Aristotle's biology
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Aristotle's biology is the theory of
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process heredita ...
, grounded in systematic observation and collection of data, mainly zoological, embodied in
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
's books on the
science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidenc ...
. Many of his observations were made during his stay on the island of Lesbos, including especially his descriptions of the marine biology of the Pyrrha lagoon, now the Gulf of Kalloni. His theory is based on his concept of form, which derives from but is markedly unlike
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first instit ...
's theory of Forms. The theory describes five major biological processes, namely
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
, temperature regulation, information processing, embryogenesis, and inheritance. Each was defined in some detail, in some cases sufficient to enable modern biologists to create mathematical models of the mechanisms 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 the history of science, are scattered across several books, forming about a quarter of his writings that have survived. The main biology texts were the ''
History of Animals ''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'', '' Generation of Animals'', '' Movement of Animals'', '' Progression of Animals'', '' Parts of Animals'', and '' On the Soul'', as well as the lost drawings of ''The Anatomies'' which accompanied the ''History''. Apart from his pupil, Theophrastus, who wrote a matching '' Enquiry into Plants'', no research of comparable scope was carried out in
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages The term Greek Dark Ages refers to the period of Greek history from the end of the Mycenaean palatial civiliz ...
, though
Hellenistic In Classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the in ...
medicine in Egypt continued Aristotle's inquiry into the mechanisms of the human body. Aristotle's biology was influential in the
medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
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 was ''On the Soul''. The association of his work with medieval scholasticism, as well as errors in his theories, caused Early Modern scientists such as
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer An astronomer is a scientist A scientist is a person who conducts scientific research to advance knowledge in an area of ...
and
William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician A physician (American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language ...
to reject Aristotle. Criticism of his errors and secondhand reports continued for centuries. He has found better acceptance among zoologists, and some of his long-derided observations in marine biology have been found in modern times to be true.


Context


Aristotle's background

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
(384–322 BC) studied at Plato's Academy in
Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital city, capital and List of cities and towns in Greece, largest city of Greece. With a population close to four million, it is also the seventh List ...
, remaining there for about 20 years. Like
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first instit ...
, he sought universals in his
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. ...
, but unlike Plato he backed up his views with detailed and systematic observation, notably of the natural history of the island of Lesbos, where he spent about two years, and the marine life in the seas around it, especially of the Pyrrha lagoon in the island's centre. This study made him the earliest scientist whose written work survives. No similarly detailed work on
zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several un ...
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, the Lycaeum, where he taught for the last dozen years of his life. His writings on zoology form about a quarter of his surviving work. Aristotle's pupil Theophrastus later wrote a similar book on botany, ''Enquiry into Plants''.


Aristotelian forms

Aristotle's biology is constructed on the basis of his theory of form, which is derived from Plato's theory of Forms, but significantly different from it. Plato's Forms were eternal and fixed, being "blueprints in the mind of God". 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, (''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. For example, the kind of animal called a
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, ...
has feathers, a beak, wings, a hard-shelled egg, and warm blood. 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 of
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...
es within the fish kind. He sometimes called these ''atoma eidē'', indivisible forms.
Human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cult ...
is one of these indivisible forms: Socrates and the rest of us are all different individually, but we all have human form. 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. Aristotle makes clear that he sometimes intends this third sense by giving the analogy of a woodcarving. 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 (its ''eidos'' 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.


System


Soul as system

As analysed by the evolutionary biologist Armand Leroi, Aristotle's biology included five major interlocking processes: # a metabolic process, whereby animals take in matter, change its qualities, and distribute these to use to grow, live, and reproduce # a cycle of temperature regulation, whereby animals maintain a steady state, but which progressively fails in old age # an information processing model whereby animals receive sensory information, alter it in the seat of sensation, and use it to drive movements of the limbs. He thus separated sensation from thought, unlike all previous philosophers except Alcmaeon. # the process of inheritance. # the processes of
embryonic development An embryo is an initial stage of development of a multicellular organism. In organism In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that ti ...
and of spontaneous generation The five processes formed what 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.


