Columbia subject headings:
Cruelty--Moral and ethical aspects.
History, Modern--20th century--Philosophy.
Human ecology.
Philosophy, Modern--20th century.
Survival.
Twentieth century.
Harvard subject headings:
Civilization, Modern--20th century
Cruelty--Moral and ethical aspects.
History, Modern--20th century--Philosophy.
Human ecology
Philosophy, Modern--20th century.
Survival
Twentieth century
Princeton subject headings:
Cruelty--Moral and ethical aspects.
History, Modern--20th century--Philosophy.
Human ecology.
Philosophy, Modern--20th century.
Survival.
Twentieth century.