Original: By that time the ideas were widespread in progressive social circles, 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.
Simplified: By that time the ideas were widespread in progressive social circles. One supporter was the novelist Harriet Martineau whose circle of acquaintances included Charles Darwin. The ideas of Malthus were a significant influence on the inception of Darwin's theory.