Aristotle's biology is the theory ofbiology, grounded in systematic observation and collection of data, mainlyzoological, embodied inAristotle's books on thescience. Many of his observations were made during his stay on the island ofLesbos, including especially his descriptions of themarine biology of the Pyrrha lagoon, now theGulf of Kalloni. His theory is based onhis concept of form, which derives from but is markedly unlikePlato'stheory of Forms.

The theory describes five major biological processes, namelymetabolism,temperature regulation, information processing,embryogenesis, andinheritance. Each was defined in some detail, in some cases sufficient to enable modern biologists to create mathematical models of themechanisms described. Aristotle's method, too, resembled the style of science used by modern biologists when exploring a new area, with systematic data collection, discovery of patterns, and inference of possible causal explanations from these. He did not perform experiments in the modern sense, but made observations of living animals and carried out dissections. He names some 500 species of bird, mammal, and fish; and he distinguishes dozens of insects and other invertebrates. He describes the internal anatomy of over a hundred animals, and dissected around 35 of these.

Aristotle's writings on biology, the first in thehistory of science, are scattered across several books, forming about a quarter of hiswritings that have survived. The main biology texts were theHistory of Animals,Generation of Animals,Movement of Animals,Progression of Animals,Parts of Animals, andOn the Soul, as well as the lost drawings ofThe Anatomies which accompanied theHistory.

Apart from his pupil,Theophrastus, who wrote a matchingEnquiry into Plants, no research of comparable scope was carried out inancient Greece, thoughHellenistic medicine in Egypt continued Aristotle's inquiry into the mechanisms of the human body. Aristotle's biology was influential in themedieval Islamic world. Translation of Arabic versions and commentaries into Latin brought knowledge of Aristotle back into Western Europe, but the only biological work widely taught in medieval universities wasOn the Soul. The association of his work with medievalscholasticism, as well as errors in his theories, causedEarly Modern scientists such asGalileo andWilliam Harvey to reject Aristotle. Criticism of his errors and secondhand reports continued for centuries. He has found better acceptance amongzoologists, and some of his long-derided observations inmarine biology have been found in modern times to be true.

Aristotle (384–322 BC) studied atPlato's Academy inAthens, remaining there for about 20 years. LikePlato, he soughtuniversals in hisphilosophy, but unlike Plato he backed up his views with detailed and systematic observation, notably of thenatural history of the island ofLesbos, where he spent about two years, and themarine life in the seas around it, especially of the Pyrrha lagoon in the island's centre.^[1] This study made him the earliest scientist whose written work survives. No similarly detailed work onzoology was attempted until the sixteenth century; accordingly Aristotle remained highly influential for some two thousand years. He returned to Athens and founded his own school, theLycaeum, where he taught for the last dozen years of his life. His writings on zoology form about a quarter of his surviving work.^[2] Aristotle's pupilTheophrastus later wrote a similar book onbotany,Enquiry into Plants.^[3]

Aristotle's biology is constructed on the basis ofhis theory of form, which is derived from Plato'stheory of Forms, but significantly different from it. Plato's Forms were eternal and fixed, being "blueprints in the mind of God".^[4] Real things in the world could, in Plato's view, at best be approximations to these perfect Forms. Aristotle heard Plato's view and developed it into a set of three biological concepts. He uses the same Greek word,εἶδος (eidos), to mean first of all the set of visible features that uniquely characterised a kind of animal. Aristotle used the word γένος (génos) to mean a kind.^[a] For example, the kind of animal called abird has feathers, a beak, wings, a hard-shelled egg, and warm blood.^[4]

Aristotle further noted that there are many bird forms within the bird kind –cranes,eagles,crows,bustards,sparrows, and so on, just as there are many forms offishes within the fish kind. He sometimes called theseatoma eidē, indivisible forms.^[b]Human is one of these indivisible forms: Socrates and the rest of us are all different individually, but we all have human form.^[4] More recent studies have shown that Aristotle used the terms γένος (génos) andεἶδος (eidos) in a relative way. A taxon that is considered an eidos in one context can be considered agénos (which includes variouseide) in another.^[5]

