Aristotle: Natural History and Zoology

Aristotle: Natural History and Zoology

It is not clear when Aristotle wrote his zoology, or how much of his natural history was his own work. This is unfortunate, for it might help us to interpret his philosophy if we knew whether he began theorizing in biology before or after his main philosophical formulations, and how many zoological specimens he himself collected and identified. Some believe that he began in youth, and that his theory of potentiality was directed originally at the problem of growth. Others (especially Jaeger) hold that his interest in factual research came late in life and that he turned to biology after founding the Lyceum. Most probably, however, it was in middle life, in the years 344–342 b.c., when he was living on Lesbos with Theophrastus; many of his data are reported from places in that area. This would imply that he wrote the zoology with his philosophical framework already established, and on the whole the internal evidence of the treatises bears this out. It follows that in order to understand his zoological theory, we must keep his philosophy in mind. Yet it may also be true that in thinking out his philosophy, he was conscious of biological problems in a general way.

The zoological treatises must represent many years’ work, for they make up a fourth of the whole corpus, and both data and discussion are concisely presented. They owe little to Herodotus, Ctesias, Xenophon, or other extant literature; their possible debs to Democritus cannot be assessed, however, because his three zoological books are lost. Comparing the quality of Aristotle’s data with previous writings, we must conclude that he sifted and rejected a great deal; even by modern standards of natural history his reports are cautious. The chief collection of data is the Historia animalium. Out of 560 species mentioned in all his zoology, 400 appear only in this work and only five are not included. The treatises, as we now have them, form a course of instruction in which the Historia is referred to as the descriptive textbook, intended to be studied first and then kept at hand. Internal evidence suggests, however, that it was in fact written after the others, and that most of it was not written by Aristotle himself. This implies that he wrote the theoretical treatises before the main collection of data. Not that the treatises lack supporting data, but most of the information was common knowledge, whereas the reports that read like new, firsthand observation are nearly all confined to the later parts of the Historia.

Biological data were normally quoted in cosmological arguments, not least in the Academy. The Academicians’ interest was not so much in the animals for their own sake, but rather in using them as evidence for—and giving them a place within—a rational cosmology. There were two issues: to identify the formal groups of animals, and thus to classify them, and to explain their functioning as part of nature. Plato and Speusippus opposed the materialism of those like Democritus, whose lost books, entitled Causes Concerning Animals, were probably intended to explain biology in terms of atomism. Aristotle would have been familiar with these discussions since his youth, and his writings follow this essentially etiological approach. His earliest zoology is probably in the De partibus animalium, the De incessu animalium, and the Parva naturalia (all of which in their present form show signs of revision and editing), in which he sets out the“causes” of tissues and structures, and of such significant functions as locomotion, respiration, aging, and death. Here the a priori element in his theory appears strongly: for example, right is superior to left, and hence the right-hand side is the natural side to lead off with; organs properly exist in pairs, and hence the spleen (for which he found no function) exists as the partner of the liver. On the other hand, the teleological explanation, which is the main theme of De partibus animalium, is argued in a mature fashion with evidential support. This scientific maturity is even clearer in the next great treatise, De generatione animalium, in which he applies his concepts of form and matter, actuality and potentiality, to the problems of reproduction, inheritance, and growth of such inessential characters as color. On the question of classification he remains tentative and critical, as we would expect of one who rejected Plato’s theory of Forms. He often returns to the problem in both early and late writings, but states no clear position.

His teleology differs from others. He argues it in De partibus I on the same grounds as in Physics B, where he states more of his opponents’ case. He makes it clear that the “natural philosophers” (Empedocles, Anaxagoras, Democritus) were combating a popular teleology which presented the gods as purposive powers intervening in nature, so that “rain falls in order to make the crops grow.” Against it they had argued that the “necessity” of natural causes was sufficient to explain events and that the crops happened to grow because the rain happened to fall, the real cause being the automatic interactions of the hot, the cold, and the other elements. In reply, Plato had posited a world soul and a creative “Demiurge.” Aristotle, however, does not invoke a supernatural agency (for the relation between the cosmos and the Unmoved Mover is different), nor does he present nature as a quasi-conscious entity capable of purpose: his personification of nature “who does nothing in vain” is no more than a rhetorical abbreviation for “each natural substance.” Neither does he posit an extra factor in nature, as modern teleologists posit a conatus that is not reducible to physics.

