More Letters of Charles Darwin Volume I

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Your ever faithful and now very old pupil,
CHARLES DARWIN.

LETTER 251. TO J. TRAHERNE MOGGRIDGE.
Sevenoaks, October 9th [1872].

I have just received your note, forwarded to me from my home. I thank you
very truly for your intended present, and I am sure that your book will
interest me greatly. I am delighted that you have taken up the very
difficult and most interesting subject of the habits of insects, on which
Englishmen have done so little. How incomparably more valuable are such
researches than the mere description of a thousand species! I daresay you
have thought of experimenting on the mental powers of the spiders by fixing
their trap-doors open in different ways and at different angles, and
observing what they will do.

We have been here some days, and intend staying some weeks; for I was quite
worn out with work, and cannot be idle at home.

I sincerely hope that your health is not worse.

LETTER 252. TO A. HYATT.

(252/1. The correspondence with Professor Hyatt, of Boston, U.S.,
originated in the reference to his and Professor Cope's theories of
acceleration and retardation, inserted in the sixth edition of the
"Origin," page 149.

Mr. Darwin, on receiving from Mr. Hyatt a copy of his "Fossil Cephalopods
of the Museum of Comparative Zoology. Embryology," from the "Bull. Mus.
Comp. Zool." Harvard, Volume III., 1872, wrote as follows (252/2. Part of
this letter was published in "Life and Letters," III., page 154.):--)

October 10th, 1872.

I am very much obliged to you for your kindness in having sent me your
valuable memoir on the embryology of the extinct cephalopods. The work
must have been one of immense labour, and the results are extremely
interesting. Permit me to take this opportunity to express my sincere
regret at having committed two grave errors in the last edition of my
"Origin of Species," in my allusion to yours and Professor Cope's views on
acceleration and retardation of development. I had thought that Professor
Cope had preceded you; but I now well remember having formerly read with
lively interest, and marked, a paper by you somewhere in my library, on
fossil cephalopods, with remarks on the subject. (252/3. The paper seems
to be "On the Parallelism between the Different Stages of Life in the
Individual and those in the Entire Group of the Molluscous Order
Tetrabranchiata," from the "Boston. Soc. Nat. Hist. Mem." I., 1866-69, page
193. On the back of the paper is written, "I cannot avoid thinking this
paper fanciful.") It seems also that I have quite misrepresented your
joint view; this has vexed me much. I confess that I have never been able
to grasp fully what you wish to show, and I presume that this must be owing
to some dulness on my part...As the case stands, the law of acceleration
and retardation seems to me to be a simple [?] statement of facts; but the
statement, if fully established, would no doubt be an important step in our
knowledge. But I had better say nothing more on the subject, otherwise I
shall perhaps blunder again. I assure you that I regret much that I have
fallen into two such grave errors.

LETTER 253. A. HYATT TO CHARLES DARWIN.

(253/1. Mr. Hyatt replied in a long letter, of which only a small part is
here given.

Cannstadt bei Stuttgart, November 1872.

The letter with which you have honoured me, bearing the date of October
10th, has just reached here after a voyage to America and back.

I have long had it in mind to write you upon the subject of which you
speak, but have been prevented by a very natural feeling of distrust in the
worthiness and truth of the views which I had to present.

There is certainly no occasion to apologise for not having quoted my paper.
The law of acceleration and retardation of development was therein used to
explain the appearance of other phenomena, and might, as it did in nearly
all cases, easily escape notice.

My relations with Prof. Cope are of the most friendly character; and
although fortunate in publishing a few months ahead, I consider that this
gives me no right to claim anything beyond such an amount of participation
in the discovery, if it may be so called, as the thoroughness and worth of
my work entitles me to...

