The History of Life: The Views of Aristotle and His Predecessors

By Dr. John S. Wilkins / 08.05.2016
Honorary Research Fellow
University of Melbourne

Nature versus Humanity

Before there was a literate, and philosophical, historical record, humans existed at least some 80,000 years. Around 12,500 years ago in the region surrounding Anatolia in modern Turkey, agriculture slowly began (the Neolithic Revolution, which spread across Eurasia over a period of some five thousand years or more), at first with the domestication of sheep, pigs and cattle, and then crops. This raises two questions:

  1. What was the default view of life by pre-agrarian humans? Did they see themselves as special among living things?
  2. What changes did the rise of agriculture bring about?

Now we have no record of unrecorded events, obviously, so we have to try to reconstruct the past by reference to the present, and this is, to put it mildly, difficult. Non-agrarian societies are known by anthropologists as “foraging” societies (they used to be called “hunter-gatherer” societies, but there was a clear gender bias in this – in fact the amount of food gotten through hunting is, in such societies we can observe, minimal compared to the gathering), and while we have studies of some such societies in the past couple of centuries, we have only physical remains of the pre-agrarian Indo-Europeans, and so we do not know much of what they thought. Anthropology is rife with projection onto the past to serve the agendas and prejudices of the present.

Consequently, we only have speculation, which frees me to speculate.

In the foraging societies we know today, living things are rarely distinguished from human beings. In some cases, members of other species are considered honorary humans for totemic (tribal symbolic) reasons. In other cases, human beings are considered honorary members of other species. There is reason to think that in the prehistoric ancient near east, human life was, like animal life, considered to be extinguished at death, and that the notion of a “soul” was not even metaphorically held . It seems there is no clear “default” view in foraging societies – which ought not to surprise us, as we have no reason to think that human culture was any the less complex in the past than now (technologies excepted).

One thing that is true of pre-agrarian existence is that foragers needed to understand the life-ways of their food species, both plant and animal. A forager that doesn’t know when a fruit or tuber is harvestable, or where a bird or other hunted animal lives or what it looks like, is a hungry forager. Experience of foragers in the modern era suggests they know the appearances, habits and habitats of their prey species as well or better than a modern biologist. However, if it isn’t hunted or gathered, they do no better than a suburban American. From this we may surmise that knowing the living world depends a lot upon what need we have for it.

Classification among foragers is generally fairly consistent with classification by biologists, excepting such cases as totemic animals and sacred species. In a famous paper, anthropologist Ralph Bulmer noted that among the New Guinea Highlanders, the cassowary (a flightless relative of the emu and the kiwi) was not classified as a bird, but afforded human rights and status (Bulmer 1967). The Karam do not hunt the cassowary, nor do they classify it among the birds, although their neighbours do. Similar attitudes occur among other foragers (Berlin 1973, Atran 1998).

But by and large, foragers, while never reaching the “in harmony with nature” myth of romanticism, do have a pretty decent handle on the objective biology they find around them. Did that change when humans became sedentary and started to live in towns and cities?

Some think so. One author believes that when cities evolved, martial necessities of walls to protect them (and thus to control the viable land surrounding them) made the inhabitants start to see civilised living as distinct from wilderness, and so to see humans as separate from the rest of the living world. I rather doubt this happened, if it did, in such a sudden fashion, but it seems reasonable that humans started to see themselves as separate to, or above, nature in the early period of civilisation (that is, the invention of city states), as we see it in several archaic myths, such as the Arcadia mythology of the Romans, yearning for a rural (that is, agricultural, not wild) past.

In fact, wilderness was less an idyllic scene to the early civilisations than it was something to be beaten back and feared, as farming was the source of civil wealth, not forests. The shift from the “riches of the forest” shared by foragers to the ownership by elites of the land on which farming and animal husbandry took place is crucial to understanding how the living world was seen after the Neolithic Revolution.

Every civilisation needed to understand basic facts about the animals and plants they farmed, so it is not surprising that societies like the Indus Valley, Mesopotamian cities, East Asian cultures and so forth all had extensive classifications of animals and plants, and understood a fair bit about anatomy and physiology. However, there is little to no evidence, Hindu apologists and similar movements aside, that the living world was the subject of a sustained and careful investigation in these areas. This is not to say that there were none, but only that the evidence does not survive if there were. Where there was, it was in the Hellenic civilisation of around the sixth century BCE.


