"Evolution in Modern Thought" was a collaborative effort between several notable scientists and thinkers of the time, including Ernst Haeckel, J. Arthur Thomson, August Weismann, and others. Ernst Haeckel was a German biologist, philosopher, and artist who lived from 1834 to 1919. He was a prominent advocate for Darwin's theory of evolution and was known for his work on the classification of living organisms. Haeckel was also an influential proponent of the idea of recapitulation, which suggested that the development of an organism mirrored the evolutionary history of its ancestors. August Weismann was a German biologist who lived from 1834 to 1914. He was known for his work on the inheritance of acquired characteristics and his experiments on the transmission of genetic traits. Weismann was also an important contributor to the modern synthesis of evolutionary theory. Together, Haeckel, Thomson, Weismann, and the other authors of "Evolution in Modern Thought" played an important role in shaping our understanding of evolutionary theory and its impact on modern scientific thinking.