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In today's taxonomy animals, plants and other organisms are organized in species. Defining a species is no simple task for modern biologists, but we have a fair understanding of what a species typically means. In case of sexual reproduction, a species is defined by means of ability to produce fertile offsprings. There are many different groups of species, like genus, family and kingdom.

Did the Romans — or other ancients, for that matter — have any definition of a species? Was it just an intuitive sense of similarity, or did someone tell what they mean by a species, genus, or other taxonomic group? In other words, did the Romans have any taxonomic definitions? Any Latin passage from the antiquity discussing this matter would be great.

Wikipedia is quite vague and lacks citations on the early history of the concept of a species:

In the earliest works of science, a species was simply an individual organism that represented a group of similar or nearly identical organisms. No other relationships beyond that group were implied. Aristotle used the words genus and species to mean generic and specific categories. Aristotle and other pre-Darwinian scientists took the species to be distinct and unchanging, with an "essence", like the chemical elements.

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    Thomas of Aquinas, based in Aristotle, writes in extenso about species and their members. He uses species, -ei. A closely related term is natura, -ae, which comprises what is proper to individuals of a species for belonging to that species (as in human nature). I might be oversimplifying. I wish I had the time to do some research and write a proper answer (which I haven't) – Rafael Nov 7 '16 at 20:01
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    Also related: forma, and genus. Look at L&S's entry for species, meaning II.C.3 – Rafael Nov 7 '16 at 20:11
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    @Rafael, Aquinas is later than what I'm looking for, but his discussion and commentary on Aristotle's view would be interesting. I imagine someone would have looked into it in the Roman antiquity, too. I hope your findings help someone write an answer. – Joonas Ilmavirta Nov 7 '16 at 20:19
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    The cited wiki-nonsense seems to claim that Aristotle wrote in Latin. – fdb Nov 8 '16 at 18:05
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    @fdb, it indeed does so. That was one of the reasons I did not want to trust it. – Joonas Ilmavirta Nov 8 '16 at 18:08
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As Aristotle is generally considered as the father of biology — Darwin wrote: “Linnaeus and Cuvier have been my two gods… but they were mere school-boys to old Aristotle.” (in a letter to W. Ogle, 1882) —, it is logical to search for such a definition in his works.

According to Pierre Pellegrin (in particular in Une zoologie sans espèce, 1984), the definition isn’t the goal of Aristotle’s biology, however we can note two passages:

  • where Aristotle defines the genus by the resemblance:

    (PA, 645a {{fr}}) […] Σχεδὸν δὲ τοῖς σχήμασι τῶν μορίων καὶ τοῦ σώματος ὅλου, ἐὰν ὁμοιότητα ἔχωσιν, ὥρισται τὰ γένη, οἷον τὸ τῶν ὀρνίθων γένος πρὸς αὐτὰ πέπονθε καὶ τὸ τῶν ἰχθύων καὶ τὰ μαλάκιά τε καὶ τὰ ὄστρεια. Τὰ γὰρ μόρια διαφέρουσι τούτων οὐ τῇ ἀνάλογον ὁμοιότητι, οἷον ἐν ἀνθρώπῳ καὶ ἰχθύϊ πέπονθεν ὀστοῦν πρὸς ἄκανθαν, ἀλλὰ μᾶλλον τοῖς σωματικοῖς πάθεσιν, οἷον μεγέθει μικρότητι, μαλακότητι σκληρότητι, λειότητι τραχύτητι καὶ τοῖς τοιούτοις, ὅλως δὲ τῷ μᾶλλον καὶ ἧττον.

    Translation (W. Ogle):
    It is generally similarity in the shape of particular organs, or of the whole body, that has determined the formation of the larger groups. It is in virtue of such a similarity that Birds, Fishes, Cephalopoda, and Testacea have been made to form each a separate class. For within the limits of each such class, the parts do not differ in that they have no nearer resemblance than that of analogy-such as exists between the bone of man and the spine of fish-but differ merely in respect of such corporeal conditions as largeness smallness, softness hardness, smoothness roughness, and other similar oppositions, or, in one word, in respect of degree.

  • and where he proposes a determination of species from a combination of parties:

    (Politics, 1290b25-37 {{en}}) […] [25] ὥσπερ οὖν εἰ ζῴου προῃρούμεθα λαβεῖν εἴδη, πρῶτον ἂν ἀποδιωρίζομεν ἅπερ ἀναγκαῖον πᾶν ἔχειν ζῷον (οἷον ἔνιά τε τῶν αἰσθητηρίων καὶ τὸ τῆς τροφῆς ἐργαστικὸν καὶ δεκτικόν, οἷον στόμα καὶ κοιλίαν, πρὸς δὲ τούτοις, οἷς κινεῖται μορίοις ἕκαστον αὐτῶν)· εἰ δὲ τοσαῦτα εἴη μόνον, τούτων δ᾽ εἶεν [30] διαφοραί (λέγω δ᾽ οἷον στόματός τινα πλείω γένη καὶ κοιλίας καὶ τῶν αἰσθητηρίων, ἔτι δὲ καὶ τῶν κινητικῶν μορίων), ὁ τῆς συζεύξεως τῆς τούτων ἀριθμὸς ἐξ ἀνάγκης ποιήσει πλείω γένη ζῴων (οὐ γὰρ οἷόν τε ταὐτὸν ζῷον ἔχειν πλείους στόματος διαφοράς, ὁμοίως δὲ οὐδ᾽ ὤτων), ὥσθ᾽ ὅταν ληφθῶσι [35] τούτων πάντες οἱ ἐνδεχόμενοι συνδυασμοί, ποιήσουσιν εἴδη ζῴου, καὶ τοσαῦτ᾽ εἴδη τοῦ ζῴου ὅσαι περ αἱ συζεύξεις τῶν ἀναγκαίων μορίων εἰσίν τὸν αὐτὸν δὴ τρόπον καὶ τῶν εἰρημένων πολιτειῶν.

