made upon all of his predecessors. The Dutch historian of science Eduard Jan Dijksterhuis wrote that Aristotle and his predecessors showed the difficulty of science by "proceed[ing] so readily to frame a theory of such a general character" on limited evidence from their senses. In 1985, the biologist Peter Medawar could still state in "pure seventeenth century" tones that Aristotle had assembled "a strange and generally speaking rather tiresome farrago of hearsay, imperfect observation, wishful thinking and credulity amounting to downright gullibility". By the start of the 21st century, however, Aristotle was taken more seriously: Kukkonen noted that "In the best 20th-century scholarship Aristotle comes alive as a thinker wrestling with the full weight of the Greek philosophical tradition." Alasdair MacIntyre has attempted to reform what he calls the Aristotelian tradition in a way that is anti-elitist and capable of disputing the claims of both liberals and Nietzscheans. Kukkonen observed, too, that "that most enduring of romantic images, Aristotle tutoring the future conqueror Alexander" remained current, as in the 2004 film Alexander, while the "firm rules" of Aristotle's theory of drama have ensured a role for the Poetics in Hollywood. Biologists continue to be interested in Aristotle's thinking. Armand Marie Leroi has reconstructed Aristotle's biology, while Niko Tinbergen's four questions, based on Aristotle's four causes, are used to analyse animal behaviour; they examine function, phylogeny, mechanism, and ontogeny. Surviving works Corpus Aristotelicum The works of Aristotle that have survived from antiquity through medieval manuscript transmission are collected in the Corpus Aristotelicum. These texts, as opposed to Aristotle's lost works, are technical philosophical treatises from within Aristotle's school. Reference to them is made according to the organization of Immanuel Bekker's Royal Prussian Academy edition (Aristotelis Opera edidit Academia Regia Borussica, Berlin, 1831–1870), which in turn is based on ancient classifications of these works. Loss and preservation Aristotle wrote his works on papyrus scrolls, the common writing medium of that era. His writings are divisible into two groups: the "exoteric", intended for the public, and the "esoteric", for use within the Lyceum school. Aristotle's "lost" works stray considerably in characterization from the surviving Aristotelian corpus. Whereas the lost works appear to have been originally written with a view to subsequent publication, the surviving works mostly resemble lecture notes not intended for publication. Cicero's description of Aristotle's literary style as "a river of gold" must have applied to the published works, not the