Early Greek philosophers discussed what matter is, and how man and animals came about. Some suggested that Man first developed within an egg case, from which he hatched and emerged onto land. Others claimed that animals originated from primordial moisture. Another theory proposed that creatures formed under a cosmic cycle of eternal change, growth, and decay. At first, only limbs formed, later they came together; but only creatures with homogeneous limbs, as found in the animals of today, have survived. Others suggested that the world consists of eternal, invisibly minute atoms, moving about in an infinite void and forming perishable combinations. Animals are classified into those with blood, versus those without red blood. Plato believed that a world of ideas exists beyond this real world, which compares to a huge well-organized animal, and that entities of this world are mere shadows of eternal concepts. In our world, each element consists of geometrically unique atoms; and some entities are included within each other. To classify and define them, one should start with the broadest entity, and narrow the possibilities by dividing it in two, by the presence/absence of a single trait (dichotomy). We thus obtain a hierarchy, of small groups in relation to more inclusive ones. Aristotle believed that entities of this world are not mere shadows of eternal concepts. He claimed that we can understand the basic principles of the world by sensing it, by reasoning, or by generalizing. The universe is timeless. It consists of a series of globes, one inside the other with an unmovable Earth at the centre, consisting of the four elements and four qualities. Furthermore, it consists of matter and form, and movement expresses the dominance of form over matter. Earth, the “underworld”, forever changes, by growing, generating, and perishing. The heavens, from the moon and beyond, form the “upper world”: a series of constantly rotating transparent spheres, one surrounding the other and containing the unchanging stars, which consist of a fifth, never-changing element. Above these is a starless heaven in which there is no matter, only form. Nothing exists beyond it. The world is thus limited, finite, and closed. All spheres touch each other, and they transmit movement of the uppermost sphere, down to Earth. The unchanging eternal, constantly repeating movement of the heavens is thus responsible for everything that exists and changes on Earth. Aristotle criticized Plato’s abstract classification by single trait dichotomies, since his method might split up natural groups and, on the other hand, create meaningless ones. Our world consists of real groups and real sub-groups, so a correct classification of animals should begin by applying straightforward intuition and clustering of animals into large, generally accepted groups, that we clearly define. Within each intuitive group, sub-groups usually differ merely by quantifiable traits, of more and of less. Species are what they are because they belong to groups that are more inclusive. In his terminology of grouping, Aristotle used the terms Genos to describe any group above species level and Eidos to represent the subgroup of any genos. We should classify animals by syllogisms: If A belongs to B, and B belongs to C, then A necessarily belongs to C. The outcome is a formal definition of what a kind is. We need not state all features of a kind, just its position in the structure of kinds, with a definition that separates it from other kinds. Comprehensive intuitive classification and subsequent divisions are thus counterparts of the intrinsic order in animal diversity. Aristotle developed a rather complete, full-blown classification of the animal world. All animals have a heart and a digestive tract. Some animals have no blood (our invertebrates), others have blood (vertebrates). Invertebrates divide into four major groups: those with soft bodies, soft shells, hard shells, and terrestrial invertebrates. Two minor groups, sea anemones and sponges, link animals to plants. Aquatic vertebrates are all fishes, but sharks and rays differ from bony fishes, and so do dolphins and whales. Among birds, Aristotle appears to have recognized six subgroups. Among terrestrial quadrupeds, some lay eggs (our reptiles and amphibians), and others bear live young (mammals, including man). Most mythological animals are fantasies. Aristotle thus set up a complete taxonomic system of very many animal groups and created a comprehensive and broadly correct classification. He erred in placing sea urchins and sea squirts with snails and bivalves, starfishes close to sea anemones, and whales and dolphins with bony fish and sharks. For a first-ever attempt at classifying the entire animal world, his classification broadly lives up to the expectations of his theory and method. The number Four, which had a special significance in the ancient world, may perhaps have inadvertently seeped into parts of his animal classification. Aristotle thought that earthly mortals imitate heavenly immortals by generation. The diverse generative abilities of animals form a ladder, in which terrestrial mammals are at the top as they nourish their embryos via placentas and, after their birth, they suckle their babies. Birds come next because they lay two-coloured eggs that are perfect, in that they have a hard shell. They feed their offspring, but only for a short time. Reptiles lay imperfect eggs in that they have a soft shell; they do not feed their hatchlings. Fishes and cuttlefish lay imperfect eggs in that they lack a shell; hatchlings resemble adults. Flies (and other insects) lay imperfect eggs in that they lack a shell; furthermore, the hatchlings differ considerably from adults. Snails, bivalves and sea urchins generate spontaneously from rotting matter, their diversity requiring species-specific temperatures. Spontaneously generated species lack the continuum of generations, produced in sexual animals. Eggs need heat to develop into embryos. This heat may come from the sun, but many eggs need also the warmth of their brooding parent bird. Animals consist of matter and form. To explain generation, namely life forming from nothing, Aristotle distinguished between potentiality (ability) and actuality. Development is the realization of a potential form. The male, who activates matter and bestows future form on the offspring, is more divine than the female, who merely contributes matter. The soul makes matter and forms into