The directiveness that Aristotle sees in nature is part of the natural interactions, so that the teleological explanation coexists with the causal explanation. But he bases the teleology not primarily on directiveness but on the existence of forms. To explain an organ, he says, we must first grasp the complete animal’s form and functions, what it means to be that animal, its ousia. Our explanation will include both the “necessary” causes and the “end” toward which development tends. This is not the temporal end or a state of equilibrium between phases of activity; indeed, it may never be reached. It is the perfect condition of the whole animal, “for the sake of which” each part develops. Thus, Empedocles was wrong to suppose that the spine is vertebrated because it gets bent: on the contrary, vertebration is necessary to the animal’s functioning, and was contained potentially in the parent’s seed before the embryo’s vertebrae were formed. He was also wrong to think that random necessity could be a primary cause, for it could not produce the general regularity of nature, let alone the absolute regularity of the stars. Necessity in nature is secondary, or, as Aristotle calls it, “hypothetical”: on the hypothesis that an animal is coming into existence, certain materials must interact, but these materials do not of themselves produce the animal any more than bricks produce a house. As the house needs a builder and a plan, the animal needs a soul and a form—factors ignored by the materialists. But whereas builder and plan are separate, soul and form are identical. The final cause of the animal is the actualization of its form, and its primary efficient cause is its soul, which “uses” the necessary movements of the materials. Aristotle’s teleology therefore rests upon his theory of substantial form. The definition of a substance is logically prior to the definition of its parts, and so the final cause is prior to the necessary cause. It is prior temporally as well as logically, for Aristotle believed that the world never began—so that hen has forever preceded egg.

Although he used Plato’s language (“existence is prior to coming-into-existence” and necessity is “the concomitant cause”), Aristotle did not follow Plato in positing an overall teleology or in the dualism that the Timaeus set up between creator and material. The few passages where Aristotle seems to imply that some species exist for the sake of man, or act for the general good as opposed to their own, cannot be meant literally. What he probably meant was a balance of nature, in which species are interdependent. The final cause of each animal is its own complete state, and nothing more. And instead of Plato’s dualism, Aristotle places finality within natural interactions, not as something imposed upon them.

Within sublunary nature there are continual fresh beginnings of movement for which there are no sufficient external causes. They may be stimulated from outside, but the source of the movements in plants and animals is their souls. Only in a general way is the Unmoved Mover the prime cause. As a final and formal cause it presents the perfection that lesser beings desire to imitate. It can therefore be argued, although it is never clearly stated by Aristotle, that nature’s tendency toward actualization and the orexis within souls are ultimately oriented toward the Unmoved Mover’s perfection. As an efficient cause, the Unmoved Mover promotes general growth and decay on earth because it elicits the sun’s movements in the ecliptic, and these movements cause the alternation of summer and winter. These general causes, however, do not bring about the particular starts of motion in nature. Nor, again, are souls regarded as separable entities that inhabit bodies and direct them, as Plato thought and as Aristotle may once have thought but later rejected. In his mature view, found in his biology as well as in the Metaphysics and De anima, the soul (except, possibly, for the intellect) is not an independent substance but is the form of the body. On the other hand, it is not merely a resultant form, as in the “harmonia” theory, which Aristotle refuted; rather, it is both form and source of action. In plants it causes growth and reproduction; in animals it also causes sensation (here he differs from Plato, who thought that plants had sensation); in man the soul has a third faculty, intellect, and this is its only faculty that is not the form of body and could therefore be separable.

The concept of soul as both form and efficient cause may reflect a trace of ancient hylozoism. In Aristotle’s view, finality pervades nature. If there is a cosmos, this implies that the elements not only have simple motions but also combine with modified motions. Both the simple motions and their modifications are hypothetically necessary and are natural. An animal contains many motions, all natural, that by a natural coordination tend toward a specific pattern. Its soul is both the tendency and the pattern. In nonliving substances, which have no soul, the tendency to form complexes is in their nature. Aristotle accepts as his data both the observable materials and the observable forms and species; therefore the movement of nature is simultaneously necessitated and endlike.

