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Darwin Correspondence Project

From Alpheus Hyatt   8 January [1875]1

Boston Society of Natural History, | Berkeley, cor. of Boylston St. | Boston, Mass.,

Jan 8th 1874

Dear Sir

Since my return I have several times tempted to write you but refrained because it seemed to me I was not quite ready.2

You will see by the inclosed that I am going ahead a little. I think I have the facts to show the probability of the statements made   That which seems to me most important is the subordination of characteristics, those which are longest inherited being the most stable if not entirely independent of all influences of the surroundings, while those which are recently inherited in each group on the other hand seem to represent every geological change. It has also struck me, that this is the reason why the faunæ of any one geological epoch are generally similar; a certain uniformity of the conditions producing a certain uniformity of characteristics in every race however different structurally.

But this I am not prepared to follow out yet, though I think I could get a number of facts even now.

Then the distinctions made between the representative or parallel forms and the structural characteristics of the groups in which the forms appear, appears to me to be on the right road since it enables me to see clearly for the first time how and to what I can apply the law of natural selection. Perhaps it is all wrong and I have been in too much of a hurry, but I have held myself as long as it was possible and at last fairly gave it up as too difficult. The facts seem to me in their natural arrangment to indicate clearly, that we must divide characteristics into those which are almost independent of the influence of their surroundings, the embryonic; those which are peculiarly under their influence and which are the similarities or representative, or parallel characteristics or forms in distinct structural groups; and those which are evidently the result of natural selection. Of these last I only mention one set, those which constitute the differences of groups, but even these are traceable to varieties of species when followed out carefully. Of course I could not study those finer correspondences and structural characteristics which more immediately affect the life of the species within the time of one single fauna to any great extent and I had to content myself with the coarser materials.

Such as it is however I hope it will meet with your favorable notice as my other efforts have done. The paper in full will appear in the Memoirs but may not be out for a year yet so I send this newspaper slip.3 I remember with great pleasure my visit to your house and beg you will present my compliments to Mrs Darwin and your daughter4

Very respectfully | yours | A Hyatt




Professor Hyatt presented a paper on “Old Age Characteristics among Ammonites, and their bearing upon the question of Parallelisms and the Theory of Evolution.”

The speaker traced the history of the evolution of the order of Ammonoids, showing that the characteristics of the first three stages of the embryo were inherited from a very early period.

That these became invariable6 in the young as embryonic characteristics only after the lapse of time represented by the Silurian, Devonian, and Carboniferous periods. The variability of their appearance in the same species in the Silurian showed how recently they were inherited, and their invariable appearance in every individual of the Jurassic showed the result of the long ages of inheritance intervening between that period and the Silurian epoch.

He then showed that in each subordinate group there were certain invariably occurring forms precisely similar to those found in other groups often widely removed in time and very distinct in the structure of the parts.

These parallel7 forms of every group begin with a certain low or open-whorled form and evolve in course of time and by inheritance more and involved or modified whorls. This and the origin of most of the groups from certain single ancestral species of the dicordal or open-whorled forms show conclusively that these forms arise independently in each group. They are the mechanical results of the growth or increase in size of the shell of the common embryonic form of the third stage.

This growth is due to the favorable nature of the physical surroundings, primarily producing characteristic changes which become perpetuated and increased by inheritance within the group. Besides these there are other parallel forms in the same groups which may be shown to be due to the inheritance of the old age of these same parallel forms, and, by comparison with similar forms prematurely produced in the different species by disease or local influences, may be attributed to the action of unfavorable surroundings.

The word surroundings is now used instead of environment, for the reason that environment covers the whole ground of physical causes which may have either a remote or immediate effect upon the life of the species.

The environment or the sum of the physical influences are perpetually immical8 to the prolonged existence of life, and bring about in the individual the retrograde metamorphoses known as old age, and leading to death by the disuse, atrophy and decay of the functions and organs.

These changes are in precise correspondence, and evidently acted upon in their transmission from individual to individual, during the decline of a group by the same law of inheritance as the other characteristics. It thus becomes safe to attribute the parallel modifications of forms whether during the progress or decline of the existence of a group to the direct influence of the environment or physical causes.

Besides these characteristic forms and structural parts which are parallels, there are many others in each group not classified under the head of similarities but under that of differences, in so far as they distinguish the groups from each other. These may be often followed back to varieties of one species, showing that certain varieties have given rise to the groups. These varieties are few as compared with the whole number of varieties traceable in these original ancestral species.

Thus it seems clear that the varieties which have developed into groups, had certain advantageous peculiarities, and that these were the structural differences which distinguished the groups from each other.

It may also be shown by Cope’s law of the origination of differences by growth9 that the origin of these differences probably lies in some law of growth under the influence of the physical surroundings, supply of and kind of food, climate, etc.

Thus they are due to growth modified and directed by the Darwinian law of natural selection, both of these being directly subject to the influence of10 this environment, or, the sum of all, the physical influences brought to bear upon the organization.

CD annotations

Top of letter: ‘On Variation of Ammonite in course of time’ ink


The year is established by the date of the enclosure. Hyatt wrote 1874 in error.
Hyatt had spent time in 1872 and 1873 near Stuttgart, studying the Steinheim fossils (see Correspondence vol. 20, letters from Alpheus Hyatt, [late] November 1872 and 8 December 1872, and Popular Science Monthly 78 (1911): 142).
An abstract of Hyatt’s memoir (longer than the newspaper article) was published in the Proceedings of the Boston Society of Natural History in 1875 (Hyatt 1874).
Hyatt refers to Emma Darwin and to Elizabeth Darwin, who was still living at home. It is not known when Hyatt visited Down.
The Evening Transcript was a Boston, Massachusetts, daily paper.
‘invariably’ in the printed text altered to ‘invariable’ by hand.
‘parallel’ inserted by hand.
Immical: a misprint for inimical.
Edward Drinker Cope explained generic differences between organisms as a consequence of acceleration or retardation of growth. In acceleration, an animal’s growth speeded up, so that more advanced characteristics were passed on to its offspring, and earlier stages might eventually be condensed or omitted; in retardation, growth slowed, so that only earlier stages of development were passed on to offspring (Cope 1871).
‘of’ inserted by hand over printed comma.


Cope, Edward Drinker. 1871. The method of creation of organic forms. [Read 15 December 1871.] Proceedings of the American Philosophical Society 12 (1871–2): 229–63.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Hyatt, Alpheus. 1874. Abstract of a memoir on the ‘Biological relations of the Jurassic ammonites’. [Read 16 December 1874.] Proceedings of the Boston Society of Natural History 17 (1874–5): 236–41.


Encloses report on his paper "Old age characteristics among ammonites", [Proc. Boston Soc. Nat. Hist. 17 (1875): 236–41].

Stability of long inherited characters. Dependence of some recently acquired characters on the environment.

Letter details

Letter no.
Alpheus Hyatt
Charles Robert Darwin
Sent from
Boston Society of Natural History
Source of text
DAR 166: 358
Physical description
4pp † enc

Please cite as

Darwin Correspondence Project, “Letter no. 9233,” accessed on 23 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 23