Photo: Ardi's Secret: Did Early Humans Start Walking for Sex?
Editor's note: At the request of illustrator J.H. Matternes and Science/AAAS, we are removing the illustration of Ardipithecus ramidus that was once featured here. Illustrations of "Ardi" may be viewed in a scientific paper.
The skull of the world's oldest known skeleton of a human ancestor—4.4-million-year-old "Ardi," after her species Ardipithecus ramidus—is shown in a digital reconstruction.
According to at least one scientist, Ardi's apparent ability to walk on two legs may have been related to a revolutionary development in human evolution: monogamous sex.
Image courtesy Science/AAAS