According to the Metaphysics, the form toward which animals grow is their species: individual differences arise from matter and consequently are unknowable to science. In Aristotle’s earlier zoology we cannot tell whether he maintains this strict view, but in De generatione animalium his theory of reproduction implies that individuals differ in form to some extent. He does not say so, but repeats the doctrine of De generatione et corruptione that sublunary beings, which cannot achieve eternity as individuals, instead achieve it as species by reproduction. Nevertheless, Aristotle’s discussion is in fact about an individual’s reproduction of another animal “like itself.” He starts from the long-standing controversy about the origin of seed. Do both male and female contribute seed? From what part or parts of the body does it come, and what does it contain? He analyzes the problem in terms of form and matter. The male alone makes seed from his blood; it contains potentially the sensitive soul and the adult form, but actually it contains no bodily parts (here he ridicules preformism and pangenesis). The female contributes only material (the catamenia ), whose form is nutritive soul. When the male’s form has been imposed upon the female material, the somatic part of the seed is sloughed away: all that is transmitted is soul, the source of form and motion. If the fetus develops regularly, the father’s form will be actualized; failing that, the mother’s failing that again, more distant ancestors successively, until eventually the form may be merely that of the species, or even just the genus Animal (that is, a monstrous brith).

This long and careful argument, which is supported by observed evidence, gives a brilliant impression of maturity and originality, and in several points goes beyond the biological arguments that we occasionally find in the philosophical works. Aristotle’s view that the father’s form is reproduced, as distinct from the species, can only mean that some individual differences are formal and apodictic. He also brings to scientific account other differences due to “necessity”—not only monstrous births but differences of coloration, voice, or sharpness of senses. Since he calls them “concomitants” arising from irregularities in the material, he may have regarded them as unpredictable, but they seem to be accountable after the event. He now argues not from the fixity of species but from the reproduction of forms. True, he does not contemplate the obsolescence or alteration of existing species (for he had no paleontology); but he does accept, within limits, the evidence for miscegenation’s resulting in new forms. In fact, the emphasis on species becomes less, while the concept of necessity as hypothetical becomes more important and sophisticated than in the philosophical works, where necessity is either “simple” (axiomatic) or brute (material). The one exception among the biological works is the Historia animalium, from which the teleological explanation is absent. Although a discussion of causes is not to be expected here, nevertheless the account of characters and life histories involves some causal explanation; and it is noteworthy that this explanation is given only in material terms. No doubt this is because the Historia was mainly the work of Aristotle’s successors, among whom Theophrastus ignores the final cause even in his Causes of Plants.

In explaining the “necessary” causes—the interaction of materials—Aristotle does not innovate so much as rationalize theories that were already current. He accepts from Plato’s Timaeus the four elements—fire, air water, and earth—that were common to the medical writers and can be traced back through Empedocles into popular tradition. But the tradition had confused two notions: the cosmic regions of fire, air, water, and earth, and the seasonal powers of hot, cold, wet, and dry. The two sets do not exactly match, as is obvious in the ambiguous reports of Empedocles. Aristotle systematizes them by means of a formula that survived through the Middle Ages, treating fire, air, water, and earth as combinations of hot, cold, wet, and dry: fire is hot plus dry, air is hot plus wet, and so on. In his system hot, cold, wet, and dry are the primitive qualities of matter, but cannot exist in isolation. Fire, air, water, and earth are the simplest separable bodies, and are transformable into each other.

