From James Gibb   23 February 1875

Sir.

I think I have seen in the conduct of my little son, 7 months old, the origin of the shake of the head, as signifying “no”.

Within the last few days, for the first time in his life, he has been unwell, & has refused food at meal hours. When the mouth-piece of the bottle has been put to his mouth he has turned from it as far as possible, & when it has followed his mouth he has turned his head in the opposite direction. He saw that the result of turning thus from the bottle was that the bottle was taken away; & after two days of illness as soon as he saw the bottle (if he did not want it) he shook his head; & now, within a week of the action being first observed, he uses it (exactly as if he had been taught by those about him) to let it be known he does not wish to eat, or be taken up or put down, as the case may be.¹

The nod may have come to signify assent either from the action & the sentiment being both the reverse of the shake & dissent, or it may be a corruption of the bow of submission

I do not know whether any explanation of these universal signs has been published.

Yours faithfy | Jas Gibb.

C. Darwin Esq