The collections which I have studied, it will be remembered, are fossils
collected without special reference to the very minute subdivisions, such
as the subdivisions of the Lower or Middle Lias as made by the German
authors, especially Quenstedt and Oppel, but pretty well defined for the
larger divisions in which the species are also well defined. The condition
of the collections as regards names, etc., was chaotic, localities alone,
with some few exceptions, accurate. To put this in order they were first
arranged according to their adult characteristics. This proving
unsatisfactory, I determined to test thoroughly the theory of evolution by
following out the developmental history of each species and placing them
within their formations, Middle or Upper Lias, Oolite or so, according to
the extent to which they represented each other's characteristics. Thus an
adult of simple structure being taken as the starting-point which we will
call a, another species which was a in its young stage and became b in the
adult was placed above it in the zoological series. By this process I
presently found that a, then a b and a b c, c representing the adult stage,
were very often found; but that practically after passing these two or
three stages it did not often happen that a species was found which was a b
c in the young and then became d in the adult. But on the other hand I
very frequently found one which, while it was a in the young, skipped the
stages b and c and became d while still quite young. Then sometimes,
though more rarely, a species would be found belonging to the same series,
which would be a in the young and with a very faint and fleeting
resemblance to d at a later stage, pass immediately while still quite young
to the more advanced characteristics represented by e, and hold these as
its specific characteristics until old age destroyed them. This skipping
is the highest exemplification, or rather manifestation, of acceleration in
development. In alluding to the history of diseases and inheritance of
characteristics, you in your "Origin of Species" allude to the ordinary
manifestation of acceleration, when you speak of the tendency of diseases
or characteristics to appear at younger periods in the life of the child
than of its parents. This, according to my observations, is a law, or
rather mode, of development, which is applicable to all characteristics,
and in this way it is possible to explain why the young of later-occurring
animals are like the adult stages of those which preceded them in time. If
I am not mistaken you have intimated something of this sort also in your
first edition, but I have not been able to find it lately. Of course this
is a very normal condition of affairs when a series can be followed in this
way, beginning with species a, then going through species a b to a b c,
then a b d or a c d, and then a d e or simply a e, as it sometimes comes.
Very often the acceleration takes place in two closely connected series,
thus:

a--ab--abd--ae
---ad

in which one series goes on very regularly, while another lateral offshoot
of a becomes d in the adult. This is an actual case which can be plainly
shown with the specimens in hand, and has been verified in the collections
here. Retardation is entirely Prof. Cope's idea, but I think also easily
traceable. It is the opponent of acceleration, so to speak, or the
opposite or negative of that mode of development. Thus series may occur in
which, either in size or characteristics, they return to former
characteristics; but a better discussion of this point you will find in the
little treatise which I send by the same mail as this letter, "On
Reversions among the Ammonites."

LETTER 254. TO A. HYATT.
Down, December 4th, 1872.

I thank you sincerely for your most interesting letter. You refer much too
modestly to your own knowledge and judgment, as you are much better fitted
to throw light on your own difficult problems than I am.

It has quite annoyed me that I do not clearly understand yours and Prof.
Cope's views (254/1. Prof. Cope's views may be gathered from his "Origin
of the Fittest" 1887; in this book (page 41) is reprinted his "Origin of
Genera" from the "Proc. Philadelph. Acad. Nat. Soc." 1868, which was
published separately by the author in 1869, and which we believe to be his
first publication on the subject. In the preface to the "Origin of the
Fittest," page vi, he sums up the chief points in the "Origin of Genera"
under seven heads, of which the following are the most important:--"First,
that development of new characters has been accomplished by an ACCELERATION
or RETARDATION in the growth of the parts changed...Second, that of EXACT
PARALLELISM between the adult of one individual or set of individuals, and
a transitional stage of one or more other individuals. This doctrine is
distinct from that of an exact parallelism, which had already been stated
by von Baer." The last point is less definitely stated by Hyatt in his
letter of December 4th, 1872. "I am thus perpetually led to look upon a
series very much as upon an individual, and think that I have found that in
many instances these afford parallel changes." See also "Lamarck the
Founder of Evolution, by A.S. Packard: New York, 1901.) and the fault lies
in some slight degree, I think, with Prof. Cope, who does not write very
clearly. I think I now understand the terms "acceleration" and
"retardation"; but will you grudge the trouble of telling me, by the aid of
the following illustration, whether I do understand rightly? When a fresh-
water decapod crustacean is born with an almost mature structure, and
therefore does not pass, like other decapods, through the Zoea stage, is
this not a case of acceleration? Again, if an imaginary decapod retained,
when adult, many Zoea characters, would this not be a case of retardation?
If these illustrations are correct, I can perceive why I have been so dull
in understanding your views. I looked for something else, being familiar
with such cases, and classing them in my own mind as simply due to the
obliteration of certain larval or embryonic stages. This obliteration I
imagined resulted sometimes entirely from that law of inheritance to which
you allude; but that it in many cases was aided by Natural Selection, as I
inferred from such cases occurring so frequently in terrestrial and fresh-
water members of groups, which retain their several embryonic stages in the
sea, as long as fitting conditions are present.

