Ouspensky, P.D.
Hodder and Stoughton, 1957
Buku Teks
Pilbeam, David, author
Funk and Wangnalls, 1970
Buku Teks
edited by Louise B. Young
Oxford University Press, 1970
Buku Teks
edited by M. F. Ashley Montagu
Oxford University Press, 1962
Buku Teks
Dobzhansky, Theodosius, author
John Wiley, 1955
Buku Teks