To Francis Darwin 22 April [1871?]1
Down. | Beckenham | Kent. S.E.
My dear Frank
Please to thank Mr. Jackson very sincerely about the shrugging; the case as he remarks seems hardly distinct enough.2 Pray also thank him about the hands in prayer I am glad to find that this gesture is not innate. In this respect it is like kissing, whereas shrugging is certainly innate or instinctive. As I have just attended to Hobbes about laughter I shall now from what Mr. Jackson says omit this allusion.3 Tylor in his Early Hist of Mankind discusses gestures like that of ciconia, but I do not think throws much light on them.4
I can explain very little about laughter. It certainly seems to be originally merely the sign of enjoyment or happiness. Why any sound is uttered under this state of feeling I think I can dimly understand; but why this peculiar sound & no other is uttered I cannot say,—excepting that in a very general principle the sound would be very difft. from that of a scream or cry of pain. Our laughter, however, is closely analogous with the sound made by several monkeys when pleased, & the expression of their faces is then to a large extent the same as ours, owing to the contraction of apparently the same muscles. Why after early years of childhood laughter is chiefly, but not exclusively, excited by the ludicrous I do not understand, any more than why tickling excites laughter. I have sometimes fancied that it is more than a mere metaphor when we say that our minds are tickled by something ludicrous. The reason why with all races of men tears stream down the face during excessive laughter is I believe explicable on directly physical grounds, but too long to be here explained.5
Yours affectly | Ch. Darwin
P.S. What note on the flute makes you contract your platysma6
Please thank Mr Jackson for facts about shrugging, but case not distinct enough. Gestures associated with laughter. Platysma.