Charles Darwin hid Behind his Wife Emma in Order to Deal With Private Correspondence from Patrick Matthew

"Mr Darwin begs me to thank you warmly for your letter which
 has interested him very much. I am sorry to say that he is so unwell
as not to be able to write himself."

Letter From Emma Darwin to Patrick Matthew   21 November 1863

Dear Sir

Mr Darwin begs me to thank you warmly for your letter which has interested him very much. I am sorry to say that he is so unwell as not to be able to write himself.

With regard to Natural Selection he says that he is not staggered by your striking remarks. He is more faithful to your own original child than you are yourself. He says you will understand what he means by the following metaphor.

Fragments of rock fallen from a lofty precipice assume an infinitude of shapes—these shapes being due to the nature of the rock, the law of gravity &c— by merely selecting the well-shaped stones & rejecting the ill-shaped an architect (called Nat. Selection could make many & various noble buildings.

Mr Darwin is much obliged to you for sending him your photograph. He wishes he could send you as good a one of himself. The enclosed was a good likeness taken by his eldest son but the impression is faint.

You express yourself kindly interested about his family. We have 5 sons & 2 daughters, of these 2 only are grown up.  Mr Darwin was very ill 2 months ago & his recovery is very slow, so that I am afraid it will be long before he can attend to any scientific subject.