as little as possible while
resting. I feel sure that you have laid a broad and safe foundation for
all future work on Distribution. How interesting it will be to see
hereafter plants treated in strict relation to your views; and then all
insects, pulmonate molluscs and fresh-water fishes, in greater detail than
I suppose you have given to these lower animals. The point which has
interested me most, but I do not say the most valuable point, is your
protest against sinking imaginary continents in a quite reckless manner, as
was stated by Forbes, followed, alas, by Hooker, and caricatured by
Wollaston and [Andrew] Murray! By the way, the main impression that the
latter author has left on my mind is his utter want of all scientific
judgment. I have lifted up my voice against the above view with no avail,
but I have no doubt that you will succeed, owing to your new arguments and
the coloured chart. Of a special value, as it seems to me, is the
conclusion that we must determine the areas, chiefly by the nature of the
mammals. When I worked many years ago on this subject, I doubted much
whether the now-called Palaearctic and Nearctic regions ought to be
separated; and I determined if I made another region that it should be
Madagascar. I have, therefore, been able to appreciate your evidence on
these points. What progress Palaeontology has made during the last twenty
years! but if it advances at the same rate in the future, our views on the
migration and birthplace of the various groups will, I fear, be greatly
altered. I cannot feel quite easy about the Glacial period, and the
extinction of large mammals, but I must hope that you are right. I think
you will have to modify your belief about the difficulty of dispersal of
land molluscs; I was interrupted when beginning to experimentise on the
just hatched young adhering to the feet of ground-roosting birds. I differ
on one other point--viz. in the belief that there must have existed a
Tertiary Antarctic continent, from which various forms radiated to the
southern extremities of our present continents. But I could go on
scribbling forever. You have written, as I believe, a grand and memorable
work, which will last for years as the foundation for all future treatises
on Geographical Distribution.

P.S.--You have paid me the highest conceivable compliment, by what you say
of your work in relation to my chapters on distribution in the "Origin,"
and I heartily thank you for it.

LETTER 390. FROM A.R. WALLACE TO CHARLES DARWIN.
The Dell, Grays, Essex, June 7th, 1876.

Many thanks for your very kind letter. So few people will read my book at
all regularly, that a criticism from one who does so will be very welcome.
If, as I suppose, it is only to page 184 of Volume I. that you have read,
you cannot yet quite see my conclusions on the points you refer to (land
molluscs and Antarctic continent). My own conclusion fluctuated during the
progress of the book, and I have, I know, occasionally used expressions
(the relics of earlier ideas) which are not quite consistent with what I
say further on. I am positively against any Southern continent as uniting
South America with Australia or New Zealand, as you will see at Volume I.,
pages 398-403, and 459-66. My general conclusions as to distribution of
land mollusca are at Volume II., pages 522-9. (390/1. "Geographical
Distribution" II., pages 524, 525. Mr. Wallace points out that "hardly a
small island on the globe but has some land-shells peculiar to it"--and he
goes so far as to say that probably air-breathing mollusca have been
chiefly distributed by air- or water-carriage, rather than by voluntary
dispersal on the land.) When you have read these passages, and looked at
the general facts which lead to them, I shall be glad to hear if you still
differ from me.

Though, of course, present results as to the origin and migrations of
genera of mammals will have to be modified owing to new discoveries, I
cannot help thinking that much will remain unaffected, because in all
geographical and geological discoveries the great outlines are soon
reached, the details alone remain to be modified. I also think much of the
geological evidence is now so accordant with, and explanatory of,
Geographical Distribution, that it is prima facie correct in outline.
Nevertheless, such vast masses of new facts will come out in the next few
years that I quite dread the labour of incorporating them in a new edition.

I hope your health is improved; and when, quite at your leisure, you have
waded through my book, I trust you will again let me have a few lines of
friendly criticism and advice.

LETTER 391. TO A.R. WALLACE.
Down, June 17th, 1876.

