Passage: The pre-Socratic philosophers asked many questions about life but produced little systematic knowledge of specifically biological interest—though the attempts of the atomists to explain life in purely physical terms would recur periodically through the history of biology. However, the medical theories of Hippocrates and his followers, especially humorism, had a lasting impact.The philosopher Aristotle was the most influential scholar of the living world from classical antiquity. Though his early work in natural philosophy was speculative, Aristotle's later biological writings were more empirical, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, which he devoted considerable attention to categorizing. In all, Aristotle classified 540 animal species, and dissected at least 50. He believed that intellectual purposes, formal causes, guided all natural processes.Aristotle, and nearly all Western scholars after him until the 18th century, believed that creatures were arranged in a graded scale of perfection rising from plants on up to humans: the scala naturae or Great Chain of Being. Aristotle's successor at the Lyceum, Theophrastus, wrote a series of books on botany—the History of Plants—which survived as the most important contribution of antiquity to botany, even into the Middle Ages. Many of Theophrastus' names survive into modern times, such as carpos for fruit, and pericarpion for seed vessel. Dioscorides wrote a pioneering and encyclopaedic pharmacopoeia, De Materia Medica, incorporating descriptions of some 600 plants and their uses in medicine. Pliny the Elder, in his Natural History, assembled a similarly encyclopaedic account of things in nature, including accounts of many plants and animals.A few scholars in the Hellenistic period under the Ptolemies—particularly Herophilus of Chalcedon and Erasistratus of Chios—amended Aristotle's physiological work, even performing...

Question: Claidius Galen became an expert known widely in what field?
medicine and anatomy