Steve Irwin, a.k.a. the Crocodile Hunter, is a pretty big star these days. So it isn't surprising that Australia Zoo, the wildlife park he owns near Queensland's Sunshine Coast, markets itself intensely as "the home of the Crocodile Hunter." For evolutionary biologists, however, there's a potentially much more exciting character living at the park: Harriet, a wizened old Galapagos tortoise whose 175th birthday is being celebrated this year. If the stories told about her are true, then she's probably the only living creature to have come into personal contact with the ultimate biological celebrity – Charles Darwin.