I have now finished the whole of Volume I., with the same interest and
admiration as before; and I am convinced that my judgment was right and
that it is a memorable book, the basis of all future work on the subject.
I have nothing particular to say, but perhaps you would like to hear my
impressions on two or three points. Nothing has struck me more than the
admirable and convincing manner in which you treat Java. To allude to a
very trifling point, it is capital about the unadorned head of the Argus-
pheasant. (391/1. See "Descent of Man," Edition I., pages 90 and 143, for
drawings of the Argus pheasant and its markings. The ocelli on the wing
feathers were favourite objects of Mr. Darwin, and sometimes formed the
subject of the little lectures which on rare occasions he would give to a
visitor interested in Natural History. In Mr. Wallace's book the meaning
of the ocelli comes in by the way, in the explanation of Plate IX., "A
Malayan Forest with some of its peculiar Birds." Mr. Wallace (volume i.,
page 340) points out that the head of the Argus pheasant is, during the
display of the wings, concealed from the view of a spectator in front, and
this accounts for the absence of bright colour on the head--a most unusual
point in a pheasant. The case is described as a "remarkable confirmation
of Mr. Darwin's views, that gaily coloured plumes are developed in the male
bird for the purpose of attractive display." For the difference of opinion
between the two naturalists on the broad question of coloration see "Life
and Letters," III., page 123. See Letters 440-453.) How plain a thing is,
when it is once pointed out! What a wonderful case is that of Celebes: I
am glad that you have slightly modified your views with respect to Africa.
(391/2. "I think this must refer to the following passage in 'Geog. Dist.
of Animals,' Volume I., pages 286-7. 'At this period (Miocene) Madagascar
was no doubt united with Africa, and helped to form a great southern
continent which must at one time have extended eastward as far as Southern
India and Ceylon; and over the whole of this the lemurine type no doubt
prevailed.' At the time this was written I had not paid so much attention
to islands, and in my "Island Life" I have given ample reasons for my
belief that the evidence of extinct animals does not require any direct
connection between Southern India and Africa."--Note by Mr. Wallace.) And
this leads me to say that I cannot swallow the so-called continent of
Lemuria--i.e., the direct connection of Africa and Ceylon. (391/3. See
"Geographical Distribution," I., page 76. The name Lemuria was proposed by
Mr. Sclater for an imaginary submerged continent extending from Madagascar
to Ceylon and Sumatra. Mr. Wallace points out that if we confine ourselves
to facts Lemuria is reduced to Madagascar, which he makes a subdivision of
the Ethiopian Region.) The facts do not seem to me many and strong enough
to justify so immense a change of level. Moreover, Mauritius and the other
islands appear to me oceanic in character. But do not suppose that I place
my judgment on this subject on a level with yours. A wonderfully good
paper was published about a year ago on India, in the "Geological Journal,"
I think by Blanford. (391/4. H.F. Blanford "On the Age and Correlations
of the Plant-bearing Series of India and the Former Existence of an Indo-
Oceanic Continent" ("Quart. Journ. Geol. Soc." XXXI., 1875, page 519). The
name Gondwana-Land was subsequently suggested by Professor Suess for this
Indo-Oceanic continent. Since the publication of Blanford's paper, much
literature has appeared dealing with the evidence furnished by fossil
plants, etc., in favour of the existence of a vast southern continent.)
Ramsay agreed with me that it was one of the best published for a long
time. The author shows that India has been a continent with enormous
fresh-water lakes, from the Permian period to the present day. If I
remember right, he believes in a former connection with S. Africa.

I am sure that I read, some twenty to thirty years ago in a French journal,
an account of teeth of Mastodon found in Timor; but the statement may have
been an error. (391/5. In a letter to Falconer (Letter 155), January 5th,
1863, Darwin refers to the supposed occurrence of Mastodon as having been
"smashed" by Falconer.)

With respect to what you say about the colonising of New Zealand, I
somewhere have an account of a frog frozen in the ice of a Swiss glacier,
and which revived when thawed. I may add that there is an Indian toad
which can resist salt-water and haunts the seaside. Nothing ever
astonished me more than the case of the Galaxias; but it does not seem
known whether it may not be a migratory fish like the salmon. (391/6. The
only genus of the Galaxidae, a family of fresh-water fishes occurring in
New Zealand, Tasmania, and Tierra del Fuego, ranging north as far as
Queensland and Chile (Wallace's "Geographical Distribution," II., page
448).)