Finally, Aristotle observed that the child does not take just any form, but is given it by the parents' seeds, which combine. These seeds thus contain form, or in modern terms information.^[c] Aristotle makes clear that he sometimes intends this third sense by giving the analogy of awoodcarving. It takes its form from wood (its material cause); the tools and carving technique used to make it (its efficient cause); and the design laid out for it (itseidos or embedded information). Aristotle further emphasises the informational nature of form by arguing that a body is compounded of elements like earth and fire, just as a word is compounded of letters in a specific order.^[d][4]

As analysed by theevolutionary biologistArmand Leroi, Aristotle's biology included five major interlockingprocesses:^[6]

1. ametabolic process, whereby animals take in matter, change its qualities, and distribute these to use to grow, live, and reproduce
2. a cycle oftemperature regulation, whereby animalsmaintain a steady state, but which progressivelyfails in old age
3. an information processing model whereby animals receivesensory information, alter it in theseat of sensation,^[e] and use itto drive movements of the limbs. He thus separated sensation from thought, unlike all previous philosophers exceptAlcmaeon.^[8]
4. the process ofinheritance.
5. the processes ofembryonic development and ofspontaneous generation

The five processes formedwhat Aristotle called the soul: it was not something extra, but the system consisting exactly of these mechanisms. The Aristotelian soul died with the animal and was thus purely biological. Different types of organism possessed different types of soul. Plants had a vegetative soul, responsible for reproduction and growth. Animals had both a vegetative and a sensitive soul, responsible for mobility and sensation. Humans, uniquely, had a vegetative, a sensitive, and a rational soul, capable of thought and reflection.^[6][9][10]

Aristotle's account of metabolism sought to explain how food was processed by the body to provide both heat and the materials for the body's construction and maintenance. The metabolic system for live-bearing tetrapods^[f] described in theParts of Animals can be modelled as anopen system, a branching tree of flows of material through the body.^[11]

The system worked as follows. The incoming material, food, enters the body and is concocted into blood; waste is excreted as urine, bile, and faeces, and theelement fire is released as heat. Blood is made into flesh, the rest forming other earthy tissues such as bones, teeth, cartilages and sinews. Leftover blood is made intofat, whether softsuet or hard lard. Some fat from all around the body is made intosemen.^[11][12]

All the tissues are in Aristotle's view completely uniform parts with no internal structure of any kind; a cartilage for example was the same all the way through, notsubdivided into atoms asDemocritus (c. 460–c. 370 BC) had argued.^[13] The uniform parts can be arranged on a scale of Aristotelian qualities, from the coldest and driest, such as hair, to the hottest and wettest, such as milk.^[11][12]

At each stage of metabolism, residual materials are excreted as faeces, urine, and bile.^[11][12]

Aristotle's account of temperature regulation sought to explain how an animal maintained a steady temperature and the continued oscillation of the thorax needed for breathing. The system of regulation of temperature and breathing described inYouth and Old Age, Life and Death 26 is sufficiently detailed to permit modelling as anegative feedbackcontrol system (one that maintains a desired property by opposing disturbances to it), with a few assumptions such as a desired temperature to compare the actual temperature against.^[14]

The system worked as follows. Heat is constantly lost from the body. Food products reach the heart and are processed into new blood, releasing fire during metabolism, which raises the blood temperature too high. That raises the heart temperature, causing lung volume to increase, in turn raising the airflow at the mouth. The cool air brought in through the mouth reduces the heart temperature, so the lung volume accordingly decreases, restoring the temperature to normal.^[g][14]

The mechanism only works if the air is cooler than the reference temperature. If the air is hotter than that, the system becomes a positive feedback cycle, the body's fire is put out, and death follows. The system as described damps out fluctuations in temperature. Aristotle however predicted that his system would cause lung oscillation (breathing), which is possible given extra assumptions such as of delays or non-linear responses.^[14][16]