Atran, S. (1998). “Folk biology and the anthropology of science: cognitive universals and the cultural particulars.” Behavioral and Brain Sciences 21(4): 547–609.

Berlin, B. (1973). “Folk Systematics in Relation to Biological Classification and Nomenclature.” Annual Review of Ecology and Systematics 4(1): 259-271.

Bulmer, R. (1967). “Why is the cassowary not a bird? A problem among the Karam of the New Guinea highlands.” Journal of the Royal Anthropological Institute 2(1): 5-25.

The Milesians and Monism

Normally in the history of philosophy the earliest Greek thinkers are referred to as “pre-Socratics”, but in biology, the first systematic thinker is Aristotle, so here we look at his predecessors.

One of the issues in histories of ideas is that one can find precursors for nearly every idea you like. Back in the 1890s, a neo-Lamarckian palaeontologist seeking to deprecate the originality of Darwin, Henry Fairfield Osborn, wrote a book From the Greeks to Darwin in which he found evidence among the pre-Aristotelians of evolution and natural selection. A similar issue appeared when Darwin was accused of not giving credit to his predecessors by Lamarckians and others, resulting in the Historical Sketch in the third edition of the Origin and subsequent editions. We shall address this as we go, but I must note that these thinkers were not, primarily, naturalists or natural historians (as biology and geology were known prior to the nineteenth century), and they thought about a great many other things. We choose these thinkers just because of their influence on later biological thinkers and naturalists. It pays to be careful when we do this, because we can end up with the impression that history has a definite lineal nature, when in fact it, like evolution itself, is a process of branching, extinction and repetition.

Prior to these thinkers, so far as is recorded, explanations of things like seasons, generation (a word that roughly means development in modern terms), and the existence of organisms were given in religious stories, and consequently had little to no predictive power. Gods do things for their own reasons, and these stories, like the Enuma Elish or Bereshit (Genesis, which consists of several traditions of Hebrew thinking), or the Greek Hesiod in his Works and Days, tended to be focused upon giving an account of the right relations between gods and humanity, rather than passing on knowledge of living things. In short, explanations boiled down to the whims of the gods.

The first (known) thinker to reject this was a Hellene in what is now Turkey, Thales of Miletus in the sixth century before the Common Era (flourishing around 585 BCE). Thales held that things had their own natures based upon an underlying nature (which he identified as water). The properties of the basic stuff determined in a regular manner the way things behaved, and so explanations should be sought in terms of this underlying stuff. Such a position is called now monism, because there was a single (monos) cause of the order of things (kosmos). Thales was thus the first western materialist.

He was not the first materialist though. A school that preceded the Vedic traditions in the Indus Valley was also materialist: the Lokayata or Carvakist schools which began in the eighth century BCE. They held that matter precedes consciousness, and that the soul did not survive death, and they also were strongly empiricist. I sometimes think that given the extensive trade from India through Persia and thence to Greece, that a number of philosophical ideas in the Hellenic world were borrowed from, or influenced by, the Indian thinkers.

Thales’ views created a school known as the Milesian school, with Anaximander (fl. 550) arguing that the single cause was the apeiron (something like stuff of unbounded possibility), and Anaximenes that it was air, which when denser caused earth and rocks to come into being, and when less dense, fire. What is significant about these early views is that at no point in their accounts of natural processes did they invoke the gods.

The basic reason why such accounts were necessary had to do with the question of knowledge. If knowledge is possible about the world, there must be some invariant stuff that makes it possible to know. If one could explain all things as rearrangements of some property-bearing stuff (which came to be called substance, or that which stands under, in the Latinate tradition of a few centuries later), then knowing what the properties of the stuff itself was meant one had a complete (in principle, anyway) explanation of why physical things did what they did. Shortly after the Milesians came the atomists, which believed that all things were made from rearrangements of eternal and indivisible (atomos) small particles of varyings sizes and shapes.