Like his predecessors, Aristotle regards the hot as the chief active power; its characteristic action is pepsis (“concoction”), which transforms food into blood and blood into flesh. By its opposite, the cold, he sometimes means merely the absence of hot, but more often a power in itself. The hot means more than temperature, which he calls “the hot according to touch.” Another sort of hot is that possessed by pine wood, which is not hotter to the touch than other timber but contains more heat and therefore burns better. Animals have an innate heat upon which life depends. Their droppings still contain some of it, which generates flies. While the hot is the soul’s chief agent in bringing about growth, cold is also needed to solidify things. Life the medical writers, Aristotle attaches importance to the due mingling (krasis ) of hot and cold, which does not mean a point on a temperature scale but a mixture of two powers. He follows them in extending this notion to a general “right proportion” (symmetria ) necessary for growth and health.

The other elements—the wet or watery, and the dry or earthy—are needed to provide the fluid and the solid parts of plants and animals. Whether Aristotle really intended a fifth element, pneuma, is debatable. The notion was current, and soon after him it became the chief element for the Pneumatic school of medicine and the Stoics. Aristotle had his own fifth substance in the outer heaven, the aither, and in De generatione animalium he compares it with the bodily pneuma: pneuma is the material of the animal seed, and conveys soul and the generative warmth, which he says is different from other heat. Yet he defines pneuma merely as warmed air, and since warmth has various powers for him, it is probable that he means no more. So he explains spontaneous generation by the presence of a warm soul-source in the materials.

The four elements combine to form the tissues, which Aristotle calls “made of like parts” (as flesh is divisible into flesh); and the tissues form the organs, which are “made of unlike parts” (hand is not divisible into hands). Taking this distinction from Plato, he uses it in finding homologies, but he makes only general statements about the processes. The hot concocts blood into flesh here, fat there, marrow or seed somewhere else; skin, hair, bone, nails, and horn all come from the earthy. He does not explain how. Medical literature of the time contains some practical investigations, such as the action of heat upon blood, and Aristotle occasionally refers to such evidence. In Meteorologica IV he goes further and analyzes the actions of hot and cold into evaporating, emulsifying, dissolving, condensing, and coagulating, and differentiates many types of earthy material. But this is a late work, and may not even be his. It seems, therefore, that in his biology Aristotle is content to take these theories in a general form from current tradition, although he is careful to rationalize them. For example, he will not allow Empedocles to say that spontaneous generation results from rottenness: new life comes not from disintegration but from concoction. The heart—not the brain, as many held—is the center of sensation and of the soul’s motor impulses; as the first part to develop (observed in daily openings of a clutch of eggs), it is the source of the vital heat and innate pnecana. In it the blood is pneumatized and then flows out to nourish the tissues. (The distinction between arteries and veins is post-Aristotelian.) The lungs admit air to replenish the pneuma and to moderate the heat, an excess of which brings on senescence and death. Animals without lungs are cooled by the surrounding air or water: this suffices because they are “less perfect” and therefore cooler; also, their innate store of pneuma is sufficient.

Classification of animals remained a difficulty, and Aristotle suggested a solution by taking an animal’s vital heat as an index of its superiority. Plato had proposed diaeresis (division), in which a major group is progressively divided by differentiae into genera and species. This method, used by Aristotle in his early logic and later by his successors, became the basis of Linnaean systematics. In his zoology, however, Aristotle criticizes it for splitting natural groups. He shows how groupings based on habitat and locomotion, and such characters as horns and rumination, cut across each other, while many animals belong to both sides of a formal division. He also criticizes the emphasis on morphology, which he holds subordinate to function. He prefers to start from the natural genus, as defined by multiple characters, then to arrange it with other types, not in a genus-species hierarchy but in a scala naturae ranging from man through less perfect animals down through plants to lifeless compounds. In this he emphasizes the continuity of nature and the many borderline or overlapping types, such as the seal, the bat, and the testaceans. The degree of vital heat is indicated by method of reproduction, state at birth, respiration, posture, and other signs. But he does not produce an actual scheme, nor does he finally reject genus-species classification. For practical purposes Aristotle discusses the animals by major groups: the “blooded” (i.e., red-blooded)—man, viviparous quadrupeds, oviparous quadrupeds, cetaceans, fishes, birds; and the “bloodless”—mollusks, crustaceans, testaceans, and insects. But he points out that even these groups exclude many types, such as snakes and sponges. In fact, before any classification could succeed, far more information was needed. He may have felt this, for the Historia animalium was begun as a comparative study of characters, arranged under the headings parts, activities, lives, dispositions (i.e., psychology). Major groups were to be compared by “analogy” (as wing to fin), while within a group each structure would vary by “the more and the less” (as wings are longer or shorter).