Aristotle'sinformation processing model has been named the "centralized incoming and outgoing motions model". It sought to explain how changes in the world led to appropriate behaviour in the animal.^[17]

The system worked as follows. The animal'ssense organ is altered when it detects an object. This causes a perceptual change in the animal'sseat of sensation, which Aristotle believed was the heart (cardiocentrism) rather than thebrain. This in turn causes a change in the heart's heat, which causes a quantitative change sufficient to make the heart transmit a mechanical impulse to a limb, which moves, moving the animal's body. The alteration in the heat of the heart also causes a change in the consistency of the joints, which helps the limb to move.^[17]

There is thus a causal chain which transmits information from a sense organ to an organ capable of making decisions, and onwards to a motor organ. In this respect, the model is analogous to a modern understanding of information processing such as insensory-motor coupling.^[18][17]

Aristotle's inheritance model sought to explain how the parents' characteristics are transmitted to the child, subject to influence from the environment.^[19][h]

The system worked as follows. The father's semen and the mother's menses have movements that encode their parental characteristics.^[19][20] The model is partly asymmetric, as only the father's movements definethe form oreidos of the species, while the movements of both the father's and the mother's uniform parts define features other than the form, such as the father's eye colour or the mother's nose shape.^[19]

Aristotle's theory has some symmetry, as semen movements carry maleness while the menses carry femaleness. If the semen is hot enough to overpower the cold menses, the child will be a boy; but if it is too cold to do this, the child will be a girl. Inheritance is thusparticulate (definitely one trait or another), as inMendelian genetics, unlike theHippocratic model which was continuous andblending.^[19]

The child's sex can be influenced by factors that affect temperature, including the weather, the wind direction, diet, and the father's age. Features other than sex also depend on whether the semen overpowers the menses, so if a man has strong semen, he will have sons who resemble him, while if the semen is weak, he will have daughters who resemble their mother.^[i][19]

Aristotle's model ofembryogenesis sought to explain how the inherited parental characteristics cause the formation and development of an embryo.^[21]

The system worked as follows. First, the father's semen curdles the mother's menses, which Aristotle compares with howrennet (anenzyme from a cow's stomach) curdles milk incheesemaking. This forms the embryo; it is then developed by the action of thepneuma (literally, breath or spirit) in the semen. Thepneuma first makes the heart appear; this is vital, as the heart nourishes all other organs. Aristotle observed that the heart is the first organ seen to be active (beating) in a hen's egg. Thepneuma then makes the other organs develop.^[21]

Aristotle asserts in hisPhysics that according toEmpedocles, order "spontaneously" appears in the developing embryo. InThe Parts of Animals, he argues that what he describes as a theory of Empedocles, that thevertebral column is divided into vertebrae because, as it happens, the embryo twists about and snaps the column into pieces, is wrong. Aristotle argues instead that the process has a predefined goal: that the "seed" that develops into the embryo began with an inbuilt "potential" to become specific body parts, such as vertebrae. Further, each sort of animal gives rise to animals of its own kind: humans only have human babies.^[22]

Aristotle has been called unscientific^[23] by philosophers fromFrancis Bacon onwards^[23] for at least two reasons: his scientific style,^[24] and his use ofexplanation. His explanations are in turn made cryptic by his complicatedsystem of causes.^[23] However, these charges need to be considered in the light of what was known in his own time.^[23] His systematic gathering of data, too, is obscured by the lack of modern methods of presentation, such as tables of data: for example, the whole ofHistory of Animals Book VI is taken up with a list of observations of the life histories of birds that "would now be summarized in a single table inNature – and in the Online Supplementary Information at that".^[25]

Aristotle did not doexperiments in the modern sense.^[26] He used the ancient Greek termpepeiramenoi to mean observations, or at most investigative procedures,^[27] such as (inGeneration of Animals) finding a fertilised hen's egg of a suitable stage and opening it so as to be able to see the embryo's heart inside.^[28]