LETTER 392. TO A.R. WALLACE.
Down, June 25th, 1876.

I have been able to read rather more quickly of late, and have finished
your book. I have not much to say. Your careful account of the temperate
parts of South America interested me much, and all the more from knowing
something of the country. I like also much the general remarks towards the
end of the volume on the land molluscs. Now for a few criticisms.

Page 122. (392/1. The pages refer to Volume II. of Wallace's
"Geographical Distribution.")--I am surprised at your saying that "during
the whole Tertiary period North America was zoologically far more strongly
contrasted with South America than it is now." But we know hardly anything
of the latter except during the Pliocene period; and then the mastodon,
horse, several great edentata, etc., etc., were common to the north and
south. If you are right, I erred greatly in my "Journal," where I insisted
on the former close connection between the two.

Page 252 and elsewhere.--I agree thoroughly with the general principle that
a great area with many competing forms is necessary for much and high
development; but do you not extend this principle too far--I should say
much too far, considering how often several species of the same genus have
been developed on very small islands?

Page 265.--You say that the Sittidae extend to Madagascar, but there is no
number in the tabular heading. [The number (4) was erroneously omitted.--
A.R.W.]

Page 359.--Rhinochetus is entered in the tabular heading under No. 3 of the
neotropical subregions. [An error: should have been the Australian.--
A.R.W.]

Reviewers think it necessary to find some fault; and if I were to review
you, the sole point which I should blame is your not giving very numerous
references. These would save whoever follows you great labour.
Occasionally I wished myself to know the authority for certain statements,
and whether you or somebody else had originated certain subordinate views.
Take the case of a man who had collected largely on some island, for
instance St. Helena, and who wished to work out the geographical relations
of his collections: he would, I think, feel very blank at not finding in
your work precise references to all that had been written on St. Helena. I
hope you will not think me a confoundedly disagreeable fellow.

I may mention a capital essay which I received a few months ago from Axel
Blytt (392/2. Axel Blytt, "Essay on the Immigration of the Norwegian
Flora." Christiania, 1876. See Letter 387.) on the distribution of the
plants of Scandinavia; showing the high probability of there having been
secular periods alternately wet and dry, and of the important part which
they have played in distribution.

I wrote to Forel (392/3. See Letter 388.), who is always at work on ants,
and told him your views about the dispersal of the blind coleoptera, and
asked him to observe.

I spoke to Hooker about your book, and feel sure that he would like nothing
better than to consider the distribution of plants in relation to your
views; but he seemed to doubt whether he should ever have time.

And now I have done my jottings, and once again congratulate you on having
brought out so grand a work. I have been a little disappointed at the
review in "Nature." (392/4. June 22nd, 1876, pages 165 et seq.)

LETTER 393. A.R. WALLACE TO CHARLES DARWIN.
Rosehill, Dorking, July 23rd, 1876.

I should have replied sooner to your last kind and interesting letters, but
they reached me in the midst of my packing previous to removal here, and I
have only just now got my books and papers in a get-at-able state.

And first, many thanks for your close observation in detecting the two
absurd mistakes in the tabular headings.

As to the former greater distinction of the North and South American
faunas, I think I am right. The edentata being proved (as I hold) to have
been mere temporary migrants into North America in the post-Pliocene epoch,
form no part of its Tertiary fauna. Yet in South America they were so
enormously developed in the Pliocene epoch that we know, if there is any
such thing as evolution, etc., that strange ancestral forms must have
preceded them in Miocene times.

Mastodon, on the other hand, represented by one or two species only,
appears to have been a late immigrant into South America from the north.

The immense development of ungulates (in varied families, genera, and
species) in North America during the whole Tertiary epoch is, however, the
great feature which assimilates it to Europe, and contrasts it with South
America. True camels, hosts of hog-like animals, true rhinoceroses, and
hosts of ancestral horses, all bring the North American [fauna] much nearer
to the Old World than it is now. Even the horse, represented in all South
America by Equus only, was probably a temporary immigrant from the north.

As to extending too far the principle (yours) of the necessity of
comparatively large areas for the development of varied faunas, I may have
done so, but I think not. There is, I think, every probability that most
islands, etc., where a varied fauna now exists, have been once more
extensive--eg., New Zealand, Madagascar: where there is no such evidence
(e.g., Galapagos), the fauna is very restricted.

