Alcmaeon also was the first to dwell on the internal causes of illnesses. It was he who first suggested that health was a state of equilibrium between opposing humors and that illnesses were because of problems in environment, nutrition and lifestyle. A book titled "On Nature" is attributed to him, though the original title may be different, as Alexandrian writers were known to have ascribed the title "On Nature" to a wide variety of works. According to Favorinus's account, Alcmaeon has been the first who wrote such a treatise on natural philosophy (), however this has been disputed, because Anaximander wrote before Alcmaeon. Accounts which attribute an Alcmaeon of Croton to be the first to write animal fables, may be a reference to a poet with the same name. He also wrote several other medical and philosophical works, of which nothing but the titles and a few fragments have been preserved by Stobaeus, Plutarch, and Galen.