This project, however, was not carried through; instead, the treatise became a running collection of data. As new information came in and new significant characteristics were distinguished, they were inserted at convenient places, as if into a filing cabinet. Book I gives a program of the characters to be discussed, and by comparing this with the later books, we can see that many of those proposed are never mentioned again while many more new characters come to be recognized, so much so that the whole plan of the treatise is altered. The latest additions, which can be identified in all books from the second onward, consist of dossiers or even complete descriptions of single animals, no doubt awaiting breakdown under appropriate character headings. Thus the work eventually begins to approximate a descriptive zoology, and this is how it has been taken ever since. But in judging Aristotle as a natural historian, we should remember that we are judging him as something that he never set out to be. Although the classificatory intention of the Historia animalium came to nothing, it remained essentially an analysis of differentiae, the ways in which animals “are like to and different from each other,” in the words of the introduction. The data about animals are put there to illustrate characteristic differences, and except in the late and unassimilated additions there is no description of an animal for its own sake. The statements about a given animal are spread through the nine books of the treatise, which is arranged not by animals but by characters. It has repeated signposts helping the reader to find his way among characters, but there are none to help him find animals, and there is no index. Some animals are cited frequently to illustrate but one point-for example, the mole’s blindness: Aristotle obviously examined the mole, for he describes a dissection of its concealed eyes, which is of great interest; but this is all he tells us of the mole. In fact, like all his treatises, the Historia animalium is a theoretical study. It is not so much about animals as about Animal —and the various ways it is differentiated in nature.

Aristotle names about 500 “kinds” of animals. Some of these comprise several varieties, which his reports sometimes distinguish but sometimes confuse. Altogether, between 550 and 600 species can be distinguished, and of these as many as 200 are mentioned in connection with only one character. He includes some thirty from such distant places as Libya, Ethiopia, the Red Sea, and even India. A very few are taken from travelers’ tales, especially from Herodotus and Ctesias, and of these some are fabulous—for example, the flying snake and the martichoras, or manticore (a monster, perhaps derived from a garbled account of the Indian tiger, which became a favorite of the Middle Ages), of which he plainly indicates his suspicion. But most were to be seen in Greece in menageries and shows—certainly the bear, monkeys and apes, elephant, camel, and lion. Aristotle gives much information about all of these, for the very reason that they exhibited interesting differences. Some information is evidently hearsay: for example, he reports that the lion has no cervical vertebrae, which shows that he never examined a dead lion. But his remarks about the lion’s appearance and gait show equally that he observed it in life. He describes the elephant’s leg joints in order to contradict a popular belief that it sleeps standing against a tree.

However, the great majority of Aristotle’s reports concern animals native to Greece, its islands, and the Greek colonies in Asia Minor. It is incorrect to accuse him of showing more interest in exotics than in what was at his own doorstep. If we compare the variety of information given on each animal, we find not only that the nearest animals are the most fully reported but also that he covers most of what was available to him. Among mammals, of which he mentions some eighty, by far the most information is given about the horse, dog, sheep, ox, and pig; next comes a group including the goat, donkey, mule, hare, deer, elephant, bear, camel, seal, and dolphin. Of 180 birds mentioned, the best-reported are the domestic fowl, the pigeons, and the partridge, and there is a good deal on the sparrow, swallow, blackbird, crows, larks, eagles, hawks, quail, and stork. On the other hand, over 100 birds are mentioned only once or twice, as examples of differences in feeding or nesting, and so on. The information on marine animals is especially good, although out of 130 fishes only twenty are cited in connection with more than a very few characters. Among over eighty insects, he gives considerable information about the flies, ants, wasps, and cicadas, and three long, separate discussions of the honeybee; there is a fair amount about the grasshoppers, gadflies, spiders, beetles, and chafers. It is true that he has relatively little on the gnats and mosquitoes, common though they were; but he reports their external structures, reproduction from larvae, feeding, and habitat—and there is, after all, little more that he could know, having no optical apparatus. Aristotle often complains that the smallness of some insects makes it impossible to discern their structures, especially the internal ones. Many features, in all groups of animals, are reported in a generalized form—“all two-winged insects have a proboscis and no rearward sting,” “all fishes except selachians have gill covers”—so that if one is to assess what he knew about a given animal, these general statements have to be broken down and included. In some of them he generalizes further than the facts warrant, through faulty or deficient information.

