The ‘prehistory’ of philosophy of science (7): The invention of biology

During the time Aristotle spent far from Athens after the death of Plato, he lived for a few years on the island of Lesbos and in some Asia Minor cities that surrounded it, an area where a kind of ‘franchise’ of the Academy had been founded a few years ago under the patronage of the tyrant Hermias of Atarneus, who became one of the dearest friends of Aristotle (until his torture and crucifixion by the Persian king in 341 BC), and with whose niece Pythias the philosopher became lovingly married. Pythias, as well as one young student from Lesbos, named Tyrtamus (and that Aristotle renamed as ‘Theophrastus’: ‘of Divine Speech’), became his closest collaborators in the next years, though Pythias died relatively soon, nearly after Aristotle’s return to Athens in 335, whereas Theophrastus survived him for almost 35 years as his successor in charge of the Lyceum.

Landsat image of Lesbos. Source: NASA

Aristotle’s interest in the living beings had surely started during his stay in Plato’s Academy, but it was probably in Lesbos when, far from the contact with other scholars more immersed in abstract and metaphysical discussions, he concentrated most of his intellectual activity into the direct study of animals, starting the immense work that now occupies more than one half of all of his preserved writings. Lesbos, in particular, has a couple of almost closed big lagoons (or albuferas) 1 , the gulf of Kallonis and the gulf of Teras, where life thrives, and where fishers could be constantly providing him with both specimens and experiences (empeiríai, what –we must recall– he placed just in the middle of his ladder of knowledge, between the extremes of ‘perception’ and ‘science’). Scientific knowledge, for Aristotle, comprised two essential elements: knowing-what, and knowing-why. Of course, the second was for him the most excellent, but, he thought, it was worthless to speculate on the ‘whys’ without the most possibly detailed knowledge of the ‘whats’, and life offered, once a philosopher started to go to the trouble of looking deeply into it, an infinite variety of wonders to discover. Aristotle might have considered that, if we want to understand the world (which was the main goal of philosophy), we must particularly fix our attention in the most wonderful and complex part of nature, the living beings, rather than in more abstract and ‘simple’ entities (like those of mathematics and astronomy, not to speak of ‘the elements’), that had fascinated Plato and most other philosophers before him.

Hence, Aristotle started to elaborate a kind of work that his teacher would surely had considered boring and uninstructive, not to say vulgar: a meticulous catalogue of the peculiarities of animals, their parts and their kinds, the working of their organs and of their reproduction, their habits, their differences, and their similarities. Not all of this work has survived (for example, an impressive collection of anatomic charts and diagrams, accompanying the written text of other treatises, and very likely produced with the help of his wife, Pythias, was probably lost before the end of the Ancient times), but his books, known to the Christian civilisation by their Latin titles Historia animalium, De partibus animalium, De motu animalium, De generatione animalium, etc., became the main source of zoological knowledge for the following two millennia, and were praised as profound masterpieces even by Darwin himself. Of course, this knowledge-of-the-what-kind about animals can only be obtained by very different methods that knowledge about triangles, stars, or ideas of justice: one can’t avoid but getting ‘dirty hands’, for not only ‘field observation’, but systematic dissection, and even vivisection, had to be carried out by Aristotle and his collaborators, in order to grasp what was there, and what happened, within those complex things animals are. In one vivid example, something we might consider as the first ‘controlled experiment’ in the history of science is reported by Aristotle: the vivisection of chicken eggs after one, two, three days… till their eclosion in the 21st day, in order to observe and register the development of the embryo.

One fundamental thing Aristotle verified when studying the animals was that, in spite of being very different, their variety seems to be arranged in a kind of hierarchical organisation, one that allows to describe ‘genera’ of bigger or smaller ‘generality’, from the most encompassing ‘kingdoms’ (to use a much more modern term), to the most differentiated ‘species’ (a concept, instead, that he didn’t only employ –of course, in his Greek tongue: éidos–, but that had been used by Plato as one of the names he used to refer to his eternal ‘Forms’, or ‘essences’). And, more importantly, this classification was not merely ‘logical’, or ‘arbitrary’ (in the sense that we may order and classify a set of things according to whatever list of properties they have), but something inscribed into the very nature of the things, making some groupings ‘natural’, and other ‘artificial’. For example, both humans and ducks are ‘bipeds’, contrarily to foxes, but humans belong into a natural group with foxes (the group Aristotle called ‘viviparous tetrapods’), whereas ‘bipeds’ is a category lacking biological relevance as for the most natural classification of the animals. Hence, some features and similarities between different animals are more important than others, ‘biologically speaking’, because they are more directly related to the essence of each species; and so, an adequate science of the animals has to start not only by a ‘rational’ classification (some derived from a merely speculative play of ideas), but with a detailed observation and comparison of their characteristics that leads to a natural ordering. The science of nature begins, hence, by ‘carving nature at its joints’ (an expression that, in fact, comes from Plato’s Phaedrus).

By the way, Theophrastus, who focused his own scientific research on plants and minerals, confirmed later with some discomfort that a ‘natural classification’ was much harder to find outside of the animal kingdom, especially in the case of ‘rocks’. Both he and Aristotle didn’t suspect, obviously, of the essential role that genetic inheritance and evolutionary processes had in the creation and in the distinctness of biological kinds. Theophrastus was also a little bit sceptical (though not too much) on his teacher’s main idea about what is what grounds the ‘naturalness’ of natural classifications. Remember that, for Aristotle, scientific knowledge consisted basically in knowing-why, or knowing something’s causes. He is also famous for his theory of ‘the fourth (types) of causes’, i.e., four ‘avenues of explanation’ we might give of a fact: the material (what is something ‘made of’), the formal (what its ‘structure’ is), the agential (who ‘did’ it), and the final cause (what is the purpose of the process), but, following the vision of Plato, Aristotle gave supreme importance to the latter type of explanation: “nature does nothing in vain”, he wrote repeatedly; all aspects of the world, and in particular, all the features of animals, should be ultimately explained by their function. Of course, living beings are (outside artifacts) the paradigmatic type of entities where parts are best understood by their contribution to the ‘working’ of the whole, and hence, where teleological explanation is most useful; actually, the word ‘organon’ (in Greek, ‘instrument’) was given by Aristotle its technical, biological meaning of ‘body part’ that now is prevalent. Instead, the old Theophrastus ended recognising that some features of living beings have probably no function at all (for example, males nipples), and much more examples outside biology (tides, to mention just one), and hence other forms of explanation should be pursued in these cases.

I shall lastly mention that, even if ‘biology’ is his dearest intellectual child, Aristotle, as his master Plato before him, thought the duty of a philosopher was to offer a scientific ‘theory of everything’, and hence his vision of natural science was essentially connected to a global understanding of the world and of science in general, and it is this connection what we shall examine in the following entry.


  1. Leroi, Armand Marie. The Lagoon: How Aristotle Invented Science. London: Bloomsbury, 2014.

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