In 1871 Ernst Haeckel, in response to Darwin's 'The Descent of Man', elaborated on the theory and drew this family tree. His enthusiasm led him to improperly include the platypus and kangaroo as ancestors of man. But in charting the emergence of the human species from a unicellular organism to amphibian (1-15) stages to those of primitive mammal, monkey and ape man (22-24), he was essentially correct.