Processes


Metabolism

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 described in the ''Parts of Animals'' can be modelled as an open system, a branching tree of flows of material through the body. 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 the element 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 into fat, whether soft suet or hard lard. Some fat from all around the body is made into
semen Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum ...
. 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, not subdivided into atoms as Democritus (c. 460–c. 370 BC) had argued. 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. At each stage of metabolism, residual materials are excreted as faeces, urine, and bile.


Temperature regulation

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 in ''Youth and Old Age, Life and Death'' 26 is sufficiently detailed to permit modelling as a
negative feedback Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by othe ...
control system A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial ...
(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. 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. 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.


Information processing

Aristotle's information 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. The system worked as follows. The animal's sense organ is altered when it detects an object. This causes a perceptual change in the animal's seat of sensation, which Aristotle believed was the heart ( cardiocentrism) rather than the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ i ...
. 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. 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 in sensory-motor coupling.


Inheritance

Aristotle's inheritance model sought to explain how the parents' characteristics are transmitted to the child, subject to influence from the environment. The system worked as follows. The father's semen and the mother's menses have movements that encode their parental characteristics. The model is partly asymmetric, as only the father's movements define the form or ''eidos'' 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. 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 thus particulate (definitely one trait or another), as in Mendelian genetics, unlike the Hippocratic model which was continuous and blending. 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.


Embryogenesis

Aristotle's model of embryogenesis sought to explain how the inherited parental characteristics cause the formation and development of an embryo. The system worked as follows. First, the father's semen curdles the mother's menses, which Aristotle compares with how rennet (an
enzyme Enzymes () are protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic rea ...
from a cow's stomach) curdles milk in cheesemaking. This forms the embryo; it is then developed by the action of the ''pneuma'' (literally, breath or spirit) in the semen. The ''pneuma'' 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. The ''pneuma'' then makes the other organs develop.


Method

Aristotle has been called unscientific by philosophers from Francis Bacon onwards for at least two reasons: his scientific style, and his use of explanation. His explanations are in turn made cryptic by his complicated system of causes. However, these charges need to be considered in the light of what was known in his own time. 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 of ''
History of Animals ''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'' 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 in ''
Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science Science is ...
'' – and in the Online Supplementary Information at that".


Scientific style

Aristotle did not do experiments in the modern sense. He used the ancient Greek term ''pepeiramenoi'' to mean observations, or at most investigative procedures, such as (in ''Generation 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. 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. This style is common in modern biology when large amounts of data become available in a new field, such as
genomics Genomics is an interdisciplinary field of biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, three-dime ...
. It does not result in the same certainty as experimental science, but it sets out testable hypotheses and constructs a narrative explanation of what is observed. In this sense, Aristotle's biology is scientific. From the data he collected and documented, Aristotle inferred quite a number of rules relating the life-history features of the live-bearing tetrapods (terrestrial placental mammals) that he studied. Among these correct predictions are the following. Brood size decreases with (adult) body mass, so that an
elephant Elephants are the largest existing land animals. Three living species In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a s ...
has fewer young (usually just one) per brood than a
mouse A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus ...
. Lifespan increases with gestation 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 Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility Fertility is the capa ...
decreases with lifespan, so long-lived kinds like elephants have fewer young in total than short-lived kinds like mice.


Mechanism and analogy

Aristotle's use of explanation has been considered "fundamentally unscientific". The French playwright Molière's 1673 play '' The Imaginary Invalid'' portrays the quack Aristotelian doctor Argan blandly explaining that opium causes sleep by virtue of its dormitive leep-makingprinciple, its ''virtus dormitiva''. Argan's explanation is at best empty (devoid of mechanism), at worst vitalist. But the real Aristotle did provide biological 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, mentioning
bellows A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtig ...
, toy carts, the movement of water through porous pots, and even automatic puppets.