Lastly, as to want of references: I confess the justice of your criticism;
but I am dreadfully unsystematic. It is my first large work involving much
of the labour of others. I began with the intention of writing a
comparatively short sketch, enlarged it, and added to it bit by bit;
remodelled the tables, the headings, and almost everything else, more than
once, and got my materials in such confusion that it is a wonder it has not
turned out far more crooked and confused than it is. I, no doubt, ought to
have given references; but in many cases I found the information so small
and scattered, and so much had to be combined and condensed from
conflicting authorities, that I hardly knew how to refer to them or where
to leave off. Had I referred to all authors consulted for every fact, I
should have greatly increased the bulk of the book, while a large portion
of the references would be valueless in a few years, owing to later and
better authorities. My experience of referring to references has generally
been most unsatisfactory. One finds, nine times out of ten, the fact is
stated, and nothing more; or a reference to some third work not at hand!

I wish I could get into the habit of giving chapter and verse for every
fact and extract; but I am too lazy, and generally in a hurry, having to
consult books against time, when in London for a day.

However, I will try to do something to mend this matter, should I have to
prepare another edition.

I return you Forel's letter. It does not advance the question much;
neither do I think it likely that even the complete observation he thinks
necessary would be of much use, because it may well be that the ova, or
larvae, or imagos of the beetles are not carried systematically by the
ants, but only occasionally, owing to some exceptional circumstances. This
might produce a great effect in distribution, yet be so rare as never to
come under observation.

Several of your remarks in previous letters I shall carefully consider. I
know that, compared with the extent of the subject, my book is in many
parts crude and ill-considered; but I thought, and still think, it better
to make some generalisations wherever possible, as I am not at all afraid
of having to alter my views in many points of detail. I was so overwhelmed
with zoological details, that I never went through the Geological Society's
"Journal" as I ought to have done, and as I mean to do before writing more
on the subject.

LETTER 394. TO F. BUCHANAN WHITE.

(394/1. "Written in acknowledgment of a copy of a paper (published by me
in the "Proceedings of the Zoological Society") on the Hemiptera of St.
Helena, but discussing the origin of the whole fauna and flora of that
island."--F.B.W.)

Down, September 23rd. [1878].

I have now read your paper, and I hope that you will not think me
presumptuous in writing another line to say how excellent it seems to me.
I believe that you have largely solved the problem of the affinities of the
inhabitants of this most interesting little island, and this is a
delightful triumph.

LETTER 395. TO J.D. HOOKER.
Down, July 22nd [1879].

I have just read Ball's Essay. (395/1. The late John Ball's lecture "On
the Origin of the Flora of the Alps" in the "Proceedings of the R. Geogr.
Soc." 1879. Ball argues (page 18) that "during ancient Palaeozoic times,
before the deposition of the Coal-measures, the atmosphere contained twenty
times as much carbonic acid gas and considerably less oxygen than it does
at present." He further assumes that in such an atmosphere the percentage
of CO2 in the higher mountains would be excessively different from that at
the sea-level, and appends the result of calculations which gives the
amount of CO2 at the sea-level as 100 per 10,000 by weight, at a height of
10,000 feet as 12.5 per 10,000. Darwin understands him to mean that the
Vascular Cryptogams and Gymnosperms could stand the sea-level atmosphere,
whereas the Angiosperms would only be able to exist in the higher regions
where the percentage of CO2 was small. It is not clear to us that Ball
relies so largely on the condition of the atmosphere as regards CO2. If he
does he is clearly in error, for everything we know of assimilation points
to the conclusion that 100 per 10,000 (1 per cent.) is by no means a
hurtful amount of CO2, and that it would lead to an especially vigorous
assimilation. Mountain plants would be more likely to descend to the
plains to share in the rich feast than ascend to higher regions to avoid
it. Ball draws attention to the imperfection of our plant records as
regards the floras of mountain regions. It is, he thinks, conceivable that
there existed a vegetation on the Carboniferous mountains of which no
traces have been preserved in the rocks. See "Fossil Plants as Tests of
Climate," page 40, A.C. Seward, 1892.

