Original sentence: One proponent of Malthusianism was the novelist Harriet Martineau whose circle of acquaintances included Charles Darwin, and the ideas of Malthus were a significant influence on the inception of Darwin's theory of evolution
Edited sentence: Malthus' ideas were widespread in progressive social circles in the latter 19th century, one proponent being the novelist Harriet Martineau whose circle of acquaintances included Charles Darwin, and the ideas of Malthus were a significant influence on the inception of Darwin's theory of evolution