By The Associated Press

LONDON - British authorities say they're searching for a leather-bound notebook Charles Darwin used in developing his theory of natural selection.

English Heritage made the appeal Tuesday - the 150th anniversary of the publication of Darwin's "On the Origin of Species." English Heritage says thieves stole the notes in the 1970s or 1980s.

Darwin used the journal on a 1835 visit to the Galapagos Islands. It contains handwritten notes later developed into Darwin's book, the basis for the modern understanding of evolution.

A rare first edition of "Origin of Species" sold Tuesday at auction for 103,250 pounds ($172,000). London's Christie's auction house said it had languished for years on a toilet bookshelf.

This year marked the 200th anniversary of Darwin's birth.

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On the Net:

Darwin's Collected Works: http://darwin-online.org.uk/