The tests that Aristotle applies to reports are primarily observational checks, made either on the same type of animal or on “analogous” types. He shows himself well aware of the need for repeated observations, but he has not developed the refined technique of provoked and controlled observations that later (very much later) scientists learned to demand. Where observational checks are not available, he tests by inherent probability—that is, by reference to theory. The accusation that he relies on a priori argument, and not on observation, is not well founded; on the contrary, like most Greek philosophers, with the exception of Plato, he is overready to accept uncontrolled observation and to jump to large conclusions.

His chief sources of information are fishermen, farmers, stockbreeders, and hunters; to a lesser extent travelers, menageries, augurs, and drug manufacturers; and he owes a very little to such previous writers as Herodotus, Ctesias, Xenophon, Empedocles, and Democritus. There are many faulty reports that he corrects from observation. His favorite method is the counterinstance. He refutes that the viper does not slough its skin simply by describing an observation of the sloughing. The legend that the hyena has the genitalia of both sexes (which in fact it can appear to have externally) is refuted by inspection and dissection, and here he indicates that many specimens were examined. Fishermen said that all mullets are generated spontaneously, but he has examples of mullets with eggs and with sperm (although he allows that one kind of mullet is spontaneous).

where such direct checks are not possible, he refers to analogous examples or to theory. He denies that the cuckoo is a metamorphosed hawk on the grounds that the hawk preys on the cuckoo, a thing never seen done by one bird to another of its own kind. Fishermen believed what Herodotus also said, that fishes are impregnated by swallowing the sperm; Aristotle denies this because there is no connection between stomach and uterus, and because fishes have been observed in coition—which, he remarks, is difficult to observe, and fishermen have missed it because they are not interested in acquiring knowledge. Here he has been misled by faulty observation that, unluckily, agreed with theory—a coincidence that accounts for many of the mistakes in his reports. He held that where there are separate male and female, there must be coition. He knew that the male fish sprinkles the eggs with sperm after spawning, but thought this an additional process of fertilization. Another famous example is the fishermen’s report of hectocotylization—the extraordinary method by which a spermcarrying tentacle is inserted into the female’s mantle cavity and then completely detached from the male (eventually proved true): Aristotle denies that the tentacle assists reproduction, because it is not connected with the body and the spermatic channel—he was wrong because his theory could not accommodate what is, after all, a surprising fact. But in another context he makes it clear that theory must always yield to reliable observation: after his long discussion of the reproduction of bees he makes a statement that fairly represents his own practice (De generatione animalium 760b27):

This, then, appears to be the method of reproduction of bees, according to theory together with the apparent facts. But the facts have not been satisfactorily ascertained, and if ever they are, then credence must be given to observation rather than to theory, and to theory only in so far as it agrees with what is observed.

Many of the reports, however, are from firsthand observation. He refers sometimes to “the dissections,” evidently a collection of drawings and diagrams of internal organs; unfortunately nothing survives of them. Some of his data clearly come from deliberate dissection, while others come as clearly from casual observations in the kitchen or at augury. One of the best is a full-scale vivisection of a chameleon; and the internal organs of crabs, lobsters, cephalopods, and several fishes and birds are described from direct observation. Many of the exterior observations also presuppose a prolonged study. He speaks of lengthy investigations into the pairing of insects. He satisfies himself that birds produce wind eggs entirely in the absence of the cock. There are graphic accounts of courtship behavior, nest-building, and brood care. He records tests for sense perception in scallops, razor fish, and sponges. He watches the cuttlefish anchor itself to a rock by its two long arms when it is stormy. The detailing of structures in some crustaceans and shellfishes vividly suggests that the author is looking at the animal as he dictates. The sea urchin’s mouth parts are still known as “Aristotle’s lantern” from his description, and his statement that its eggs are larger at the full moon has only recently been confirmed for the Red Sea urchin. He is able to assert that two kinds of Serranidae are “always female” (they are in fact hermaphrodite). All such data require deliberate and patient observation. How much Aristotle himself did is not known, but it is clear enough that he caused reports to be collected and screened with great care.