Complex causality

Readers of Aristotle have found the
four causes The four causes or four explanations are, in Aristotelian thought, four fundamental types of answer to the question "why?", in analysis of change or movement in nature: the material, the formal, the efficient, and the final. Aristotle ...
that he uses in his biological explanations opaque, something not helped by many centuries of confused
exegesis Exegesis ( ; from the Greek , from , "to lead out") is a critical explanation or interpretation of a text. The term is traditionally applied to the interpretation of Biblical works. In modern usage, exegesis can involve critical interpretatio ...
. 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 are what something is for, its function: to a modern biologist, such teleology describes adaptation under the pressure of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism In biology ...
. The efficient cause is how a system develops and moves: to a modern biologist, those are explained by
developmental biology Developmental biology is the study of the process by which animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able t ...
and
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying ...
. Biologists continue to offer explanations of these same kinds.


Empirical research

Aristotle was the first person to study biology systematically. He spent two years observing and describing the zoology of Lesbos and the surrounding seas, including in particular the Pyrrha lagoon in the centre of Lesbos. His data are assembled from his own observations, statements given by people with specialised knowledge such as beekeepers and fishermen, and less accurate accounts provided by travellers from overseas. His observations on
catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species al ...
, electric fish (''
Torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead A warhead is the forward section of a device that contains the explosive agent or tox ...
'') and angler fish are detailed, as is his writing on
cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapod ...
s including the
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species In biology Biology is the scientific study of life ...
,
cuttlefish Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid True squid are ...
and paper nautilus. He reported that fishermen had asserted that the octopus’s hectocotyl arm was used in sexual reproduction. 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". In the 19th century, biologists found that the reported function was correct. He separated the aquatic mammals from fish, and knew that
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade A ...
s and rays were part of the group he called ''Selachē'' (roughly, the modern zoologist's selachians). Among many other things, he gave accurate descriptions of the four-chambered stomachs of
ruminant Ruminants (suborder Ruminantia) are ungulate, hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principally ...
s, and of the ovoviviparous embryological development of the dogfish. His accounts of about 35 animals are sufficiently detailed to convince biologists that he dissected those species, indeed vivisecting some; he mentions the internal anatomy of roughly 110 animals in total.


Classification

Aristotle distinguished about 500 species of birds, mammals and fishes in ''History of Animals'' and '' Parts of Animals''. His system of classification, one of the earliest in scientific taxonomy, was influential for over two thousand years. Aristotle distinguished animals with blood, ''Enhaima'' (the modern zoologist's vertebrates) and animals without blood, ''Anhaima'' (
invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordata, ...
). Animals with blood included live-bearing tetrapods, ''Zōiotoka tetrapoda'' (roughly, the mammals), being warm, having four legs, and giving birth to their young. The
cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whale Whales are a widely distributed and diverse group of fully Aquatic ecosystem, aquatic placental mammal, placental marine mammals. As an informal and Colloquialis ...
ns, ''Kētōdē'', also had blood and gave birth to live young, but did not have legs, and therefore formed a separate group (''megista genē'', defined by a set of functioning "parts"). 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'' (
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtle Turtles are an order of reptiles known as Testudines, ch ...
s and amphibians) had blood and four legs, but were cold and laid eggs, so were a distinct group. The
snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several mor ...
s, ''Opheis'', similarly had blood, but no legs, and laid dry eggs, so were a separate group. The fishes, ''Ikhthyes'', had blood but no legs, and laid wet eggs, forming a definite group. Among them, the selachians ''Selakhē'' (sharks and rays), had
cartilage Cartilage is a resilient and smooth type of connective tissue Connective tissue is one of the four primary types of animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, anim ...
s instead of bones. Animals without blood were divided into soft-shelled ''Malakostraka'' ( crabs, lobsters, and shrimps); hard-shelled ''Ostrakoderma'' (
gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrate Invertebrates are a paraphyletic group of animal Animals are multicellular, eukaryotic organisms in the biological kingdom ...
and
bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...
); soft-bodied ''Malakia'' (
cephalopods A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapod ...
); and divisible animals ''Entoma'' (
insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
, spiders,
scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always e ...
s, ticks). Other animals without blood included fish lice, hermit crabs, red coral, sea anemones, sponges, starfish and various worms: Aristotle did not classify these into groups.