Instead, he practised a different style of science: systematically gathering data, discovering patterns common to whole groups of animals, and inferring possible causal explanations from these.^[24][29] This style is common in modern biology when large amounts of data become available in a new field, such asgenomics. It does not result in the same certainty as experimental science, but it sets outtestable hypotheses and constructs a narrative explanation of what is observed. In this sense, Aristotle's biology is scientific.^[24]

From the data he collected and documented, Aristotle inferred quite a number ofrules relating the life-history features of the live-bearing tetrapods (terrestrial placental mammals^[j]) that he studied. Among these correct predictions are the following. Brood size decreases with (adult) body mass, so that anelephant has fewer young (usually just one) per brood than amouse.Lifespan increases withgestation period, and also with body mass, so that elephants live longer than mice, have a longer period of gestation, and are heavier. As a final example,fecundity decreases with lifespan, so long-lived kinds like elephants have fewer young in total than short-lived kinds like mice.^[30]

Aristotle's use of explanation has been considered "fundamentally unscientific".^[23] The French playwrightMolière's 1673 playThe Imaginary Invalid portrays thequack Aristotelian doctor Argan blandly explaining that opium causes sleep by virtue of itsdormitive [sleep-making] principle, itsvirtus dormitiva.^[k][31] Argan's explanation is at best empty (devoid of mechanism),^[23] at worstvitalist. But the real Aristotle did providebiological mechanisms, in the form of the five processes of metabolism, temperature regulation, information processing, embryonic development, and inheritance that he developed. Further, he provided mechanical, non-vitalist analogies for these theories, mentioningbellows, toy carts, the movement of water through porous pots, and even automatic puppets.^[23]

Readers of Aristotle have found thefour causes that he uses in his biological explanations opaque,^[32] something not helped by many centuries of confusedexegesis. For a biological system, these are however straightforward enough. The material cause is simply what a system is constructed from. The goal (final cause) and formal cause arewhat something is for, itsfunction: to a modernbiologist, such teleology describesadaptation under the pressure ofnatural selection. The efficient cause is how a system develops and moves: to a modern biologist, those are explained bydevelopmental biology andphysiology. Biologists continue to offerexplanations of these same kinds.^[32][23]

Aristotle was the first person to study biology systematically. He spent two years observing and describing the zoology ofLesbos and the surrounding seas, including in particular thePyrrha lagoon in the centre of Lesbos.^[1][33] His data are assembled from his own observations, statements given by people with specialised knowledge such asbeekeepers andfishermen, and less accurate accounts provided by travellers from overseas.^[34]

His observations oncatfish,electric fish (Torpedo) andangler fish are detailed, as is his writing oncephalopods including theoctopus,cuttlefish andpaper nautilus.^[35] He reported that fishermen had asserted that the octopus'shectocotyl arm was used in sexual reproduction.^[36][37] He admitted its use in mating 'only for the sake of attachment', but rejected the idea that it was useful for generation, since "it is outside the passage and indeed outside the body".^[38] In the 19th century, biologists found that the reported function was correct. He separated the aquatic mammals from fish, and knew thatsharks andrays were part of the group he calledSelachē (roughly, the modern zoologist'sselachians^[l]).^[35]

Aristotle recorded that theembryo ofa dogfish (left) was attached by a cord to something like a mammalianplacenta (right), in fact ayolk sac.^[40]

Among many other things, he gave accurate descriptions of the four-chambered stomachs ofruminants, and of theovoviviparous embryological development of thedogfish.^[40][41] His accounts of about 35 animals are sufficiently detailed to convince biologists that hedissected those species,^[42] indeedvivisecting some;^[43] he mentions the internal anatomy of roughly 110 animals in total.^[42]

Aristotle distinguished about 500 species of birds, mammals,actinopterygians andselachians inHistory of Animals andParts of Animals.^[44][45][46] Aristotle distinguished animals with blood,Enhaima (the modern zoologist'svertebrates) and animals without blood,Anhaima (invertebrates).^[m][47][48]

