Aristotle's biology is the theory of biology,
grounded in systematic observation and collection
of data, mainly zoological, embodied in Aristotle's
books on the science.
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's theory of Forms.
The theory describes five major biological
processes, namely metabolism, 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, 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, though Hellenistic medicine in Egypt
continued Aristotle's inquiry into the mechanisms
of the human body.
Aristotle's biology was influential in the
medieval 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
and William Harvey 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 (384–322 BC) studied at Plato's
Academy in Athens, remaining there for about
20 years.
Like Plato, he sought universals in his philosophy,
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 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, 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.
For example, the kind of animal called a bird
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 fishes within the fish kind.
He sometimes called these atoma eidē, indivisible
forms.
Human 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 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.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
control 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.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, not as we now think the brain.
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 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 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
– 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.
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 has fewer young (usually
just one) per brood than a mouse.
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 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 [sleep-making]
principle, 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,
toy carts, the movement of water through porous
pots, and even automatic puppets.
=== Complex causality ===
Readers of Aristotle have found the four causes
that he uses in his biological explanations
opaque, something not helped by many centuries
of confused exegesis.
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.
The efficient cause is how a system moves
and develops: to a modern biologist, those
are explained by developmental biology and
physiology.
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,
electric fish (Torpedo) and angler fish are
detailed, as is his writing on cephalopods
including the octopus, cuttlefish and paper
nautilus.
His claim that the octopus had a hectocotyl
arm which was perhaps used in sexual reproduction
was widely disbelieved, until its rediscovery
in the 19th century.
He separated the aquatic mammals from fish,
and knew that sharks 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 ruminants, 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).
Animals with blood included live-bearing tetrapods,
Zōiotoka tetrapoda (roughly, the mammals),
being warm, having four legs, and giving birth
to their young.
The cetaceans, 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
(reptiles and amphibians) had blood and four
legs, but were cold and laid eggs, so were
a distinct group.
The snakes, 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 cartilages instead of bones.Animals
without blood were divided into soft-shelled
Malakostraka (crabs, lobsters, and shrimps);
hard-shelled Ostrakoderma (gastropods and
bivalves); soft-bodied Malakia (cephalopods);
and divisible animals Entoma (insects, spiders,
scorpions, 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 (hot and dry); Air (hot
and wet); Water (cold and wet); and Earth
(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 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
turns to the weed darnel.
=== On Hellenistic medicine ===
After Theophrastus, though interest in Aristotle's
ideas survived, they were generally taken
unquestioningly.
It is not until the age of Alexandria under
the Ptolemies that advances in biology resumed.
The first medical teacher at Alexandria, Herophilus
of Chalcedon, corrected Aristotle, placing
intelligence in the brain, and connected the
nervous system 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 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 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
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 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 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.Darwin 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.
However, Aristotle immediately rejected the
possibility, and he was in any case discussing
ontogeny, the Empedoclean coming into being
of an individual from component parts, not
phylogeny and natural selection.
=== 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",
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
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.
== 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 (De Sensu et Sensibilibus)
(Sense)
On Memory (De Memoria et Reminiscentia)
On Sleep (De Somno et Vigilia)
On Dreams (De Insomniis)
On Divination in Sleep (De Divinatione per
Somnum)
On Length and Shortness of Life (De Longitudine
et Brevitate Vitae)
On Youth, Old Age, Life and Death, and Respiration
(De Juventute et Senectute, De Vita et Morte,
De Respiratione)
== Notes
