Persons whose contributions are discussed include Sir Thomas Browne, Sir Francis Bacon, Carl Linnaeus, Benoît de Maillet, the Comte de Buffon, Erasmus Darwin, Louis Agassiz, Jean-Baptiste Lamarck, James Hutton, William Smith, Georges Cuvier, Étienne Geoffroy Saint-Hilaire, Sir Charles Lyell, Thomas Robert Malthus, William Wells, Patrick Matthew, Karl von Baer, Robert Chambers, Thomas Henry Huxley, Sir John Richardson, Alexander Humboldt, Gregor Mendel, Hugo De Vries, W. L. Johannsen, Lambert Quételet, and Alfred Russel Wallace. Critics discussed include Fleeming Jenkin, A.W. Bennett, Lord Kelvin, and Adam Sedgwick, both a mentor and a critic.