Australopithecus afarensis is an extinct hominid which lived between 3.7 and 2.9 million years ago.[citation needed] A. afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A. afarensis was ancestral to both the genus Australopithecus and the genus Homo, which includes the modern human species, Homo sapiens. The most famous fossil is the partial skeleton named Lucy (3.2 million years old) by Donald Johanson and colleagues, after they played the Beatles song Lucy in the Sky with Diamonds over and over in celebration of their find. Johanson & Maitland 1981, pp. 283–297 Johanson, D.C. (2009). "Lucy (Australopithecus afarensis)". In Michael Ruse & Joseph Travis. Evolution: The First Four Billion Years. Cambridge, Massachusetts: The Belknap Press of Harvard University Press. pp. 693–697. ISBN 978-0-674-03175-3.  Wood, B.A. (1994). "Evolution of australopithecines". In Jones, S., Martin, R. & Pilbeam, D.. The Cambridge Encyclopedia of Human Evolution. Cambridge, U.K.: Cambridge University Press. ISBN 0-521-3270-3.  Also ISBN 0-521-46786-1 (paperback).