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Darwin Correspondence Project

From W. C. L. Martin   [1859–61]1

– – & that their loss, or semiobliteration has resulted first from a combination of circumstances, bringing Disuse into play as an active agent,= 2dly by a perpetuation of the misfortune by inheritance,—till what was first accidental becomes normal— Now if the darkness of habitual residential places,— (burrows deep caves & the like), produces this effect in certain cases, why not in all where the like causes prevail?— But such is not the case.2

Look for example at your little Tuco=Tuco—(Ctenomys Brasiliensis)—3 this subterranean creature is not blind, although it often loses its sight by disease—(as the English soldiers in Egypt lost theirs from the irritation of impalpable sand)—nor is our mole,—although, if I remember rightly its optic nerve is either rudimentary or wanting, a fibril of the 5th pair appearing to supply its place— neither is the Hamster blind= But the Diplostoma which lives under ground, on roots, in the plains of the Missouri, appears to be so,—its eyes being covered by hair—4

In the Bathyergus, of the Cape, the eyes are uncovered, though very minute—5

In the Mole-rat of Asia minor—& the steppes of Tartary—(Asphalax Typhlus, Desmarest) the specks representing eyes are concealed beneath the skin—this subterreous creature is truly sightless—6

If we turn from these rodents to certain burrow dwelling Insectivora we shall find that eyes, though often very minute are not wanting— we may instance our shrew mouse (Sorex)—the Desman (Mygale G. Cuv:) of Muscovy, (also Pyrennees) in the Talposorex of N: America in the Cape Chrysochloris, & the Condylura of N. Amer. &c.—7

Now may we not rather attribute the non=developement or even nullity of eyes in these & other instances, to non=necessity for them, their presence in perfection being of no service, than to Disuse, which latter seems to me to say that eyes were once in perfection—whereas I think they have been stinted or arrested in their development, nature never wasting her resources,—& therefore stopping where her end is accomplished.— I am not however dogmatic on this point— Much may be said on both sides.—

But let us return to your Tucotuco (so interestingly described in your Journal8 a work more delightful to me than any work of the kind I have ever read, & a model for travelling naturalists)— Let us, I say return to your Tucotuco— We learn (& I remember examining the specimen dissected by Mr Reid)9 that its thigh bone is destitute of the Ligamentum teres,— accounting for its queer movements.— Now this ligament is wanting in very few mammals,—(but I am not aware of its absence in any birds) among which are four of very different character—viz the Orang, & the Elephant—The Seal tribe & the 3=toed Sloth. (I have mislaid my notes on this subject, & therefore hesitate to name any others)—

What are we to say respecting this absence, in such diverse examples.— now Animals as ponderous & lourd in motion as the Elephant, as good climbers as the orang & as efficient burrowers as the Tucotuco, do possess this ligament (so needful in man) thoroughly developed— Surely we cannot attribute these respective deficiencies to Disuse— Is it not because there is here no need of this ligament, or perhaps that it would be worse than unserviceable that Nature has not given it?— Is there not a negation in nature, when a priori, we should not anticipate (scrutiny alone teaching us) such a structural peculiarity.— Consider the double cæcum of Birds (present & single in man the Orang & one or two more)— Does not anatomy reveal strange facts? structural facts which we cannot, as I think attribute to disuse—& totality of anatomical structure must be the basis of our speculations— Can Disuse thoroughly alter the great points of anatomy— or take away the cells of the camel’s stomach in that of the ox?— In this latter instance has natural selection obtained & perpetuated them?—that is in the Camel— most probably—

But then what shall we say to the Ligamentum teres?— Has Natural Selection adopted it in the majority of mammals, & neglected it in the few;—or has Disuse, or the non=necessity of it operated so as to prevent its development= Is Natural selection confined only to adoption? or does it involve rejection?—

CD annotations

1.1 & that … the case 1.6] ‘Ch VII’ red crayon
1.1 & that … pair appearing 2.5] crossed pencil
6.1 Now … sides.— 6.7] ‘Ch VI   W. C. L. Martin’ red crayon
9.1 Has natural … rejection?— 9.4] scored red crayon

Footnotes

The date range is established by the references to Origin or Origin 2d ed., published in 1859 and 1860, respectively; the page references given by Martin could not be to the third edition, which was published in 1861.
CD discussed the effects of use and disuse in Origin, pp. 134–9.
Ctenomys, the tuco-tuco (Nowak 1999), a burrowing rodent from South America, is described in Origin, p. 137, as an example of blindness ‘probably due to gradual reduction from disuse, but aided perhaps by natural selection’. CD also discussed the tuco-tuco in Journal of researches, pp. 58–60.
Martin refers to the sight of several burrowing animals, including the genus then called Diplostoma.
Martin refers to Bathyergus, the dune mole-rat (Nowak 1999, 2: 1640–1).
Martin refers to what was then called Asphalax or Aspalax, and is now called Spalax, the Ukrainian blind mole-rat; this genus includes a species from eastern Ukraine and south-eastern Russia (Nowak 1999, 2: 1426–7). CD referred to the blindness of ‘Aspalax’ in Journal of researches 2d ed., p. 52. See also Keynes ed. 2000, pp. 165–6, 231.
Martin refers to several insectivores by their contemporary generic names, including the Russian desman (now Desman), the Pyrennean desman (now Galemys), and the Condylura, or star-nosed mole (Nowak 1999, 1: 230–3, 242–3).
Journal of researches, pp. 58–60.
The dissection of the tuco-tuco by Mr Reid is described in Journal of researches, pp. 59–60; in a letter to Jeffries Wyman, 3 October 1860 (Correspondence vol. 8), CD said that the dissection of the eyes had been carried out by ‘a clever young Surgeon’. He was presumably the James Reid who contributed ‘Notes on several quadrupeds in Mr. Darwin’s collection’ to the Proceedings of the Zoological Society of London 5 (1837): 4, but these notes did not mention Ctenomys brasiliensis. Reid has not been further identified.

Summary

Examples of animals that dwell in dark places, some of which are blind, some not. Asks: where causes are the same, why is not the effect? Does not think disuse is the answer, but arrested development.

Comments also on the absence of a ligament in four mammals and asks how natural selection accounts for this.

Letter details

Letter no.
DCP-LETT-2629
From
William Charles Linnaeus Martin
To
Charles Robert Darwin
Sent from
unstated
Source of text
DAR 47: 211–13
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 2629,” accessed on 23 October 2019, https://www.darwinproject.ac.uk/letter/DCP-LETT-2629.xml

Also published in The Correspondence of Charles Darwin, vol. 13 (Supplement)

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