Animals with blood included live-bearing tetrapods,Zōiotoka tetrapoda (roughly, themammals), being warm, having four legs, and giving birth to their young.Thecetaceans,Kētōdē, also had blood and gave birth to live young, but did not have legs, and therefore formed a separate group^[n] (megista genē, defined by a set of functioning "parts"^[49]).^[50]The birds,Ornithes had blood and laid eggs, but had only 2 legs and were a distinct form (eidos) with feathers and beaks instead of teeth, so they too formed a distinct group, of over 50 kinds. The egg-bearing tetrapods,Ōiotoka tetrapoda (reptiles andamphibians) had blood and four legs, but were cold and laid eggs, so were a distinct group. Thesnakes,Opheis, similarly had blood, but no legs, and laid dry eggs, so were a separate group.Thefishes,Ikhthyes, had blood but no legs, and laid wet eggs, forming a definite group. Among them, the selachiansSelakhē (sharks and rays), hadcartilages instead of bones^[47] and were viviparous (Aristotle did not know that some selachians are oviparous).^[51]

Animals without blood were divided into soft-shelledMalakostraka (crabs,lobsters, andshrimps); hard-shelledOstrakoderma (gastropods andbivalves); soft-bodiedMalakia (cephalopods); and divisible animalsEntoma (insects,spiders,scorpions,ticks). Other animals without blood includedfish lice,hermit crabs,red coral,sea anemones,sponges,starfish and various worms: Aristotle did not classify these into groups, although Aristotle mentioned that thesea anemone was in its "own group".^[51]

Aristotle stated in theHistory of Animals that all beings were arranged in a fixed scale of perfection, reflected in their form (eidos).^[o] They stretched from minerals to plants and animals, and on up to man, forming thescala naturae or great chain of being.^[52][53] His system had eleven grades, arranged according to the potentiality of each being, expressed in their form at birth. The highest animals gave birth to warm and wet creatures alive, the lowest bore theirs cold, dry, and in thick eggs.^[35] The system was based on Aristotle's interpretation of thefour elements in hisOn Generation and Corruption:Fire (hot and dry);Air (hot and wet);Water (cold and wet); andEarth (cold and dry). These are arranged from the most energetic to the least, so the warm, wet young raised in awomb with aplacenta were higher on the scale than the cold, dry, nearly mineral eggs of birds.^[54][10] However, Aristotle is careful never to insist that a group fits perfectly in the scale; he knows animals have many combinations of attributes, and that placements are approximate.^[55]

Aristotle's pupil and successor at theLyceum,Theophrastus, wrote theHistory of Plants, the first classical book ofbotany. It has an Aristotelian structure, but rather than focus on formal causes, as Aristotle did, Theophrastus described how plants functioned.^[56][57] Where Aristotle expanded on grand theories, Theophrastus was quietly empirical.^[58] Where Aristotle insisted that species have a fixed place on thescala naturae, Theophrastus suggests that one kind of plantcan transform into another, as when a field sown towheat turns to the weeddarnel.^[59]

After Theophrastus, though interest in Aristotle's ideas survived, they were generally taken unquestioningly.^[60] It is not until the age ofAlexandria under thePtolemies that advances in biology resumed. The first medical teacher at Alexandria,Herophilus of Chalcedon, corrected Aristotle, placing intelligence in thebrain, and connected thenervous system to motion and sensation. Herophilus also distinguished betweenveins andarteries, noting that the latterpulse while the former do not.^[61]

Manyclassical works including those of Aristotle were transmitted from Greek to Syriac, then to Arabic, then to Latin in the Middle Ages. Aristotle remained the principal authority in biology for the next two thousand years.^[62] TheKitāb al-Hayawān (كتاب الحيوان,Book of Animals) is a 9th-centuryArabic translation ofHistory of Animals: 1–10,On the Parts of Animals: 11–14,^[63] andGeneration of Animals: 15–19.^[64][65]

The book was mentioned byAl-Kindī (d. 850), and commented on byAvicenna (Ibn Sīnā) in hisKitāb al-Šifā (کتاب الشفاء,The Book of Healing).Avempace (Ibn Bājja) andAverroes (Ibn Rushd) commented onOn the Parts of Animals andGeneration of Animals, Averroes criticising Avempace's interpretations.^[66]

