To explain how animal diversity formed, some medieval scholars believed that Creation was the result of emanations of a divine substance, continuously flowing from Him. As the flow moves away from God, its divinity decreases; some animals are, therefore, less perfect, and this results in diversity. In man, nothing in the life of an individual is chance, but in plants and animals, Providence is responsible only for the survival of the diversity, whereas chance controls the fate of each individual. Some medieval scholars argued that additional worlds exist; others claimed that the universe consists of an Underworld of minerals, plants, animals and man, a Middle world of stars, and an Upper world of angels, beyond which is God. Angels move the stars and thereby influence creatures (and biodiversity) of the Underworld. There was not much active classification of biodiversity during medieval times. Some speculated that biodiversity was first formed by uncontrolled spontaneous generation; later, God complemented this early phase by miraculously creating additional animals that perpetuate by sexual generation. In each such animal, generation derives both from the male parent and from heavenly bodies, each of which is alive and has a soul. Astrology thus explains both life and diversity. In the Western Roman Empire, Aristotle’s views of biology waned from memory. Prevailing ideas were of a man in the centre of a world, which had been created to serve him. Early Catholic scholars classified animal diversity into eight major groups, thereby reflecting Roman classification, integrated with religious views. Also, a tendency to form natural groups mingled with a tendency to classify by habitat. Scholars labelled as vermin those animals created by spontaneous generation, and classified them by their source: whether generated in the air (spiders), water (leeches), earth (scorpions, slugs), leaves (silkworms) or flesh (tapeworms, lice). An Aquatic group included everything from crabs to whales; snakes received fantastic descriptions. The etymological meaning of Latin names was strongly emphasized, and it too was often fanciful. Bird names had become established as those of the present day by the ninth century, suggesting a good acquaintance with bird diversity. Plant classification consisted of eight major groups. In the Trees group, first came those representing heroic prestige, then trees with juicy fruits, trees with edible nuts, and finally trees in which wood was important. In the medieval approach to biodiversity, the order was very different from our order. Medieval Christians saw in nature a book of moral lessons to enhance belief in Christianity. Physiologus was a treatise that applied animal lore to Christian indoctrination. In it, animal realities were not relevant beyond symbolizing religious values. Bees represent chastity, whales the devil and so on. In the thirteenth-fourteenth centuries, Physiologus developed into the Bestiary, in which accompanying illustrations, as a visual language for the illiterate, were not highly realistic, reflecting a poor knowledge of nature. Hildegard von Bingen’s medicinal text indirectly reveals the place of animal lore in medieval beliefs: In fishes, males partake in fertilization only sometimes, by spitting matter from their mouth over the roe; sometimes, females spit “seeds” from their mouth. Whales heave onto land where males discharge milt over eggs, which females then discharge. Some animal kinds are hybrids between fish and serpents, others are hybrids between mammals and birds, and adolescent girls attract unicorns and vermin bubbles from the soil. Hildegard may have described “helping”: adolescents who remain in association with their parents, to help them raise subsequent broods. Frederick II wrote on bird diversity, classification, food, flight, roosting, migration, mating and functional morphology. He classified birds into waterfowl, land birds and neutral birds. Being a falconer, he offered accurate descriptions of the raptors, dividing them by feeding mode. He generalized as to who migrates and when, in view of flight ability, site, climate and feeding habits; and which returning birds occupy the same nests for many years. Resident birds are polygamous and males do not assist females in nest building, egg incubating or feeding, whereas migratory males assist in brooding and raising young. Migrators nest early in the season, so their young would be strong enough to migrate, whereas resident birds nest later. Large birds lay few eggs, small birds many. Newly hatched chicks feed for themselves and follow their parent; fledglings have their parents feed them, and these include the raptors, who nest in lofty places. Hatched featherless high above ground, the young would fall to their death if they were to leave their nest. After the fledglings can fly and hunt, the parents drive them away to fare for themselves. Frederick’s broad scope of natural history, orderly manner of presentation and reasonable generalizations mark the birth of ornithology. During the High Medieval Europe began commenting on