Scale of being

Aristotle stated in the ''History of Animals'' that all beings were arranged in a fixed scale of perfection, reflected in their form (''eidos''). They stretched from minerals to plants and animals, and on up to man, forming the '' ''scala naturae'' or great chain of being''. 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. The system was based on Aristotle's interpretation of the four elements in his '' On Generation and Corruption'':
Fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. At a certain point in the combustion reaction, called the ignition ...
(hot and dry); Air (hot and wet);
Water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts a ...
(cold and wet); and
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
(cold and dry). These are arranged from the most energetic to the least, so the warm, wet young raised in a womb with a
placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mat ...
were higher on the scale than the cold, dry, nearly mineral eggs of birds. 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.


Influence


On Theophrastus

Aristotle's pupil and successor at the Lyceum, Theophrastus, wrote the '' History of Plants'', the first classical book of botany. It has an Aristotelian structure, but rather than focus on formal causes, as Aristotle did, Theophrastus described how plants functioned. Where Aristotle expanded on grand theories, Theophrastus was quietly empirical. Where Aristotle insisted that species have a fixed place on the ''scala naturae'', Theophrastus suggests that one kind of plant can transform into another, as when a field sown to
wheat Wheat is a grass widely cultivated for its seed, a cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit In botany, a fruit is the seed-bearing structure in flowering p ...
turns to the weed darnel.


On Hellenistic medicine

After Theophrastus, though interest in Aristotle's ideas survived, they were generally taken unquestioningly.Annas, "Classical Greek Philosophy", 2001, p. 252. In Boardman, John; Griffin, Jasper; Murray, Oswyn (ed.) ''The Oxford History of the Classical World''.
Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford The University of Oxford is a collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest unive ...
.
It is not until the age of
Alexandria Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinent ...
under the Ptolemies that advances in biology resumed. The first medical teacher at Alexandria, Herophilus of Chalcedon, corrected Aristotle, placing intelligence in the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ i ...
, and connected the
nervous system In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells tha ...
to motion and sensation. Herophilus also distinguished between veins and arteries, noting that the latter pulse while the former do not.


On Islamic zoology

Many classical 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. The '' Kitāb al-Hayawān'' (كتاب الحيوان, ''Book of Animals'') is a 9th-century
Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walte ...
translation of ''History of Animals'': 1–10, ''On the Parts of Animals'': 11–14, and ''Generation of Animals'': 15–19. The book was mentioned by Al-Kindī (d. 850), and commented on by Avicenna (Ibn Sīnā) in his '' Kitāb al-Šifā'' (کتاب الشفاء, ''The Book of Healing''). Avempace (Ibn Bājja) and Averroes (Ibn Rushd) commented on ''On the Parts of Animals'' and ''Generation of Animals'', Averroes criticising Avempace's interpretations.


On medieval science

When the Christian Alfonso VI of Castile retook the Kingdom of Toledo from the Moors in 1085, an Arabic translation of Aristotle's works, with commentaries by Avicenna and Averroes emerged into European
medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
scholarship. Michael Scot translated much of Aristotle's biology into Latin, c. 1225, along with many of Averroes's commentaries. Albertus Magnus commented extensively on Aristotle, but added his own zoological observations and an encyclopedia of animals based on Thomas of Cantimpré. Later in the 13th century,
Thomas Aquinas Thomas Aquinas, OP (; it, Tommaso d'Aquino, lit=Thomas of Aquino; 1225 – 7 March 1274) was an Italian Dominican friar A friar is a member of one of the mendicant orders founded in the twelfth or thirteenth century; the term disti ...
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 with scholasticism. The scholastic natural philosophy curriculum omitted most of Aristotle's biology, but included ''On the Soul''.