When the Christian kingAlfonso VI of Castileconquered Toledo from the Moors in 1085, an Arabic translation of Aristotle's works, with commentaries byAvicenna andAverroes emerged into Europeanmedieval scholarship.Michael Scot translated much of Aristotle's biology into Latin, c. 1225, along with many of Averroes's commentaries.^[p]Albertus Magnus commented extensively on Aristotle, but added his own zoological observations and an encyclopedia of animals based onThomas of Cantimpré. Later in the 13th century,Thomas Aquinas merged Aristotle's metaphysics with Christian theology. Whereas Albert had treated Aristotle's biology as science, writing that experiment was the only safe guide and joining in with the types of observation that Aristotle had made, Aquinas saw Aristotle purely as theory, and Aristotelian thought became associated withscholasticism.^[66] The scholasticnatural philosophy curriculum omitted most of Aristotle's biology, but includedOn the Soul.^[68]

Renaissance zoologists made use of Aristotle's zoology in two ways. Especially in Italy, scholars such asPietro Pomponazzi andAgostino Nifo lectured and wrote commentaries on Aristotle. Elsewhere, authors used Aristotle as one of their sources, alongside their own and their colleagues' observations, to create new encyclopedias such asKonrad Gessner's 1551Historia Animalium.^[q] The title and the philosophical approach were Aristotelian, but the work was largely new.Edward Wotton similarly helped to found modern zoology by arranging the animals according to Aristotle's theories, separating out folklore from his 1552De differentiis animalium.^[68][69] Aristotle's system of classification had thus remained influential for many centuries.^{[70][51][71][72]}

In theEarly Modern period, Aristotle came to represent all that was obsolete, scholastic, and wrong, not helped by his association with medieval theology. In 1632,Galileo representedAristotelianism in hisDialogo sopra i due massimi sistemi del mondo (Dialogue Concerning the Two Chief World Systems) by thestrawman Simplicio ("Simpleton"^[73]). That same year,William Harvey proved Aristotle wrong by demonstrating thatblood circulates.^[74][75]

Aristotle still represented the enemy of true science into the 20th century. Leroi noted that in 1985,Peter Medawar stated in "pure seventeenth century"^[76] tones that Aristotle had assembled "a strange and generally speaking rather tiresomefarrago ofhearsay, imperfect observation, wishful thinking and credulity amounting to downright gullibility".^[76][77]

Zoologists working in the 19th century, includingGeorges Cuvier,Johannes Peter Müller,^[78] andLouis Agassiz admired Aristotle's biology and investigated some of his observations.D'Arcy Thompson translatedHistory of Animals in 1910, making aclassically educated zoologist's informed attempt to identify the animals that Aristotle names, and to interpret and diagram his anatomical descriptions.^{[79][80][81][82]}

Charles Darwinquoted a passage fromAristotle'sPhysics II 8 inThe Origin of Species, which entertains the possibility of a selection process following the random combination of body parts. Darwin comments that "We here see the principle of natural selection shadowed forth".^[83] However, two things mitigate against this interpretation. Firstly, Aristotle immediately rejected the possibility of such a process of assembling body parts. Secondly, according to Leroi, Aristotle was in any case discussingontogeny, theEmpedoclean coming into being of an individual from component parts, notphylogeny andnatural selection.^[84] Darwin considered Aristotle the most important early contributor to biological thought; in an 1882 letter he wrote that "Linnaeus and Cuvier have been my two gods, though in very different ways, but they were mere schoolboys to old Aristotle."^[85][86]

Zoologists have frequently mocked Aristotle for errors and unverified secondhand reports. However, modern observation has confirmed one after another of his more surprising claims,^[68] including theactive camouflage of the octopus^[87] and the ability of elephants tosnorkel with their trunks while swimming.^[88]