Aristotle’s texts on biodiversity and reproduction. To put order into biodiversity, Albert the Great classified animals by a mixture of morphology, habitat, movement, senses, teaching and learning abilities. He also ranked groups on a scale of perfection: Man, Savage, Monkeys, Furry Quadrupeds, Birds, Aquatic Animals, Serpents and Relatives and Vermin. He emphasized the gap between man, who is perfect, and savages, who speak like man but not rationally, and who do not create art. Monkeys learn, but merely to imitate. Aquatic animals have limited learning ability, lack fine senses and are sluggish; the octopus is inferior to fish because it grows by radial symmetry, which is imperfect. Reptiles are imperfect, as many lack perfect organs for motion: their legs are often small or absent, and some creep on their bellies. Vermin (insects) cannot learn because they cannot distinguish words. Albert rejected beliefs in many mythical animals and in many strange ideas about animal behaviours. His treatise suggests that medieval naturalists were well aware of genus-level diversity in their surroundings. Names of European mammals have remained stable, at least since medieval times. Albert believed that spontaneous generation occurs among terrestrial invertebrates, whereas sexual generation prevails in vertebrates. Semen contains one temporary substance responsible for individual change throughout a lifetime, and another substance that is eternal, unalterable and which is relevant to the individual’s group. By receiving the form of a group, an individual participates in divine permanence and is part of the divine order. The spirit of the embryo forms inside the parents’ testicles. The soul forms only when the embryonic body has been organized, as it requires a body distinguished in shape from that of other animals. It has (in humans) vegetative, sensitive and rational components, and a formative power generates the first two; the Prime Intellect directly inserts the rational soul into the embryo. Matter is pure potentiality, with new embryonic parts developing by a gradual shift, from potentiality to actuality (“epigenesis”). Celestial bodies influence life—Albert believed in astrology, and he explained stillbirths and monstrous animal births by star movements. Throughout the Medieval, intellectuals, including Albert, believed that life on Earth is a microcosm within the macrocosm, and that humans follow patterns and cycles analogous to those of the world. Albert’s text was, to some extent, also an applied zoology. Early medieval law prohibited cadaver dissection. Knowledge of human anatomy narrowed to ancient texts and to dissected animals as human surrogates. Later in the medieval, cadaver dissection became essential for improving knowledge of human anatomy among medical students, increasing awareness of epidemics, improving forensic autopsy and enabling evisceration. Eventually, the church permitted cadaver dissection. Medieval anatomists viewed the human body as composed of three compartments. The abdomen contains the nourishing digestive viscera, which, under the control of the liver, transmits the natural soul through veins. The thorax contains the breathing lungs, supervised by the heart that transmits the spiritual soul through the arteries. The skull is controlled by the brain, which conveys the “animate” part of the soul through nerves. Medieval physicians had difficulty distancing themselves from ancient texts, even when their observations were different. They described the human uterus as having two horns, as in farmyard mammals and that it divides into seven cavities: warmer cavities for male foetuses, colder ones for female foetuses and one for hermaphrodites. They thereby tended to describe texts based on animal anatomy, not from what they actually observed, in their human dissections. Teaching presents comprehensive views of a discipline and its mainstream ideas. Fourteenth-century medieval lectures attempted to rationalize religious faith by integrating the Creation text with knowledge: the Biblical “Let there be light” lecture discusses light and perspective, and so on. Growth and generation are unique to life. Plants are generated by seeds that grow by attracting nutrients and converting them into tissues and another generation of seeds. Animals reproduce by eggs, which supply nutrition; they need an active male sperm to cooperate with a passive female one. Spontaneous generation also occurs, with different matter producing different types of creatures and thus increasing biodiversity. Environmental disturbances, combined with the distorted celestial influences, give rise to monsters. God’s plan of Creation, as revealed by animal diversity, is a process from imperfect to perfect, from plant to animal and from animal to man. Within each of these links, an inner chain of perfection also occurs. Living creatures exist as an interdependent community that maintains a balance, with each member performing its role. God had created the world as a giant clock, and His presence ensures both that there is a clock and that it keeps running.