History of Animals

Written in the fourth century BCE by the Greek philosopher Aristotle, History of Animals is one of the earliest and most ambitious works of biological investigation to survive from antiquity. Across 10 books, Aristotle establishes a systematic framework for classifying the animal kingdom and provides detailed observations on anatomy, reproduction, behavior, diet, migration, disease, and ecology, drawing on his own dissections, the reports of fishermen, hunters, and herdsmen, and the writings of earlier natural philosophers.

Aristotle opens the treatise by laying out principles for comparing and classifying animals. He distinguishes between simple body parts, such as flesh and bone, and compound parts, such as the hand or head. Animals of the same class share the same parts but differ in degree, while animals of different classes share parts only by analogy: A bone corresponds to a spine, a nail to a hoof, a feather to a scale. He classifies animals by habitat, diet, temperament, and social organization. He divides animals into sanguineous (those with blood) and exsanguineous (those without), and into viviparous (producing live young), oviparous (producing eggs), and vermiparous (producing larvae). He asserts that man alone possesses reasoning and recollection, though many animals share memory and the capacity for instruction.

Having established this framework, Aristotle introduces the human body as the anatomical standard against which all other animals are measured, since it is the form best known to everyone. He surveys the external parts in systematic order, from the cranium and its sutures to the face, eyes, ears, nose, mouth, neck, thorax, belly, genitalia, arms, and legs. He then describes the internal organs: the brain (the largest and moistest in man relative to body size, cold to the touch, and containing no blood), the trachea and esophagus, the heart (with three cavities, inclined to the left in man), the lungs, the diaphragm, the liver and spleen, the kidneys, and the bladder.

The second book extends this anatomical survey to other animal classes. Aristotle compares viviparous quadrupeds to humans, noting that the elephant uses its trunk as a hand and that the lion's neck contains a single bone without vertebrae. He catalogues differences in hooves, horns, teeth, and bodily coverings such as hair, scales, and feathers. He gives extended descriptions of the ape, whose anatomy combines human and quadruped features, and the chameleon, whose eyes turn independently and whose skin changes color. He also surveys the general anatomy of birds and fish, observing that the dolphin, though aquatic, is viviparous and suckles its young.

The third book addresses the organs of generation and the vascular system. Aristotle describes the testicles and the uterus, noting that cotyledons, or placental attachments, appear in the pregnant uterus of horned animals. He presents and corrects earlier accounts of the veins by the physician Syennesis of Cyprus, the natural philosopher Diogenes of Apollonia, and the medical writer Polybus, then offers his own description of two principal veins originating in the heart: the great vein and the aorta. The remainder of the book surveys the body's homogeneous parts, including sinews, bones, cartilage, hair, skin, flesh, fat, blood, milk, and semen.

The fourth book turns to exsanguineous animals. Aristotle describes the cephalopods (including the polypus, sepia, and teuthis), the crustaceans (lobsters, prawns, crabs), the testacea, or shelled animals (bivalves, turbinated shells, and the echinus, or sea urchin), the ascidians, and insects. The book concludes with a comparative treatment of the senses, voice, sleep, and sex differences across all animal classes.

Books Five and Six form a continuous treatment of reproduction. Aristotle works methodically through testacea, crustaceans, cephalopods, insects, fish, birds, and quadrupeds. He describes how butterflies develop from caterpillars through a chrysalis stage and how the ephemeral insect of the river Hypanis emerges from a capsule and dies within a single day. He provides an extended account of bees, presenting competing theories about their reproduction and detailing the construction of hexagonal wax cells, the roles of workers, rulers, and drones, and the collection of honey. For birds, he traces the development of the chick within the egg day by day, from the first palpitating red spot of the heart to the hatching of the downy chick. He notes that barren eggs can become fertile if a hen mates with a new male before the egg's color shifts from yellow to white, producing young of the new male's nature. For fish, he distinguishes oviparous species from the ovoviviparous selache, or cartilaginous fish, and discusses the spontaneous generation of certain fry from mud and foam. He asserts that eels originate not from intercourse or eggs but spontaneously from moist soil.

The seventh book focuses on human reproduction: puberty, menstruation, conception, fetal development, and parturition. Aristotle states that the male fetus, if excluded within 40 days and placed in cold water, appears about the size of a large ant with all its parts visible and disproportionately large eyes. He notes that gestation varies from 7 to 11 months and that infants born before 7 months never survive.

The eighth book shifts to animal behavior and ecology. Aristotle surveys diets across all classes, describes seasonal migrations, catalogs hibernation patterns, and discusses diseases affecting domestic and wild animals. He observes the influence of locality and climate, noting that animals of the same species differ in size, temperament, and fertility depending on their environment.

The ninth book provides an extended study of animal relationships and intelligence. Aristotle catalogs enmities and friendships among species, traces the prudent behavior of deer, bears, and ichneumons (small carnivorous mammals known for fighting serpents), and describes the elaborate social organization of bees and wasps. He discusses the gentle character of the dolphin, which has been observed supporting its dead young on its back, and the intelligence of the elephant, which he calls the most tame and gentle of wild animals. The book closes with observations on the effects of castration and seasonal changes in animal coloring and voice.

The tenth book, which scholars acknowledge is erroneously attributed to Aristotle, presents a medical treatise on human barrenness. It examines conditions of the uterus, menstrual regularity, and the compatibility of partners, arguing that conception fails when male and female do not emit their seminal fluids simultaneously. It also discusses the condition called myle, an amorphous mass of flesh that forms in the uterus when the reproductive substance of only one sex is present, persisting for years without causing pain.