Originally published in 1914, this book studies the causes that lead to the appearance of males and females in a number of species, including humans. Doncaster uses simple language to appeal to a non-specialist audience, and the text is illustrated with a number of plates illustrating the differences between the sexes in insects, birds and mammals.

Originally published in 1914, this book studies the causes that lead to the appearance of males and females in a number of species.