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Darwin Correspondence Project

From Lawson Tait   16 March [1875]1

7, Great Charles St. | Birmingham.

March 16

Dear Sir,

Thanks for your kind note. I shall send you a copy of my little paper.2

I am keeping a number of white mice to try to unravel the use of the peculiar tail of mice & rats but I am completely beaten3

My view does not preclude any other modification or use of the tail: but it seems to me to be important as illustrating how correlation of growth (that is thick fur leading to a bushy tail) will bring out a new circumstance favourable to survival & truly lead to a total alteration of some important habits—as the curling up of these animals when going to sleep4

Yours faithfully, | Lawson Tait

PS. I had missed the Yak in my search for animals with a bushy tail.5 But he has a long abdominal fringe of hair nearly touching the ground. When he lies down with his limbs drawn up to or under him, as all ruminants do, his tail & fringe would act as a railway rug, preventing loss of heat from the limbs & damage to them from frost bite—as the tissue outside the bone is thin & there is nothing but a rather weak circulation to resist loss of heat. He lives close to the line of perpetual snow—the very condition under which such an epithelial appendage would conduce to survival



The year is established by the relationship between this letter and the letter from Lawson Tait, 12 March [1875].
No copy of the paper Tait delivered at the Birmingham Natural History Society has been found in the Darwin Archive–CUL, but a summary was published in the Birmingham Daily Post, 8 April 1875, p. 5, and later reprinted in Hardwicke’s Science-Gossip in June 1875 (Tait 1875a); it included CD’s remarks from his letter to Tait of [13–15 March 1875].
Tait wanted to determine the use of tails in different animals (see letter from Lawson Tait, 12 March [1875]). In the published summary, Tait concluded that he had yet to find a reasonable explanation for the tails of rats and mice (Tait 1875a, p. 127).
In his letter to CD of 12 March [1875], Tait hypothesised that the bushy tails of some animals helped to retain heat when the animal was curled up.
In his letter to Tait of [13–15 March 1875], CD had mentioned the hairy tail of the yak, wondering whether it served any purpose other than as a fly-flapper.


Uses of tails of mice. Functions of tails generally.

Letter details

Letter no.
Robert Lawson (Lawson) Tait
Charles Robert Darwin
Sent from
Source of text
DAR 178: 3
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9889,” accessed on 25 October 2021,

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