So far we have nothing much to do with life, though. But one Milesian – Anaximander, did produce a kind of theory both of the origins and the generation of living things. There are only a few reports of his views:

“Anaximander says that the first animals were produced in moisture, enclosed in thorny barks. When their age increased they came out into the drier part, their bark broke off, and they lived a different mode of life for a short time.” Aetius (5.19.4)

“He also declares that in the beginning humans were born from other kinds of animals, since other animals quickly manage on their own, and humans alone require lengthy nursing. For this reason, in the beginning they would not have been preserved if they had been like this.” Pseudo-Plutarch, Miscellanies (179.2)

“Anaximander… believed that there arose from heated water and earth either fish or animals very like fish. In these humans grew and were kept inside as embryos up to puberty. Then finally they burst and men and women came forth already able to nourish themselves.” Censorinus, On the Day of Birth (4.7)

This has been (for example by Osborn) interpreted as an evolutionary account. Instead, it is better to see this as being spontaneous generation – living things arising out of pre-existing non-living matter due to the drying of the waters,, and then humans forming within fishlike beings until they could survive on their own. Confusion between spontaneous generation (we would now call it origins of life, or as I prefer, etiobiology) and evolution (the changes over long periods of time of organisms) continues even today, and this simply is not about the gradual changes of one kind of organism to another, let alone one of relatedness of species.

Moreover, the function of these speculations is to shore up the underlying metaphysics of their monism, rather than to investigate the living world. At this stage we do not have much in the way of a biological tradition.

The Eleatics and the Atomists

I will be passing over many philosophers, such as Heraclitus (“everything flows”) only because they said nothing of great influence directly on biology. As we shall see when we finally get to the modern era, this doesn’t mean that some philosophers like Whitehead or Teilhard didn’t draw biological conclusions from them. For perhaps the most detailed, if somewhat obscure, history of philosophy see Windelband 1901, and for the period up until Leibniz, Russell 1946 (after that he gets a bit partisan).

Most histories of biology introduce the pre-Socratics in greater detail than necessary for just biology (e.g., Singer 1931, cp Magner 1994). This seems to be a hangover of older educational expectations and assumptions (that we all know about pre-Socratic philosophy in culture and school).

One source that readers may be surprised that I am not using much here is Ernst Mayr’s The Growth of Biological Thought (1982). There are two reasons for this. One is that Mayr is not reporting much new in that book, and often repeats older mistakes; the other is (see the prelude to this series) he is unashamedly Whiggist, seeing all biology leading up to (his version of) Darwinism. Caveat lector.

The soul

Before we continue, a note on the term psyche, which is often translated as “soul”. Due to our Christianised lens, we tend to think of this as some kind of immaterial substance separate from the physical world. This is a (very) late reinterpretation. Initially, and especially in the early period of Greek thinking, psyche means something like “a mover”, analogically to the wind that “blows” (the original meaning of psyche). As the idea of this motive force was discussed, it came to be thought of as that which departs at death, or survives death, and so came to be known as the “life force” in modern New Age terms. However, the early “biologists” (hey, if a Greek thinker can’t be called a biologist, who can? The very word is Greek) sought to account for life in various ways, from heat, moisture, and other elements.

When we get to Aristotle, this will become clearer, but it’s important that the history is understood to be a series of explanations for psyche rather than there being some generic Greek idea of psyche. Societies do not in general have universally shared ideas or interpretations of words.

The Eleatics

In contrast to the Milesians, a school of thought called the Eleatics held that knowledge through the senses is misleading, although some (for example the founder of the school, Xenophanes) held that it approximates knowledge “by degrees” (an early version of Bayes?). They therefore did not engage in a study of the natural world either. The Eleatics were based at the residence of Xenophanes of Kolophon, Elea, in Salerno, southern Italy. Ela was a Hellenic colony. Xenophanes was born around 580 BCE in Asia Minor (modern Turkey), and after wandering for a time settled there and began writing poems.

One of them came later to be known as On Nature (peri phuseos in Greek – a number of books were given that title by later scribes and editors), and in this book/poem, which is mostly lost to us apart from some excerpts in other preserved classical authors, he made some claims, based on his physics, about life and its history.

The Eleatics generally held that truth is eternal, and as a consequence, sensory information is misleading – they were idealists, in our terms. However, Xenophanes did think that the primordial element was earth*, which on being compressed from a fluid to solidity, trapped sea shelled animals in mountains, which had once been under the sea. This account of fossilised shells did not become widely adopted before the 17th century when Nicholas Steno proposed it, despite a number of classical and non-European precursors.

Xenophanes argued that religions were human projections, and that other animals would draw gods in their own image. As part of his doctrine that there is only one nature, and all else is mere appearance, he also held that the true deity would be so perfect and abstract that we could not describe it.

