My dear Lubbock

As I hear that the Census will be brought before the House tomorrow, I write to say how much I hope that you will express your opinion on the desirability of queries in relation to consanguineous marriages being inserted.¹ As you are aware, I have made experiments on the subject during several years; & it is my clear conviction that there is now ample evidence of the existence of a great physiological law, rendering an enquiry with reference to mankind of much importance. In England & many parts of Europe the marriages of cousins are objected to from their supposed injurious consequences; but this belief rests on no direct evidence. It is therefore manifestly desirable that the belief should either be proved false, or should be confirmed, so that in this latter case the marriages of cousins might be discouraged.

If the proper queries are inserted, the returns would show whether married cousins have in their households on the night of the census as many children, as have parents who are not related; & should the number prove fewer, we might safely infer either lessened fertility in the parents, or which is more probable, lessened vitality in the offspring.

It is moreover much to be wished that the truth of the often repeated assertion that consanguineous marriages lead to deafness & dumbness, blindness &c, should be ascertained;² & all such assertions could be easily tested by the returns from a single census—

Believe me | yours very sincerely | Charles Darwin