Another cause of my misunderstanding was the assumption that in your series

a--ab--abd--ae,
--------ad

the differences between the successive species, expressed by the terminal
letter, was due to acceleration: now, if I understand rightly, this is not
the case; and such characters must have been independently acquired by some
means.

The two newest and most interesting points in your letter (and in, as far
as I think, your former paper) seem to me to be about senile
characteristics in one species appearing in succeeding species during
maturity; and secondly about certain degraded characters appearing in the
last species of a series. You ask for my opinion: I can only send the
conjectured impressions which have occurred to me and which are not worth
writing. (It ought to be known whether the senile character appears before
or after the period of active reproduction.) I should be inclined to
attribute the character in both your cases to the laws of growth and
descent, secondarily to Natural Selection. It has been an error on my
part, and a misfortune to me, that I did not largely discuss what I mean by
laws of growth at an early period in some of my books. I have said
something on this head in two new chapters in the last edition of the
"Origin." I should be happy to send you a copy of this edition, if you do
not possess it and care to have it. A man in extreme old age differs much
from a young man, and I presume every one would account for this by failing
powers of growth. On the other hand the skulls of some mammals go on
altering during maturity into advancing years; as do the horns of the stag,
the tail-feathers of some birds, the size of fishes etc.; and all such
differences I should attribute simply to the laws of growth, as long as
full vigour was retained. Endless other changes of structure in successive
species may, I believe, be accounted for by various complex laws of growth.
Now, any change of character thus induced with advancing years in the
individual might easily be inherited at an earlier age than that at which
it first supervened, and thus become characteristic of the mature species;
or again, such changes would be apt to follow from variation, independently
of inheritance, under proper conditions. Therefore I should expect that
characters of this kind would often appear in later-formed species without
the aid of Natural Selection, or with its aid if the characters were of any
advantage. The longer I live, the more I become convinced how ignorant we
are of the extent to which all sorts of structures are serviceable to each
species. But that characters supervening during maturity in one species
should appear so regularly, as you state to be the case, in succeeding
species, seems to me very surprising and inexplicable.

With respect to degradation in species towards the close of a series, I
have nothing to say, except that before I arrived at the end of your
letter, it occurred to me that the earlier and simpler ammonites must have
been well adapted to their conditions, and that when the species were
verging towards extinction (owing probably to the presence of some more
successful competitors) they would naturally become re-adapted to simpler
conditions. Before I had read your final remarks I thought also that
unfavourable conditions might cause, through the law of growth, aided
perhaps by reversion, degradation of character. No doubt many new laws
remain to be discovered. Permit me to add that I have never been so
foolish as to imagine that I have succeeded in doing more than to lay down
some of the broad outlines of the origin of species.

After long reflection I cannot avoid the conviction that no innate tendency
to progressive development exists, as is now held by so many able
naturalists, and perhaps by yourself. It is curious how seldom writers
define what they mean by progressive development; but this is a point which
I have briefly discussed in the "Origin." I earnestly hope that you may
visit Hilgendorf's famous deposit. Have you seen Weismann's pamphlet
"Einfluss der Isolirung," Leipzig, 1872? He makes splendid use of
Hilgendorf's admirable observations. (254/2. Hilgendorf, "Monatsb. K.
Akad." Berlin, 1866. For a semi-popular account of Hilgendorf's and
Hyatt's work on this subject, see Romanes' "Darwin and after Darwin," I.,
page 201.) I have no strength to spare, being much out of health;
otherwise I would have endeavoured to have made this letter better worth
sending. I most sincerely wish you success in your valuable and difficult
researches.

