To G. E. Shuttleworth   17 February [1874]¹

Dear Sir

My son George Darwin (who is a good mathematician, having been 2^nd. wrangler at Cambridge) has been at work for nearly a year in trying to discover, by several independent statistical methods, what proportion of all marriages are between first cousins; and he now feels pretty confident that his results will not be subject to an error of so much as one per cent.² He is being greatly aided in this part of his enquiry by D^r. Farre, the Registrar General.³ He now wishes to utilize these results by the disovery of what the proportion of the offspring of first cousin marriages may be amongst the insane, deaf and dumb, idiotic, blind &c. I have for 30 years considered an answer to this enquiry of importance. We have here, I think, the rare case of an enquiry, the answer to which will be of value, whatever it may be; for we shall either find that such marriages are injurious, or that they may be persevered in with impunity.

D^r. Crichton Brown, who has been at great pains to help my son, has been kind enough to permit me to use his name in introducing myself to you; and he appears to think it very likely that you will consider this enquiry of sufficient importance to be willing to aid my son by asking the patients in the asylum in which you are in attendance, either by means of assistants or personally, whether or not they are the offspring of first cousin marriages, and recording the answers.⁴ The question which my son proposes to ask is, Were your parents first cousins or not? The questioner will doubtless be the best judge of the most prudent way of approaching the subject, and of explaining the question in each individual case, and would be to a great extent able to judge of the trustworthiness of the answer from the known character of the patient.

If you should be willing to undertake this laborious task you would be conferring a very great favour both on my son and on myself; and I would beg you to send the results to him at Trinity College, Cambridge, where he is a resident fellow.

Would you have the kindness to add a general description of the rank of life from which the majority of your patients are drawn,— e.g. labourers and artizans,— shop-keeper and commercial,—upper ranks.

With apologies for my intrusion on you, | Believe me | Dear Sir | Yours faithfully, | Ch. Darwin

Feb. 17^th.