Parmenides of Elea apparently held some views on conception and reproduction. There are four fragments of his poem (also later called On Nature):

Fragment 16

For as on each occasion a blending (mingling) holds of much-wandering limbs, so noos is present to humans; for the nature (form) of limbs is the same thing that thinks (apprehends: phroneei) in humans (OR:…is the same thing that is thought (apprehended) in (of, for) humans) both for all together and individually; for the full is conceived (no?ma) [of]. (OR:…is what is conceived [of].)

Here Parmenides proposes a widely held view until the nineteenth century known later as “pangenesis”, in which the organs of the body shed parts that are recombined in sex (and draws the analogy with mind here).

Fragment 17

Boys to the right, girls to the left

This was read by later classical authors (e.g., Aristotle) to mean that boys are conceived on the right side of the uterus and girls on the left side.

Fragment 18

When woman and man [together] mix the seeds of Venus (Love), the power which forms [bodies] (OR:the power which is formed) out of the different blood, if it maintains proper proportion, produces well-formed (well-constituted) bodies. For if the powers, when the seeds are [being] mixed, fight and do not constitute (make) a unity in the body in which the mixture has taken place, then they will terribly (cruelly) torment the nascent (growing) sex with double seed.

The notion, critical in subsequent debates, that proper generation requires balance or harmony of parts and elements, is expressed here.

Overall, the Eleatics tended to use biological examples and explanations as outworking of their metaphysics, and not for their own value.

The Pythagoreans

While Pythagoras himself, perhaps the singularly most influential thinker of the sixth century BCE in Hellene, is not recorded saying much about the living world (which, like everything else he thought to be comprised of numbers), one of his likely students, Alcmaeon, is the first recorded Greek philosopher to carry out direct dissections of animals to learn abut their natures. He may also have studied the development of chicken embryos. He discovered the optic nerve, the (later named) Eustachian tube, and declared that understanding was the only qualitative difference between humans and the other animals. Whether he did or not is debated, as is whether he was actually a Pythagorean. However, he was likely a physician, and his experience in that field may have led him to critical observation, however, primitive from our perspective, as it did the Hippocratic school.

Pythagoreanism did not, so far as we are aware, offer a theory of life other than moral and psychological accounts of sensation.

The Atomists

The Greek focus on permanence and unchanging properties as an explanation for knowledge led to the atomists, who held that underlying all change and different bodies there were elemental particles that had inherent properties. Atomists hypothesised that these particles were indivisible, the Greek for which is atomon. In the 5th century BCE, Leucippus, following the argument of the Eleatic Parmenides, had accepted that change was not possible unless there was a vacuum (non-being) and so he proposed that atoms existed in a vacuum.

His follower Democritus expanded on this view, and proposed an element (possibly fire) that gave living things their growth and movement (their psyche). He also seems to have given an account of generation (as reported by Aristotle and Aetius):

Democritus of Abdera also says that the differentiation of sex takes place within the mother; that however it is not because of heat and cold that one embryo becomes female and another male, but that it depends on the question which parent it is whose semen prevails — not the whole of the semen, but that which has come from the part by which male and female differ from one another. [Aristotle, On the generation of animals, 764a.7ff]

The significance of the atomists’ ideas lies largely in the reaction (quite a strong one by Plato and Aristotle; Plato wished to burn all atomists’ works, by one account) against mechanistic explanations, and Aristotle’s views, based on Empedocles’ view of elements, coloured biology for about two millennia.

* Or perhaps earth and water. The sources are unclear.


Magner, L. N. (1994). A history of the life sciences. New York, Marcel Dekker, Inc.

Mayr, E. (1982). The growth of biological thought: diversity, evolution, and inheritance. Cambridge MA, The Belknap Press of Harvard University Press.

Russell, B. (1946). History of Western philosophy and its connection with political and social circumstances from the earliest times to the present day. London, George Allen and Unwin.

Singer, C. J. (1950). A history of biology to about the year 1900: A general introduction to the study of living things. London, Abelard-Schuman.

Windelband, W. (1901). A history of philosophy: with especial reference to the formation and development of its problems and conceptions. New York, Macmillan.