    Translation (William Ellis):
    […] thus, if we should endeavour to comprehend the different species of animals we should first of all note those parts which every animal must have, as a certain sensorium, and also what is necessary to acquire and retain food, as a mouth and a belly; besides certain parts to enable it to move from place to place. If, then, these are the only parts of an animal and there are differences between them; namely, in their various sorts of stomachs, bellies, and sensoriums: to which we must add their motive powers; the number of the combinations of all these must necessarily make up the different species of animals. For it is not possible that the same kind of animal should have any very great difference in its mouth or ears; so that when all these are collected, who happen to have these things similar in all, they make up a species of animals of which there are as many as there are of these general combinations of necessary parts.

This way of defining species seems to be the one involved in the History of Animals (I-1, e.g. 486b22 {{fr}}):

[…] ὁμοίως γὰρ ὥσπερ τὸ ὅλον ἔχει πρὸς τὸ ὅλον, καὶ τῶν μορίων ἔχει ἕκαστον πρὸς ἕκαστον.

Translation (Pierre Pellegrin):
According to the parts that each of the animals possesses, that is how they are simultaneously other and the same.

It’s by the comparison and the resemblance that Aristotle seems to define species, as in PA 639a18-19 where he exposes his method. So we can assume it is very near from modern definitions of species, e.g. like that of Cuvier:

The word species means those individuals who descend from one another or from common parents and those who resemble them as much as they resemble each other.

Recherches sur les ossements fossiles de quadrupèdes (Discours préliminaire), 1812

[…les individus qui descendent les uns des autres ou de parents communs et ceux qui leur ressemblent autant qu’ils se ressemblent entre eux.], translated by F. Zachos, in Species Concepts in Biology.


Some interesting references

I’ve used the first one for this answer.

  • Aristote zoologue, René Lefebvre
    A very interesting article, based on works by D. Balme and P. Pellegrin, however it’s in French.
  • Aristotle's Biology, Stanford Encyclopedia of Philosophy
    Not specifically about species definition, but interesting yet.
  • The Species Problem: A Philosophical Analysis, Richards A. Richards
    For a discussion of the many meanings of εἶδος in Aristotle’s works:

    1. As enmattered form (the appearance, the shape of the body, already in Homer);
    2. As principles of development and organization (this sense originated with Aristotle);
    3. A logical sense of εἶδος, as logical universals, from the Pythagoreans and Plato.

And, just after having finished to write this answer, this book:

  • Defining Species: A Sourcebook from Antiquity to Today, John S. Wilkins. Definitions can be found for other writers than Aristotle (the best is to read the book, partially available on Google Books, quotations aren’t very long):
    • Plato
    • Lucretius (De Rerum Natura, I, 159-158) (Epicurus’ teaching)
    • Pliny the Elder, whose Historia Naturalia was “the standard educated person’s encyclopedia of the natural world from its publication to the 18th century“ and is largely based on Aristotle: see vol. VIII, 44: “… quos percunctando quinquaginta ferme volumina illa praeclara de animalibus condidit. quae a me collecta in artum cum iis, quae ignoraverat, quaeso ut legentes boni consulant, in universis rerum naturae operibus medioque clarissimi regum omnium desiderio cura nostra breviter peregrinantes.” — translation (W.H.S. Jones): “To my compendium of these, with the addition of facts unknown to him, I request my readers to give a favorable reception, while making a brief excursion under our direction among the whole of the works of Nature, the central interest of the most glorious of all sovereigns.
    • Porphyry the Phoenician
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  • Thanks! Can you provide English translations or links to them for the Aristotle quotes? That would make this answer more accessible to many; currently the quotes lead to no conclusion for a reader who knows only English and Latin. My Greek is not fluent enough. I could read most of the French version, though. – Joonas Ilmavirta Nov 9 '16 at 7:41
  • This is great (+1), but I echo the above comment that we should try to offer translations of Greek. In addition, I think some point should be added that links Aristotle's view to that of Roman naturalists, since that is the point of the question. – brianpck Nov 9 '16 at 14:18
  • You're right, I add the translations now, and I'll see later for the Romans (I took literally or other ancients, for that matter :) ). – Luc Nov 9 '16 at 16:07
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    This is a very good answer. Perhaps I might underline (especially as this is not entirely clear from the pasted English translations) that, in their technical sense, genus is a calque on γένος and species on εἴδος. – fdb Nov 9 '16 at 21:34

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