[6] "The Growth of the Brain" by H.H. Donaldson, Professor of Neurology
in the University of Chicago.

[7] "The Mind of Primitive Man" by Franz Boas.

[8] "The Antiquity of Man" by Arthur Keith, M.D., LL.D., F.R.C.S.,
F.R.S.

[9] "Ancient Hunters" by W.J. Sollas, D.De., LL.D., Professor of Geology
and Palæontology in the University of Oxford.

[10] "Anthropology" by R.R. Marett.

[11] "The Antiquity of Man" by Arthur Keith, M.D.

[12] "Initiative in Evolution" by Walter Kidd, M.D., F.R.S.E.

[13] "The Antiquity of Man" by Arthur Keith, M.D.

[14] "The Growth of the Brain" by H.H. Donaldson.

[15] "Social Environment and Moral Progress" by Alfred Russell Wallace,
O.M., D.C.L., Oxon.

[16] "The Varieties of Human Speech" by Edward Sapier, in Smithsonian
Institute Report for 1912.

[17] "730 Sechuana Proverbs" by Solomon T. Plaatje.