The first main heading in the Historia animalium is “Parts of the Body.” Aristotle methodically lists the external and internal structures, noting the significant differences between animal types. Through drawing an analogy between legs and fins, he holds that fishes are moved primarily by their fins; this error creates difficulties for his theory of locomotion, whereby the blooded animals are moved by two or four points and the bloodless by more than four. He classifies the forms of uterus by position: rearward and ventral in the viviparous quadrupeds, forward and dorsal in the birds and oviparous quadrupeds, rearward and dorsal in the oviparous fishes, and “in both ways” in the ovoviviparous fishes—that is, extending from a forward dorsal to a rearward ventral position, because they first produce eggs and then hatch them within the uterus. There are various mistakes, mostly concerning man (where dissection was impossible) or the rarer animals. He is prone to accept them when they fall in with theory, thus accepting that men have more sutures in the skull than women (possibly based on an unlucky observation of a female skull with sutures effaced in pregnancy), for it fits his theory that men need more heat regulation in the brain. He reports that if one blows down the windpipe, the air reaches the heart: again a faulty observation that agreed with theory (that the pneuma in the heart is replenished from the lungs). His account of the heart’s three intercommunicating chambers, disastrous for later anatomy, was due to wrong observation in a difficult field, but it fell conveniently into his theory of the blood system.

Nevertheless, Aristotle is aware how easily observations can mislead. For example, he remarks that those who believed the lungs to be devoid of blood were misled by observing dissected animals from which the blood had escaped. Much of what he says of the lion is mistaken, as is his statement that the crocodile moves the upper jaw: in these cases external appearances have not been tested by inspection of the dead body. Some could have been better tested—for example, his reports of the incidence of the gall bladder are unreliable, probably because he trusted the augurs. But the great majority of data in this section are accurate and shrewdly observed, especially the details of alimentary canal and reproductive organs, in which he took special theoretical interest.

Under “Lives and Activities” Aristotle compares differences in reproductive, feeding, migration, hibernation, and sloughing, and variations due to season, breeding, disease, age, and habitat. His theory of reproduction, applied to all groups of animals, is argued in De generatione animalium; the Historia animalium summarizes this and adds much more information about sexual behavior, breeding methods and seasons, gestation, incubation, and brood care. He distinguishes the viviparous quadrupeds theoretically by the degree of perfection in the young at birth, and he has many details of seal and dolphin as well as land animals. The next step down is to the ovoviviparous, such as the vipers, sharks, and dogfishes. In them he describes the egg;s development and its movement rearward to the position where the young are released within the uterus; in one dogfish (Mustelus laevis ) he notes the placentoid structure, like that of mammals, which was not rediscovered until comparatively modern times. He mistakenly generalizes that all cartilaginous fishes are ovoviviparous. He divides the ovipara into those that lay perfected eggs (birds and quadrupeds) and those whose eggs develop after laying, requiring what he took to be a second fertilizing by the male. He describes minutely the development of the eggs of birds, fishes, cephalopods, and others by opening eggs at intervals during the whole incubation period. He records many special cases: for example, the way that Syngnathus acus carries its eggs in a pouch, which then splits to release them (although he does not observe that it is the male which carries them). The lowest mode of reproduction in his scale of “perfectedness” is spontaneous generation, which he attributes to all testaceans, many insects, the eel, and a few fishes. He describes the spawn of whelks, but judges it to be a budding-off comparable with that of plants, not a mass of eggs; otherwise, testaceans originate from various mixtures of mud and rotting substances, the type of animal being determined by the mixture. He considers that insects (except for one butterfly) produce grubs, not eggs, although one speaks of spiders’ or bees’ eggs, and so on, he says that what at first looks like an egg is really a motionless larva, on the (mistaken)grounds that the subsequent animal is formed out of the whole of it. The grubs of spiders, bees, cicadas, and others develop into the parental type, but those of flies and beetles do not develop further, and originate spontaneously from a variety of materials, which he lists. Gnats and mosquitoes do not even produce grubs, but themselves arise from grubs that are spontaneously generated. He describes many types of larval development through pupa to imago, including the change of the bloodworm into the gnat. His conclusion about the honeybee (which he says is a puzzle) is tentatively that the queen produces queens and workers, the workers produce the drones, and the drones produce nothing. His view here is not exactly parthenogenesis: he holds that bees contain both male and female principles, and therefore generate without coition.