Since the first part of this note was written, a paper has been read (May
29th, 1902) by Dr. H.T. Brown and Mr. F. Escombe, before the Royal Society
on "The Influence of varying amounts of Carbon Dioxide in the Air on the
Photosynthetic Process of Leaves, and on the Mode of Growth of Plants."
The author's experiments included the cultivation of several dicotyledonous
plants in an atmosphere containing in one case 180 to 200 times the normal
amount of CO2, and in another between three and four times the normal
amount. The general results were practically identical in the two sets of
experiments. "All the species of flowering plants, which have been the
subject of experiment, appear to be accurately 'tuned' to an atmospheric
environment of three parts of CO2 per 10,000, and the response which they
make to slight increases in this amount are in a direction altogether
unfavourable to their growth and reproduction." The assimilation of carbon
increases with the increase in the partial pressure of the CO2. But there
seems to be a disturbance in metabolism, and the plants fail to take
advantage of the increased supply of CO2. The authors say:--"All we are
justified in concluding is, that if such atmospheric variations have
occurred since the advent of flowering plants, they must have taken place
so slowly as never to outrun the possible adaptation of the plants to their
changing conditions."

Prof. Farmer and Mr. S.E. Chandler gave an account, at the same meeting of
the Royal Society, of their work "On the Influence of an Excess of Carbon
Dioxide in the Air on the Form and Internal Structure of Plants." The
results obtained were described as differing in a remarkable way from those
previously recorded by Teodoresco ("Rev. Gen. Botanique," II., 1899

It is hoped that Dr. Horace Brown and Mr. Escombe will extend their
experiments to Vascular Cryptogams, and thus obtain evidence bearing more
directly upon the question of an increased amount of CO2 in the atmosphere
of the Coal-period forests.) It is pretty bold. The rapid development as
far as we can judge of all the higher plants within recent geological times
is an abominable mystery. Certainly it would be a great step if we could
believe that the higher plants at first could live only at a high level;
but until it is experimentally [proved] that Cycadeae, ferns, etc., can
withstand much more carbonic acid than the higher plants, the hypothesis
seems to me far too rash. Saporta believes that there was an astonishingly
rapid development of the high plants, as soon [as] flower-frequenting
insects were developed and favoured intercrossing. I should like to see
this whole problem solved. I have fancied that perhaps there was during
long ages a small isolated continent in the S. Hemisphere which served as
the birthplace of the higher plants--but this is a wretchedly poor
conjecture. It is odd that Ball does not allude to the obvious fact that
there must have been alpine plants before the Glacial period, many of which
would have returned to the mountains after the Glacial period, when the
climate again became warm. I always accounted to myself in this manner for
the gentians, etc.

Ball ought also to have considered the alpine insects common to the Arctic
regions. I do not know how it may be with you, but my faith in the glacial
migration is not at all shaken.

LETTER 396. A.R. WALLACE TO CHARLES DARWIN.

(396/1. This letter is in reply to Mr. Darwin's criticisms on Mr.
Wallace's "Island Life," 1880.)

Pen-y-Bryn, St. Peter's Road, Croydon, November 8th, 1880.

Many thanks for your kind remarks and notes on my book. Several of the
latter will be of use to me if I have to prepare a second edition, which I
am not so sure of as you seem to be.

1. In your remark as to the doubtfulness of paucity of fossils being due
to coldness of water, I think you overlook that I am speaking only of water
in the latitude of the Alps, in Miocene and Eocene times, when icebergs and
glaciers temporarily descended into an otherwise warm sea; my theory being
that there was no Glacial epoch at that time, but merely a local and
temporary descent of the snow-line and glaciers owing to high excentricity
and winter in aphelion.

2. I cannot see the difficulty about the cessation of the Glacial period.

Between the Miocene and the Pleistocene periods geographical changes
occurred which rendered a true Glacial period possible with high
excentricity. When the high excentricity passed away the Glacial epoch
also passed away in the temperate zone; but it persists in the arctic zone,
where, during the Miocene, there were mild climates, and this is due to the
persistence of the changed geographical conditions. The present arctic
climate is itself a comparatively new and abnormal state of things, due to
geographical modification.