Before developing his theory of variation and natural selection, Darwin confronted a crippling grammatical problem in the work of the naturalists of his day. Individual races of animals were designated as both ‘species’ and ‘variation’ by contemporary naturalists, sometimes even by a single researcher at different points of his career. The distinction between ‘species’ and ‘variation’ may seem mundane, but in fact the difference is of principle importance. It is precisely this distinction that lead to Darwin’s inquiry into the origin of species and the consequent revolution of biological research. The equivocation of these two terms – species and variation – in a single breed, the carrier pigeon for example, attributes to that breed both a unique and a shared origin. The conflation at once affirms and denies the relation of a single breed to other, similar looking breeds. The conflation, besides being a perfect contradiction, exposes the difficulty of subsuming the careful observations of an experimental scientist under Aristotle’s categorical logic. Darwin’s study of domestic and natural variation and selection required – and requires – a review of the logical act of predication.
When we look at any thing and ask “Why?” we are searching for a cause. Where did it come from? How was it made? What (or who) made it? What’s it for? These are, at least, the questions Aristotle tells us are implied by the question “Why?” The final cause, implied by the question, “What for?” designates the purpose of a thing. This purpose – ‘telos’ in greek – designates the stage of a process or movement at which point an individual thing has achieved the pinnacle of its existence. For a man it is when he has begun to exhibit the rational activity characteristic of human beings; for a tree, when it is capable of reproduction. Every thing has such a purpose, and those things that share the same purpose are of the same kind. Whenever we attribute a definition to a thing, then, we associate it with the things that share the same ‘telos’.
We can do this, that is, define, any individual. Socrates, we can say, is both a man and an animal. He is best defined, however, by the former, because the term ‘man’ associates Socrates with the class that shares the ‘telos’ most peculiar to him. Aristotle explains this in the first five chapters of his Categories, when he establishes all that pertains to Substance, which is the first of his eight non-composite descriptors.
“… if any one should render an account of what a primary substance is,” says Aristotle, “he would render a more instructive account, and one more proper to the subject, by stating the species than by stating the genus… for the former description is peculiar to the individual in a greater degree, while the latter is too general.” (2b10)
What is species? Aristotle calls it a ‘secondary substance’, i.e. the first predicate of primary substance. Perhaps the more urgent question is, then, “What is substance?” Aristotle defines it thus: “Substance, in the truest and primary and most definite sense of the word, is that which is neither predicable of a subject nor present in a subject; for instance, the individual man or horse.” (2a15)
Let’s parse this. To be “present in a subject” Aristotle says, is to be “incapable of existence apart from the said subject.” (1a20) About “predicable of” he says: “Of things themselves some are predicable of a subject… Thus ‘man’ is predicable of the individual man…” Also, “…that which is individual and has the character of a unit is never predicable of a subject.” (1b5)
Putting this all together we get a definition of substance: Substance is an expression used to speak of an individual and which is not dependent on any particular individual for its existence as a class. We can describe species, a secondary substance, as an expression which subsumes an individual under a class whose definition exists apart from but is peculiar to that particular individual. “… of secondary substances, not only the name, but also the definition, applies to the subject.” Thus ‘man’, which is Socrates’ species, “… is predicated of the individual man, but is not present in [him]; for manhood [the definition of man] is not present in the individual man.” (3a10)
Note, in particular, that the definition of any particular species is not present in any individual of that species. Whatever it is that distinguishes a particular man as a member of that species, then, is not to be found in that man. Otherwise, this distinguishing feature is not part of man’s definition. In calling Socrates a man we are not speaking of any particular quality that distinguishes him as such; rather, we are making an inference. Several things, some of which we are perhaps not explicitly aware of, lead us to say that Socrates is like his friend Alcibiades, and for the same reasons, we say that Socrates and Alcibiades are like Meno. This conglomerate of qualities that we find in each individual we thus call ‘manhood’, and since we cannot give a full account of it, we say it is not in any one of these men, though we affirm it of them all nonetheless.