I have received, and thank you, for your three pamphlets. As far as I can
judge, your views seem very probable; but what a fearfully intricate
subject is this of the succession of ammonites. (254/3. See various
papers in the publications of the "Boston Soc. Nat. Hist." and in the
"Bulletin of the Harvard Museum of Comp. Zoology.")

LETTER 255. A. HYATT TO CHARLES DARWIN.
Cannstadt bei Stuttgart, December 8th, 1872.

The quickness and earnestness of your reply to my letter gives me the
greatest encouragement, and I am much delighted at the unexpected interest
which your questions and comments display. What you say about Prof. Cope's
style has been often before said to me, and I have remarked in his writings
an unsatisfactory treatment of our common theory. This, I think, perhaps
is largely due to the complete absorption of his mind in the contemplation
of his subject: this seems to lead him to be careless about the methods in
which it may be best explained. He has, however, a more extended knowledge
than I have, and has in many ways a more powerful grasp of the subject, and
for that very reason, perhaps, is liable to run into extremes. You ask
about the skipping of the Zoea stage in fresh-water decapods: is this an
illustration of acceleration? It most assuredly is, if acceleration means
anything at all. Again, another and more general illustration would be,
if, among the marine decapods, a series could be formed in which the Zoea
stage became less and less important in the development, and was relegated
to younger and younger stages of the development, and finally disappeared
in those to which you refer. This is the usual way in which the
accelerated mode of development manifests itself; though near the lowest or
earliest occurring species it is also to be looked for. Perhaps this to
which you allude is an illustration somewhat similar to the one which I
have spoken of in my series,

a--ab--abc--ae
--------ad,

which like "a d" comes from the earliest of a series, though I should think
from the entire skipping of the Zoea stage that it must be, like "a e," the
result of a long line of ancestors. In fact, the essential point of our
theory is, that characteristics are ever inherited by the young at earlier
periods than they are assumed in due course of growth by the parents, and
that this must eventually lead to the extinction or skipping of these
characteristics altogether...

Such considerations as these and the fact that near the heads of series or
near the latest members of series, and not at the beginning, were usually
found the accelerated types, which skipped lower characteristics and
developed very suddenly to a higher and more complex standpoint in
structure, led both Cope and [myself] into what may be a great error. I
see that it has led you at least into the difficulty of which you very
rightly complain, and which, I am sorry to see, has cost you some of your
valuable time. We presumed that because characteristics were perpetually
inherited at earlier stages, that this very concentration of the developed
characteristics made room for the production of differences in the adult
descendants of any given pair. Further, that in the room thus made other
different characteristics must be produced, and that these would
necessarily appear earlier in proportion as the species was more or less
accelerated, and be greater or less in the same proportion. Finally, that
in the most accelerated, such as "a c" or "a d," the difference would be so
great as to constitute distinct genera. Cope and I have differed very
much, while he acknowledged the action of the accumulated mode of
development only when generic characteristics or greater differences were
produced, I saw the same mode of development to be applicable in all cases
and to all characteristics, even to diseases. So far the facts bore us
out, but when we assumed that the adult differences were the result of the
accelerated mode of development, we were perhaps upon rather insecure
ground. It is evidently this assumption which has led you to misunderstand
the theory. Cope founded his belief, that the adult characteristics were
also the result of acceleration, if I rightly remember it, mainly upon the
class of facts spoken of above in man where a sudden change into two organs
may produce entirely new and unexpected differences in the whole
organisation, and upon the changes which acceleration appeared to produce
in the development of each succeeding species. Your difficulty in
understanding the theory and the observations you have made show me at once
what my own difficulties have been, but of these I will not speak at
present, as my letter is spinning itself out to a fearful length.

(255/1. After speaking of Cope's comparison of acceleration and
retardation in evolution to the force of gravity in physical matters Mr.
Hyatt goes on:--)

Now it [acceleration] seems to me to explain less and less the origin of
adult progressive characteristics or simply differences, and perhaps now I
shall get on faster with my work.

LETTER 256. TO A. HYATT.
Down, December 14th [1872].

(256/1. In reply to the above letter (255) from Mr. Hyatt.)

