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Darwin Correspondence Project

To Alpheus Hyatt   10 October [1872]1

Down, | Beckenham, Kent. [Sevenoaks, Kent.]

Oct. 10th

Dear Sir

I am very much obliged to you for your kindness in having sent me your valuable memoir on the embryology of the extinct cephalopods.2 The work must have been one of immense labour & 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 your & Prof. Cope’s views on the acceleration & retardation of development.3 I had thought that Prof. Cope had preceded you; but I now well remember having formerly read with lively interest & marked a paper by you (somewhere in my Library) on fossil Cephalopods with remarks on the subject.4 It seems, also, that I have quite misrepresented your joint view.5 This has vexed me much. I confess that I have never been able fully to grasp what you wish to show, & I presume this must be owing to some dullness on my part.— I assumed, though I had no right to make any such assumption, that the kind of explanation which I have given, was what you intended. As the case stands, the law of acceleration & 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, & with much respect, I remain Dear Sir | Yours faithfully | Ch. Darwin


The year is established by the reference to Hyatt’s article (see n. 2, below).
The reference is to Hyatt’s ‘Fossil cephalopods of the Museum of Comparative Zoology. Embryology’ (Hyatt 1872). CD’s annotated presentation copy is in the Darwin Pamphlet Collection–CUL.
In Origin 6th ed., p. 149, CD discussed the acceleration and retardation of development and mentioned Edward Drinker Cope, but not Hyatt, as a proponent of the theory (see n. 5, below).
CD’s annotated copy of Hyatt’s earlier paper, ‘On the parallelism between the different stages of life in the individual and those in the entire group of the molluscous order Tetrabranchiata’ (Hyatt 1866) is in the Darwin Pamphlet Collection–CUL. Hyatt and Cope independently developed similar theories at about the same time, but Hyatt published his views earlier (see Pfeifer 1965, p. 157 and n. 5).
In Origin 6th ed., p. 149, CD had explained acceleration and retardation as the loss of certain characteristics in progeny when animals reproduced before they had acquired these characters, and he expressed doubt as to whether species had ever been modified in this way. Hyatt and Cope regarded acceleration as a process by which an animal’s growth speeded up, so that in reproduction more advanced traits would be passed on. Retardation was characterised by growth slowing and degraded characteristics being passed on. See Pfeifer 1965, p. 160.


Thanks for "Embryology of the fossil cephalopods", [Bull. Mus. Comp. Zool. Harvard 3 (1872–4): 59–112].

Regrets error in attributing acceleration concept to E. D. Cope instead of to AH in last edition of Origin, and misrepresentation of their joint view.

Letter details

Letter no.
Charles Robert Darwin
Alpheus Hyatt
Sent from
Sevenoaks Down letterhead
Source of text
Manuscripts Division, Department of Rare Books and Special Collections, Princeton University Library (Hyett and Mayer Collection)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8551,” accessed on 27 April 2017,

Also published in The Correspondence of Charles Darwin, vol. 20