Columbia subject headings:
Darwin, Charles, 1809-1882.
Freud, Sigmund, 1856-1939.
Human beings.
Marx, Karl, 1818-1883.
Harvard subject headings:
Darwin, Charles, 1809-1882
Freud, Sigmund, 1856-1939
Human beings.
Marx, Karl, 1818-1883
Princeton subject headings:
Darwin, Charles, 1809-1882.
Freud, Sigmund, 1856-1939.
Human beings.
Marx, Karl, 1818-1883.