Ɛpsilon

To George Howard Darwin   [1866]

Dear George

Can you or any of your friends answer me this.1 In a family of 10 5 of the children squinted & 5 did not & they came alternately—.2 But you must understand it is indifferent whether a squinter or a non squinter comes first. What I want to know is what are the chances against their coming alternately.3

Yours affec | Ch. Darwin | Ch. Darwin | Ch. Darwin4

P.S This case of the squinting & other such cases are real.

L(S)

Endorsement: ‘’66’

1
George Darwin was studying mathematics at Cambridge University (Alum. Cantab.).
2
A case of squinting in five of ten siblings was reported in Streatfield 1857–9, and was referred to in Sedgwick 1861, which CD cited (in relation to a different subject) in Variation 2: 328 n. However, Streatfield stated that squinting affected only the boys among ten siblings, not that alternate children squinted. CD briefly discussed squinting in Variation 2: 9, in the chapter on inheritance, but relied exclusively on evidence provided by William Bowman.
3
At the top of the letter, George calculated a 1:126 chance of squinters and non-squinters being born alternately in a family of ten, by dividing twice the square of the factorial of five by the factorial of ten. At the end of his working, he multiplied 126 by two; the reason for this is unclear. George’s reply to CD has not been found.
4
The letter is in the hand of CD’s daughter Elizabeth. The signatures are copied from CD’s own.

Please cite as “DCP-LETT-4961,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4961