On Renaissance science

Renaissance zoologists made use of Aristotle's zoology in two ways. Especially in Italy, scholars such as Pietro Pomponazzi and Agostino 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 as Konrad Gessner's 1551 '' Historia Animalium''. 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 1552 ''De differentiis animalium''.


Early Modern rejection

In the Early Modern period, Aristotle came to represent all that was obsolete, scholastic, and wrong, not helped by his association with medieval theology. In 1632,
Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer An astronomer is a scientist A scientist is a person who conducts scientific research to advance knowledge in an area of ...
represented Aristotelianism in his '' Dialogo sopra i due massimi sistemi del mondo'' (Dialogue Concerning the Two Chief World Systems) by the strawman Simplicio ("Simpleton"). That same year,
William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician A physician (American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language ...
proved Aristotle wrong by demonstrating that blood circulates. Aristotle still represented the enemy of true science into the 20th century. Leroi noted that in 1985, Peter Medawar stated in "pure seventeenth century" tones that Aristotle had assembled "a strange and generally speaking rather tiresome farrago of hearsay, imperfect observation, wishful thinking and credulity amounting to downright gullibility".


19th century revival

Zoologists working in the 19th century, including Georges Cuvier, Johannes Peter Müller, and Louis Agassiz admired Aristotle's biology and investigated some of his observations. D'Arcy Thompson translated ''History of Animals'' in 1910, making a classically-educated zoologist's informed attempt to identify the animals that Aristotle names, and to interpret and diagram his anatomical descriptions.
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist A biologist is a scientist who conducts research in biology Biology is the scientific study of life. It ...
quoted a passage from Aristotle's ''Physics'' II 8 in '' The 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". 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 discussing ontogeny, the Empedoclean coming into being of an individual from component parts, not
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree In botany, a tree is a perennial plant with an elongated ...
and
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism In biology ...
. 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."


20th and 21st century interest

Zoologists have frequently mocked Aristotle for errors and unverified secondhand reports. However, modern observation has confirmed one after another of his more surprising claims, including the active camouflage of the octopus and the ability of elephants to snorkel with their trunks while swimming. Aristotle remains largely unknown to modern scientists, though zoologists are perhaps most likely to mention him as "the father of biology"; the MarineBio Conservation Society notes that he identified " crustaceans, echinoderms, mollusks, and
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...
", that cetaceans are mammals, and that marine vertebrates could be either oviparous or viviparous, so he "is often referred to as the father of marine biology". The evolutionary zoologist Armand Leroi has taken an interest in Aristotle's biology. The concept of homology began with Aristotle, and the evolutionary developmental biologist Lewis I. Held commented that


Works

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 of ''The Anatomies'' are lost, but referred to in the ''History of Animals'', where the reader is instructed to look at the diagrams to understand how the animal parts described are arranged. Aristotle's main biological works are the five books sometimes grouped as ''On Animals'' (De Animalibus), namely, with the conventional abbreviations shown in parentheses: * ''History of Animals'', or ''Inquiries 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'' or ''On the Gait of Animals'' (De Incessu Animalium) (IA) together with '' On the Soul'' (De Anima) (DA). In addition, a group of seven short works, conventionally forming the '' Parva Naturalia'' ("Short treatises on Nature"), is also mainly biological: * '' Sense and Sensibilia'' (Sense) * '' On Memory'' * '' On Sleep'' * '' On Dreams'' * '' On Divination in Sleep'' * '' On Length and Shortness of Life'' * '' On Youth, Old Age, Life and Death, and Respiration''De Juventute et Senectute, De Vita et Morte, De Respiratione


Notes


References


Sources

* * * * * * * * * * {{Use dmy dates, date=April 2017 History of biology Philosophy of Aristotle History of zoology Ancient Greek science