The Romantic cult of the fragment lurks behind the contemporary fashion for books with preposterous possessive titles like Wittgenstein’s Poker, Churchill’s Cigar, Napoleon’s Buttons, Michelangelo’s Nose, Rembrandt’s Nose and Nathaniel’s Nutmeg. Just as the anatomist Georges Cuvier (1769–1832) claimed that he could reconstruct an entire animal from a single bone, and the connoisseur Giovanni Morelli (1816–91) believed he could attribute paintings from ‘marginal’ features like ears, hands and fingernails, so our authors insist that a seemingly inconsequential or bathetic detail is in fact the key to a whole personality or historical period.

The neuroscientist and philosopher Raymond Tallis is a follower of Cuvier, insofar as he believes that our essential humanity can, as it were, be ‘read off’ from individual physical components. Previously, he devoted an entire book to the human thumb, which by virtue of being fully opposable enabled