The Origin of Species. (1869. Last (sixth) edition. Reprinted 1901.) By Charles Darwin.
The Descent of Man. (1871. Second edition, 1874. Reprinted 1906.) By Charles Darwin.
These classics now cost only half-a-crown apiece.
The beginner should read The Descent of Man first, I think. Some of the earlier chapters are of the utmost eugenic value, and would be found immensely interesting by modern lecturers on decadence, and the like.
Darwinism To-day. (1907.) By Vernon L. Kellogg.
An interesting and scholarly recent criticism, containing much matter strictly relevant to eugenics.
The Evolution of Sex. (The Contemporary Science Series. Revised edition, 1901. Originally published in 1899.) By Patrick Geddes and J. Arthur Thomson.
A famous book, yet to be discovered by most “authorities” on the Woman Question.
A History of Matrimonial Institutions. (1904.) By G. E. Howard.
This is a three-volume treatise, extremely comprehensive, and especially valuable as a guide to the literature of the subject. Only the professional student can be expected to read it from cover to cover, but it is invaluable for purposes of reference.