The Four Elements

The Four Elements (Empedocles)

Empedocles (ca. 495–435 BCE), who lived in Sicily, was influenced both by the Pythagoreans and Parmenides (in his poem “On Nature”) and proposed what came to be called the “four elements” theory to explain why there was change if the universe was monistic. It was just recombination of eternal and unchanging elements (he called them “roots” [rhizomata]; later Plato named them stoicheae, from which we get stoichiometric chemistry). This was not unique to Greece. Similar schemes existed in Babylonian mythology, in Hindu thought, in Chinese thought (they had five elements which were not eternal, but transitional phases of matter) and in Japan. It is not clear if Empedocles came to this view directly (through observing that air prevented water from entering a pipette-like clepsydra, or water clock) or was influenced by eastern ideas.

The four elements or roots of being were the familiar list – earth, air, fire and water. Each element had properties that when mixed in anything (including living things) gave the whole its properties. But what caused the change itself? Empedocles thought that the universe had two opposing forces which he called Love and Hate, and which a modern might call less directly analogically, attraction and repulsion (which terms mean literally, love and hate). He has been criticised a lot for his anthropomorphism for this; and some does occur, but he’s no more guilty of it than a Newtonian physicist.

The doctrine of the four elements became, following Aristotle and Galen, the standard foundation for physics, medicine and biology for the next 22 centuries or so.

The Hippocratic School

Hippocrates of Kos (460–ca. 377 BCE) founded a school of medicine in Thessaly, and was regarded (according to Plato) as the leading physician of his time. His school focused on observation rather than theory, but he adopted the Emepdoclean view that illness was caused by an imbalance of these elements, which in the body were humors: black bile, or melancholy (element: earth), yellow bile, or chole (element: fire), blood (sanguis, element: air), and phlegm (element: water). From these came the four temperaments, melancholic, choleric, sanguine, and phlegmatic, each caused by a dominance of one of these humours. This view was later taken up by the Roman 2nd century CE physician Galen.

The observational aspect of Hippocratic epistemology was, surprisingly, approved of by Plato. However, Hippocrates is reputed to have argued that thoughts originated in the brain, a view that neither Plato nor Aristotle followed:

Men ought to know that from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears. Through it, in particular, we think, see, hear, and distinguish the ugly from the beautiful, the bad from the good, the pleasant from the unpleasant, in some cases using custom as a test, in others perceiving them from their utility. It is the same thing which makes us mad or delirious, inspires us with dread and fear, whether by night or by day, brings sleeplessness, inopportune mistakes, aimless anxieties, absent-mindedness, and acts that are contrary to habit. These things that we suffer all come from the brain, when it is not healthy, but becomes abnormally hot, cold, moist, or dry, or suffers any other unnatural affection to which it was not accustomed. Madness comes from its moistness. When the brain is abnormally moist, of necessity it moves, and when it moves neither sight nor hearing are still, but we see or hear now one thing and now another, and the tongue speaks in accordance with the things seen and heard on any occasion. But all the time the brain is still a man is intelligent. … Wherefore I assert that the brain is the interpreter of consciousness.*  [On the Sacred Disease, Loeb edition, pp177-179]

He also famously held that epilepsy, and by implication all disease, was caused by failures of the body and not the actions of gods or prophetic power:

It is not, in my opinion, any more divine or more sacred than other diseases, but has a natural cause, and its supposed divine origin is due to men’s inexperience, and to their wonder at its peculiar character. Now while men continue to believe in its divine origin because they are at a loss to understand it, they really disprove its divinity by the facile method of healing which they adopt, consisting as it does of purifications and incantations. But if it is to be considered divine just because it is wonderful, there will be not one sacred disease but many, for I will show that other diseases are no less wonderful and portentous, and yet nobody considers them sacred. For instance, quotidian fevers, tertians and quartans seem to me to be no less sacred and god-sent than this disease, but nobody wonders at them.  [On the Sacred Disease, Loeb edition, pp 139-141]

This demythologising of disease had a massive influence on subsequent medicine, and biology.

The four elements/humors scheme as it developed can be (and was often) diagrammed:

The ratio of these humors determines the health of the organism, and when each organ has the right proportion – is not too hot, cold, wet or dry – then it is as it ought to be. This view was accepted and promoted by Aristotle and Galen.

Although this scheme was intended to be an account of both the properties of the body and of changes to it, another way in which it functioned (and continued to for most of two millennia) was as an ars memoria – art of memory technique. Like the Pythagorean ratios, the scheme allowed the learner to slot different things in the diagram so they could be easily remembered. In the later middle ages, this became the Kabbalah as well as esoteric knowledge of scholarly and mystical arts.