The final section on “Characters,” that is, animal psychology and intelligence, contains little imputation of motives: he records strictly the observed behavior. He compares animals in compatibility, rivalry, nesting and homemaking, and miscellaneous habits of defense and self-support. Among many, for example, he reports the nests made by the octopus and the wrasse, and the brood care by the male river catfish—recently rediscovered and named after him (Parasilurus aristotelis ). He notes that the partridge makes two nests, on one of which the male sits; and his report that some partridges cackle and others whistle led to the discovery in 1962 that two populations (rock partridge and chukar) live side by side in Thrace. Among the honeybee’s habits he seems to refer to the “dance language.” The section is unfinished, and the treatise in its present form ends abruptly with a distinction between birds that take dust baths and those that take water baths.

The more complete descriptions, which have been inserted throughout the treatise and seem to be the latest additions, include those of the ape, chameleon, and wryneck, and extracts from Herodotus and Ctesias on the crocodile, hippopotamus, and martichoras. But most of the fabulous or unauthenticated reports are in a separate work called Mirabilia, where they were perhaps held awaiting corroboration: some of them—for example, the bison—are in both treatises. For entirely new animals, Aristotle no doubt required reliable eyewitnesses. But when it comes to details reportedof known animals, which is the subject matter of most of his reports, his first point of reference is the adult living animal in its natural environment. His standard of judgment is function rather than morphology, as he makes clear in De partibus animalium. The “analogies” that he seeks, and from which he constantly argues, are not structural but functional; and, wherever possible, his identification of differentiae is based on function. Because this is his aim in the Historia, he picks out the significant details better, for instance, than does Xenophon (whose excellent accounts of the hare and of horses provide the best contemporary comparison with Aristotle’s reports). Its change of plan and lack of revision make the treatise seem incoherent and bewildering, but its comprehensiveness and acumen made it the outstanding descriptive zoology of ancient times, even though it was not intended to be primarily descriptive. It outlasted the work of such later encyclopedic compilers as Pliny, and combined with Aristotle’s other zoological works it became—through the Arabic version translated into Latin by Michael Scot—the major ingredient in Albertus Magnus’ De anirnalibus, which dominated the field until the sixteenth century.

BIBLIOGRAPHY

The standard text is Bekker’s Corpus Aristotelicum with Latin trans. (Berlin, 1831–1870). There is also the text with English trans., intro., and brief notes in the Loeb Classical Library; see especially A. L. Peck’s eds. of De partibus animalium (rev. 1955), De generatione animalium (rev. 1953), and Historia animalium, I (1965; remaining 2 vols. in press). Parva naturalia was ed. with full English commentary by W. D. Ross (Oxford, 1955). The Loeb and Ross eds. contain bibliographies of previous eds. and full accounts of the MSS.

There are also lesser works with zoological content included in the Bekker ed., but not all are by Aristotle—De incessu animalium, De motu animalium, De spiritu, Mirabilia, and Problemata. See also The Works of Aristotle Translated Into English, W. D. Ross, ed.; III, De spiritu (1931); V. De incessu animalium and De motu animalium (1912); VI, Mirabilia (1913); and VII, Problemata (1927).

D. M. Balme