Notwithstanding the kind consideration shown in your last sentence, I must
thank you for your interesting and clearly expressed letter. I have
directed my publisher to send you a copy of the last edition of the
"Origin," and you can, if you like, paste in the "From the Author" on next
page. In relation to yours and Professor Cope's view on "acceleration"
causing a development of new characters, it would, I think, be well if you
were to compare the decapods which pass and do not pass through the Zoea
stage, and the one group which does (according to Fritz Muller) pass
through to the still earlier Nauplius stages, and see if they present any
marked differences. You will, I believe, find that this is not the case.
I wish it were, for I have often been perplexed at the omission of
embryonic stages as well as the acquirement of peculiar stages appearing to
produce no special result in the mature form.

(256/2. The remainder of this letter is missing, and the whole of the last
sentence is somewhat uncertainly deciphered. (Note by Mr. Hyatt.))

LETTER 257. TO A. HYATT.
Down, February 13th, 1877.

I thank you for your very kind, long, and interesting letter. The case is
so wonderful and difficult that I dare not express any opinion on it. Of
course, I regret that Hilgendorf has been proved to be so greatly in error
(257/1. This refers to a controversy with Sandberger, who had attacked
Hilgendorf in the "Verh. der phys.-med. Ges. zu Wurzburg," Bd. V., and in
the "Jahrb. der Malakol. Ges." Bd. I., to which Hilgendorf replied in the
"Zeitschr. d. Deutschen geolog. Ges." Jahrb. 1877. Hyatt's name occurs in
Hilgendorf's pages, but we find no reference to any paper of this date; his
well-known paper is in the "Boston. Soc. Nat. Hist." 1880. In a letter to
Darwin (May 23rd, 1881) Hyatt regrets that he had no opportunity of a third
visit to Steinheim, and goes on: "I should then have done greater justice
to Hilgendorf, for whom I have such a high respect."), but it is some
selfish comfort to me that I always felt so much misgiving that I never
quoted his paper. (257/2. In the fifth edition of the "Origin" (page
362), however, Darwin speaks of the graduated forms of Planorbis
multiformis, described by Hilgendorf from certain beds in Switzerland, by
which we presume he meant the Steinheim beds in Wurtemberg.) The
variability of these shells is quite astonishing, and seems to exceed that
of Rubus or Hieracium amongst plants. The result which surprises me most
is that the same form should be developed from various and different
progenitors. This seems to show how potent are the conditions of life,
irrespectively of the variations being in any way beneficial.

The production of a species out of a chaos of varying forms reminds me of
Nageli's conclusion, as deduced from the study of Hieracium, that this is
the common mode in which species arise. But I still continue to doubt much
on this head, and cling to the belief expressed in the first edition of the
"Origin," that protean or polymorphic species are those which are now
varying in such a manner that the variations are neither advantageous nor
disadvantageous. I am glad to hear of the Brunswick deposit, as I feel
sure that the careful study of such cases is highly important. I hope that
the Smithsonian Institution will publish your memoir.

LETTER 258. TO A. DE CANDOLLE.
Down, January 18th [1873].

It was very good of you to give up so much of your time to write to me your
last interesting letter. The evidence seems good about the tameness of the
alpine butterflies, and the fact seems to me very surprising, for each
butterfly can hardly have acquired its experience during its own short
life. Will you be so good as to thank M. Humbert for his note, which I
have been glad to read. I formerly received from a man, not a naturalist,
staying at Cannes a similar account, but doubted about believing it. The
case, however, does not answer my query--viz., whether butterflies are
attracted by bright colours, independently of the supposed presence of
nectar?

I must own that I have great difficulty in believing that any temporary
condition of the parents can affect the offspring. If it last long enough
to affect the health or structure of the parents, I can quite believe the
offspring would be modified. But how mysterious a subject is that of
generation! Although my hypothesis of pangenesis has been reviled on all
sides, yet I must still look at generation under this point of view; and it
makes me very averse to believe in an emotion having any effect on the
offspring. Allow me to add one word about blushing and shyness: I
intended only to say the habit was primordially acquired by attention to
the face, and not that each shy man now attended to his personal
appearance.