The predicate ‘species’, then, is both a grammatical and a metaphysical construction. It is grammatical insofar as it is part of a grammatical proposition. We either affirm or deny that ‘man’ is an appropriate defining term for Socrates. It is metaphysical insofar as we are thus affirming or denying a classification of Socrates’ being. What is Socrates? Socrates is a man. When we predicate him this way, we must also ask, “What is man?” and in doing so we ask for a definition of ‘manhood’ – that unique conglomeration of qualities that exists apart from any individual. In accordance with Aristotle’s definition in the Nicomachean Ethics, we can say that ‘manhood’ is an “activity of soul in accordance with virtue,” (1098a15) a definition which is also the expression of man’s ‘telos’. To be man is to partake in this activity, and this is how we predicate each individual Socrates, Alcibiades, or Meno.
For Darwin, the fact that Aristotle’s definition of ‘species’ admits of contrary qualities was especially confounding. Again in the Categories, Aristotle says:
“The most distinctive mark of substance appears to be that, while remaining numerically one and the same, it is capable of admitting contrary qualities… one and the self-same substance, while retaining its identity, is yet capable of admitting contrary qualities.” (4a10-15)
While the above may be interpreted mundanely to say that Socrates is a man whether sleeping or awake, since the limits of the admissible variety is indefinite, the interpretation may be taken much further. “What,” we can ask, “is the degree of change that will violate the above definition of man, and thus change his species?”
This is precisely the question asked by Darwin in his On The Origin of Species. In Chapter II, ‘Variation Under Nature’, he poses the question:
“A wide distance between the homes of two doubtful forms leads many naturalists to rank both as distinct species; but what distance… will suffice? if that between America and Europe is ample, will that between the Continent and the Azores, or Madeira, or the Canaries, or Ireland, be sufficient?” (Origin, p. 49)
Here and in surrounding passages Darwin shows that it is specifically this unique quality of substance – the capacity to admit of contrary qualities while retaining a single identity – that renders the term species troublesome and nearly meaningless in a classification of the natural world. The definition of species gleaned from Aristotle – that it is a class predicable of but not dependent on individuals for its existence – is not, by itself, rigorous enough to delineate the natural world in a meaningful way. As it stands it admits of too much variation and does not provide a method for inferring the species of any individual.
Darwin found that livestock breeders, men who should be most intimate with the fact of shared origins between races of animals, were nonetheless staunch in believing that each of their breeds descended from distinct ancestors. Perhaps it is understandable for naturalists to make this inference, provided that they did not look at racial changes over time, but how could breeders sustain such a belief regarding their own animals? Darwin heeds the oversight of these breeders, and describes their folly: “… they ignore all general arguments, and refuse to sum up in their minds slight differences accumulated during many successive generations.” (Origin, p.51) Thus he pays particular attention to the differences “of small interests to the systematist” in order to recognize distinctions previously unseen. The differences he noticed would allow Darwin to mark the stages of change between contemporary species, and thus to trace the common origin of seemingly unique species.
If we are to predicate an organism with the name of a species, we should also be able to definitively affirm or deny this predicate. Darwin, with his theory of variation, natural selection, and origin of species, allows us to make such definitive predications. His recognition of the shared origins of seemingly distinct species required a re-articulation of what it means to predicate an individual with the term species, and now, though we must be more careful, we may be more certain in our application of it. To retain species “as a special act of creation,” (p.55) he says, would be to contradict observations of natural variation, such as the fact that “wherever many species of a genus have been formed, the species of that genus present a number of varieties, that is of incipient species, beyond the average.” (p.56)
We must, then, view the definition of substance, and species in particular, from a new perspective. We may still understand it as an expression whose existence is independent of that of any individual predicated by it, but we can no longer view this existence as substantial or essential. Neither, then, can its role as predicate be substantial or essential. Darwin says it best in his conclusion to On The Origin of Species:
“In short, we will have to treat species in the same manner as those naturalists treat genera, who admit that genera are merely artificial combinations made for convenience. This may not be a cheering prospect; but we shall at least be freed from the vain search for the undiscovered and undiscoverable essence of the term species.” (p.485)
Aristotle’s Categories still stand as grammatical devices, and we may still predicate using the term species. What we can no longer do, however, is demand more from the term than its nominal convenience.