Darwin scholar John van Whye put this on Facebook: it’s Darwin’s only known depiction of himself. John’s notes:
Darwin sketched himself as this little stick man on the island of St Helena in July 1836 as the Beagle was sailing home. The sketch represents the strong winds blowing up the sea cliffs while the air on top of the cliff, where Darwin was standing, was perfectly still. Only by holding his arm out over the cliff could he detect the strong winds. The text reads “gale of wind to hand not to man”.
The sketch is in one of Darwin’s Beagle field notebooks, the Despoblado notebook, here.
See a drawing of the cliffs from a later illustrated edition of voyage of the Beagle, here.
h/t: Matthew Cobb, David Bressan