* Or “interprets the understanding” (hermeneuonta ton sunesin).

Aristotle’s Underlying Philosophy

Plato’s pupil, and later Alexander the Great’s tutor, Aristotle was born in Stagira in Macedonia in 384 BCE (died 322 BCE), and is sometimes known as the “Stagirite” in older writings. His activity was mostly in Athens, where he studied with Plato, and where he set up a school after Plato’s death, where he and his students would walk and talk in the shaded walks around the gymnasium known as the Lyceum. His school is thus called the “Peripatetics” (“those who walk from place to place”).

Aristotle’s works are divided into

  • the logical (the Organon, including the Posterior Analytics and the Categories – see below),
  • the metaphysical (the term “metaphysics” itself possibly comes from the position of his works under that title in the order of later bindings – it came after (meta) the Physics),
  • the physical (including the works involving biology),
  • the psychological (including On the Soul, or De Anima),
  • the ethical and
  • several contentious works under his name dealing with poetry and rhetoric.

The works that apply to his very influential ideas on life, and natural history are often called the Liber Animalium (Book of Animals), but which includes three books (known in their Latin titles: Historia Animalium, De Generatione Animalium, and some minor works like De Locomotio Animalium and so on).

Aristotle’s biological ideas are founded firmly on his theoretical philosophy and physics, and so before we get into his works on life (including human nature) we have to understand some of his teachings. It is important to know that he considered the study of the natural world to be natural philosophy and the study of the terrestrial (including the living) world came to be known as natural history after his book Historia Animalium, as historia in Greek originally meant “investigations”.

Unlike Plato, Aristotle believed that the foundation of knowledge was experience. He considered logical issues were important, however, so that we could explain why things (like humans lacking tails, to use James Lennox’s example, 2001, p 13) had characters they did because they were part of a larger class of things that had those characters (in this case, hominoid apes, which lack tails). Knowing the class, which he referred to as genera (sing. genus) allowed us to understand the properties of a member of that genus.

A genus is like a set (not coincidentally, since the Aristotelian categories informed modern set theory). Genera can include individual things, like John Wilkins, or subgenera like Australians. A subgenus is a species of that genus (and no species is properly a member of more than one genus in what Aristotle considers a well-formed classification). However, unlike the modern Linnaean taxonomic scheme, a species can also be a genus of something else, and have its own subgenera or individual members.

As we shall see when we come to his biology, Aristotle did not always use the Greek terms genos (Latin: genus) or eidos (Latin: species) when discussing living kinds. However, the terms of his logic (in the Posterior Analytics, for example) were in the first instance applied to terms (“predicates” via Latin, translating the Greek katēgorēma, from which we get “category”). In short, this was explanation in terms of words. And this was entirely proper for the explication of logic. However, it is not how he undertook his natural history, as we shall see.

Aristotle also had a theory of categories (in the Categories, appropriately enough), which was an a priori classification of being. There were things that were accidental, and things which were essential. There were also things that were “universals” (katholou, a portmanteau word meaning initially “according to the whole”; we might use the world “class” to express it today) and things which were particulars (individual things). This gives us four combinations (a number Aristotle was very fond of):

  • accidental universals,
  • accidental particulars,
  • essential universals and
  • essential particulars.

“Essential” here means “what it is to be” something (literally, in the Greek). So we speak of things as being accidentally or essentially particulars or universals. This is relevant to his treatment of classification and definitions of living things.

Aristotle’s theory of physics included the Empedoclean four-elements theory. He held that there were two contraries: hot-cold and wet-dry. Each element was a mixture of these properties. There was also a fifth element, later called the ether (aither) which the heavens, which did not corrupt or change, was made of. The heavens began at the lunar sphere, and generation and corruption (coming to be and passing away) only occurred in the sublunary realm, which included the earth. Aristotle offered up a “two sphere” universe:

The Aristotelian two-sphere cosmology as drawn by Peter Apian in 1524.

The earth was at the centre of the universe and the planets sat on crystal spheres. The outer shell was the sphere on which the fixed stars were, well, fixed. Change in the heavens was circular and eternal, as Plato had thought, while change in the sublunary realm was temporary. Later Christian theologians added God’s habitat, heaven, outside the fixed sphere.

Terrestrial things were composed of mixtures of the four elements, and a surplus or deficit of them from the normal (“proper”) balance caused all kinds of difficulties such as illness or deformed animals, including humans.


