England ? An auction house says it is selling a rare first edition of Charles Darwin’s “On the Origin of Species” found in a family’s guest lavatory in southern England.

Christie’s auction house said Sunday the book — one of around 1,250 copies first printed in 1859 — had been on a toilet bookshelf at a family’s home in Oxford.

The book will be auctioned on Tuesday, the 150th anniversary of the publication of the famous work. Christie’s said the book is likely to sell for around $100,000.

Darwin’s “The Origin of Species” outlined his theory of natural selection, the foundation for the modern understanding of evolution.

Celebrations around the world this year have marked the 200th anniversary of Darwin’s birth.