Aristotle remains largely unknown to modern scientists, though zoologists are perhaps most likely to mention him as "the father of biology";^[89] the MarineBio Conservation Society notes that he identified "crustaceans,echinoderms,mollusks, andfish", thatcetaceans aremammals, and that marine vertebrates could be eitheroviparous orviviparous, so he "is often referred to as the father ofmarine biology".^[r][90] Few practicing zoologists explicitly adhere to Aristotle's great chain of being, but its influence is still perceptible in the use of the terms "lower" and "upper" to designate taxa such as groups of plants.^[91]The evolutionary zoologistArmand Leroi has taken an interest in Aristotle's biology.^[s][93] The concept ofhomology began with Aristotle,^[94] and theevolutionary developmental biologistLewis I. Held commented that^[95]

The deep thinker who would be most amused by ..deep homologies is Aristotle, who was fascinated by the natural world but bewildered by its inner workings.^[95]

Aristotle did not write anything that resembles a modern, unified textbook of biology. Instead, he wrote a large number of "books" which, taken together, give an idea of his approach to the science. Some of these interlock, referring to each other, while others, such as the drawings ofThe Anatomies are lost, but referred to in theHistory of Animals, where the reader is instructed to look at the diagrams to understand how the animal parts described are arranged,^[96] and it has even been possible to reconstruct (admittedly with much associated uncertainty) what some of these illustrations may have looked like, from Aristotle's descriptions.^[97]

Aristotle's main biological works are the five books sometimes grouped asOn Animals (De Animalibus), namely, with the conventional abbreviations shown in parentheses:

• History of Animals, orInquiries into Animals (Historia Animalium) (HA)
• Generation of Animals (De Generatione Animalium) (GA)
• Movement of Animals (De Motu Animalium) (DM)
• Parts of Animals (De Partibus Animalium) (PA)
• Progression of Animals orOn the Gait of Animals (De Incessu Animalium) (IA)

together withOn the Soul (De Anima) (DA).^[68]

In addition, a group of seven short works, conventionally forming theParva Naturalia ("Short treatises on Nature"), is also mainly biological:

• Sense and Sensibilia^[98] (Sense)
• On Memory^[99]
• On Sleep^[100]
• On Dreams^[101]
• On Divination in Sleep^[102]
• On Length and Shortness of Life^[103]
• On Youth, Old Age, Life and Death, and Respiration^[104]

• Guthrie, W. K. C. (1981).A History of Greek Philosophy. Vol. 1.Cambridge University Press.
• Leroi, Armand Marie (2010). "Function and Constraint in Aristotle and Evolutionary Theory". In Föllinger, S. (ed.).Was ist 'Leben'? Aristoteles' Anschauungen zur Entstehung und Funktionsweise von Leben. Franz Steiner Verlag. pp. 261–284.
• Leroi, Armand Marie (2014).The Lagoon: How Aristotle Invented Science. Bloomsbury.ISBN 978-1-4088-3622-4.
• Mason, Stephen F. (1962) [1953].A History of the Sciences. P. F. Collier.ISBN 0-02-093400-9.{{cite book}}:ISBN / Date incompatibility (help)
• Mayr, Ernst (1985).The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Harvard University Press.ISBN 978-0-674-36446-2.
• Ogilvie, Brian W. (2010). "Zoology". In Grafton, Anthony; Most, Glenn W.; Settis, Salvatore (eds.).The Classical Tradition. Harvard University Press. pp. 1000–1001.ISBN 978-0-674-07227-5.
• Singer, Charles (1931).A Short History of Biology. Oxford University Press.
• Taylor, Henry Osborn (1922). "Chapter 3: Aristotle's Biology".Greek Biology and Medicine. Archived from the original on 27 March 2006.
• Thompson, D'Arcy Wentworth (1910). "Historia animalium". In Ross, W. D.; Smith, J. A. (eds.).The works of Aristotle translated into English. Clarendon Press.
• Thompson, D'Arcy Wentworth (1913).On Aristotle as a biologist. Clarendon Press.

• History of biology
• Philosophy of Aristotle
• History of zoology
• Ancient Greek science

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