The best introduction to Aristotle’s philosophy of biology is

Lennox, J. G. (2001). Aristotle’s philosophy of biology: studies in the origins of life science. Cambridge, UK; New York, Cambridge University Press.

Aristotle’s Explanations


Aristotle is (in)famous for his four causes, although they are better thought of as types of explanations. They are usually given standard names, but to make them a bit clearer, I’ll give some simpler  names first (just as Aristotle did in Greek).

  • Composed-of (the material cause): the properties something has due to the material it is made of;
  • Form-of (the formal cause): the properties something has in virtue of its shape;
  • Moved-by (the efficient cause): the properties it has from some external force;
  • Purpose-of: (the final cause): The reason something exists for.

Now the last one, the final cause, is a bit odd to modern eyes. It is not a cause in the sense we understand it, because unless causes can operate from future to past, the purpose of something is not what makes it be what it is, unless prior to the thing existing someone intended it to be for the purpose. An example might help confused modern readers.

Supposed we have two wheels made out of different materials, brass and wood. The weight and strength of the two wheels clearly is due to the stuff they are made of. That is a material cause. They both roll because of their shape. That is a formal cause. What makes the wheels roll rather than stand still is the efficient cause (in Aristotle’s physics, things do not move if they are in their natural place, and so they need something to move them). And the craftsman who made the wheels had a purpose for making them, which is the final cause.

To our eyes this is strange. The key confusing term here is “cause”, which in Greek is aition. It comes from a root word that means “fault” or “culpability”. Aristotle (and his predecessors) ask what is the culpability of some property. It has been suggested that the better English equivalent is “account”. In this interpretation, his “causes” are logical accounts of the properties of the object (the technical term for logic in Aristotle is “syllogistic”).

This puts a different spin on Aristotle’s notion of causation. Since the final cause in particular plays a large role in biology (the “function” or purpose of living parts, for example), it is important to note this. Later, with the rise of early modern science in the 16th century, final causes became contentious, although they remained in biology for much longer, being called teleology.

Form and Substance

Aristotle also has a physics that plays on the first two accounts, the material and the formal. He opposed atomism and the existence of a void* between them. All space must be filled by a substance, and upon that substance a form is imposed so that it has the properties it has. This view, the substance/form division, is called hylomorphism. It was the ruling physics of the west until the development of modern atomism by John Dalton in the 1800s. Aristotle uses this notion to explain much of biology, including the mind.

In Aristotle’s metaphysics, form (morphē) explains the external properties of things like organisms. It is imposed upon the substance and does not, unlike Plato’s Forms, exist independently of them. The “soul” (psuchē) is a form that moves organisms, and the mind’s form (nous) is the soul that permits reasoning. Aristotle has form and matter (substance in Latin) as a single unity of being (ousia). The shape of wax is not separable from the substance wax, for example. When a thing changes, what changes is its form.

This leads to Aristotle’s tripartite distinction of souls in De Anima (On the Soul, follow link for a short discussion). There are three things that living bodies do which is proper to them:

  • Grow by way of taking in nutrition
  • Move and perceive things
  • Think or have intellect.

This gives living things three possible souls:

  • The Nutritive soul (all living things have this; plants have only this)
  • The Sensitive or Locomotive soul (all animals have this); sometimes the “Appetitive soul” is added in here or treated as separate.
  • The Rational soul (only humans have this).
This led to a long-lasting (even today) distinction between “lower” forms of life and “higher” forms of life that came to be known as the Great Chain of Being. We shall cover this much later. As reconstructed by later writers, Aristotle’s view can be diagrammed like this:
From Charles Singer, A Short History of Biology.

One interesting thing about this is that it does not form a single linear arrangement of life, in contrast to later forms of the Great Chain. There are numerous things that exist in the nutritive “layer”. The other thing to note is that this is not divided sharply into genera or classes. It is a continuum, and the least complex things arise out of matter in what came to be known as spontaneous generation, which we shall encounter again later.


∗ The phrase “nature abhors a vacuum” is much later, due to Rabelais in the 1530s.

† In Aristotle’s scheme, something can be proper or accidental. A proper feature is one that cannot be removed without the thing ceasing to be that kind of thing. An accidental feature can be removed and the thing remain that kind of thing. So a bird properly has a beak or bill, but accidentally has the colour white.