a living entity by activating nutrition, growth, reproduction, movement, sensation, and understanding. Life occurs at three levels: nutrition, growth and generation, common to plants, animals and humans; movement, sensing, and response to stimuli, restricted to animals and man; and rational abilities, restricted to man. The embryo sequentially actualizes the corresponding vegetative, sensitive, and rational souls. The soul acts via the spirit. During embryo formation, the character of a higher taxonomic group forms before that of a lower group: the embryo forms characters that make it an animal, not a plant, before characters that make it a man, not a horse. The embryo’s sex depends on the father’s heat. Maleness is a dominant character, beneath which femininity is a hidden potential. If the male character is strong, the offspring will be male, if weak, female. Environmental factors also determine sex. Aristotle also believed in spontaneous generation. Coming slightly after Aristotle, Theophrastus proposed a general classification of plant diversity into trees, shrubs, under-shrubs and herbs. He believed that some plants change their kind as they grow, and he believed in spontaneous generation. In emphasizing applied aspects, he described the many different uses of wood and resins of different trees. Epicurus believed that the world consists of eternal, unchanging atoms, and of void. The world is unlimited in size, with an unlimited number of atoms, and an unlimited amount of void. All things are conglomerations of atoms, all events are atom collisions, that result in ever-changing conglomerations. Our present world is a temporary agglomeration that eventually will fall apart. Atomic collisions may form organs and, if an organ can fulfil a function, then function sets in. Form, however, was created before function. The soul too consists of atoms and void, and it disintegrates when the body dies. In Alexandria, the Greek rulers built a museum—a storehouse of texts and a school of philosophy, the first-ever state-supported institute of research. In Rome, Pliny’s military and administrative experience may have shaped some of his interpretations of animal behaviour. Bee’s daily life resembles the daily routine in a military camp. Moral aspects in the behaviour of two animals reflect traditional, unwritten codes of Roman social norms. Elephants think rationally, understand human language, obey orders, and remember duties. They are honest, wise and just, have reverence for the sun, moon and their king, and conduct purification rituals. Being modest, they mate only in private; adultery is unknown. Good-tempered, peaceful and gentle, they enjoy marks of honour, yet hate shame and disgrace. Lions are noble and merciful. When enraged they turn their fury on men rather than women and attack children only when extremely hungry. Otherwise, they are enraged only at the disrespect of those who dare challenge them. When pursuing they charge by leaps, when retreating they do so in slow dignity. All this suggests that Roman values and customs are part of the world’s grand order of nature. Pliny further wrote that the universe is an eternal being, the Sun being its soul and mind. Earth, at its centre, consists of four elements. Heavens belong to the gods but Earth, with its nature, belongs to men. Nature creates everything, including plants and animals, solely for the benefit of man, to exploit it. Nature is rational, so well-ordered that even tiny animals display bodily perfection; and so powerful that it can change animals, from one kind to another. Animal remedies are part of this grand Nature-for-Man plan. Pliny classified medicines by their animal origin: remedies from Man, farm animals, wild animals, and plants. Pliny classified animals into those on land, in the water, in the air, and insects, thereby mixing habitat and natural groups, and somewhat reflecting the four elements. In his terrestrial animals, there was not much order, beyond clustering all domestic kinds in one sequence. Among aquatic ones he described mammals, then fishes, and then invertebrates, the latter in increasing order of their armour: without shells, crusty, and hard shells. He believed that animals on land have aquatic versions: certain aquatic animals resemble sheep, horses, and bulls. Among aerial animals, Pliny clustered birds of augury. His “plumage birds”, included the peacock, sacred to the goddess Juno; the farmyard cock, who tells the future; and the goose, sacred to Romans. Some insects dwell on the ground but others fly (through fire). Bees, alone among insects, serve man with their honey and wax. Like man, they toil, construct hives, and have a government with collective leaders. Drones, lacking stings, serve the true bees, who order them about and drive them out to work. Hatched offspring resemble maggots but the king has wings, from the start; a retinue of peers escorts him everywhere. Pliny’s animal world contained several fabulous animals (phoenix, unicorn, and sphinx). Dioscorides, a Roman physician, wrote of plants and medications, in a medicinal order: aromatic oils and plants that produce them, animals and agricultural plants from which medications are prepared, roots, seeds and various plants, and grapevine. Galen was a Roman physician. As law prohibited cadaver dissection, he dissected animals, assuming they resembled humans. He mastered the approach of controlled experiments, to test functions of an organ. The body operates through a natural soul (liver), for appetite and pleasure; a vital soul (heart) that governs emotions; and a rational soul (brain) that governs reason, memory, and motion. These souls have different vessels: veins, arteries, and nerves. Disease results from an imbalance of the four body humours, each associated with qualities of one of the four elements. Concerning reproduction, semen derives from the body’s humours, drawn from all organs to the testicles, complete and with souls. Females produce imperfect semen, which has generation powers upon mixing with male semen, during copulation; a fleshy embryo develops. During intercourse, if male sperm falls on the right side, the baby will be male; on the left side—female. If male semen is more abundant, the child will look like the father; if the mother’s is, then like the mother. If in the semen, one humour is more abundant than the others are, the child will follow that humour and be sanguine, choleric, phlegmatic or melancholic; and not like its parents.