Forthcoming in Theory in Biosciences
What is a species? Essences and generation
John S. Wilkins
Philosophy, University of Sydney
Tel.: +61 401 876 366
john@wilkins.id.au
http://evolvingthoughts.net/About
Abstract
Arguments against essentialism in biology rely strongly on a claim that modern biology
abandoned Aristotle's notion of a species as a class of necessary and sufficient properties.
However, neither his theory of essentialism, nor his logical definition of species and genus (eidos
and genos) play much of a role in biological research and taxonomy, including his own. The
objections to natural kinds thinking by early twentieth century biologists wrestling with the new
genetics overlooked the fact that species have typical developmental cycles and most have a large
shared genetic component. These are the "what-it-is-to-be" members of that species. An intrinsic
biological essentialism does not commit us to Aristotelian notions, nor even modern notions, of
essence. There is a long-standing definition of "species" and its precursor notions that goes back to
the Greeks, and which Darwin and pretty well all biologists since him share, that I call the
Generative Conception of Species. It relies on there being a shared generative power that makes
progeny resemble parents. The "what-it-is-to-be" a member of that species is that developmental
type, mistakes in development notwithstanding. Moreover, such "essences" have always been
understood to include deviations from the type. Finally, I shall examine some implications of the
collapse of the narrative about essences in biology.
Introduction
What is a species? Few questions have received so much attention as that over the
last century from biologists and philosophers of biology; perhaps only the
meaning of the term gene has been so contentious. We hear variously that a
species is this or that kind of entity, that they have this or that set of properties,
that they are classes or individuals, and that they are one kind of thing, or many.
Species are the “units” of classification, of evolution, levels of organization, mere
conveniences of thought, of operation and of communication. However, through
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all this there is what biologists and philosophers of biology say, and what
biologists do. No matter what theoretical considerations there may be that people
offer to justify their views, biologists still name species, describe them, conserve
them, and study them.
There is a widely held story that most people, if they have thought about the
matter at all, usually hold, which has been repeated for fifty years, since the
Centenary of the publication of the Origin. According to this view, sometimes
called the “essentialism story” (Levit and Meister 2006), and which many, like
myself, reject as historically inaccurate (Charles 2002, McOuat 2001, 2003,
manuscript, Winsor 2006a, b), before Darwin species were held to be universals,
classes or natural kinds, which had essential definitions. With Darwin comes
recognition of the variation within species, that drives evolution by natural
selection. From then on, biologists understood that species were polytypic, that
they had no essential properties. Species come to be understood to be biological
populations, protected against introgression by reproductive barriers, and
philosophically as individuals. In researching for my book, Species: a history of
the idea (Wilkins 2009), I came to realize that this was not accurate, and in fact,
for some definitions of “essentialism” that there never has been any such
essentialism in biology. Whether or not this is a reason for there not to be any now
is a matter for further discussion (e.g., Devitt 2008). Prior to the twentieth century,
the very idea of essence in biology almost always applied to a functional essence
rather than a taxonomic one1; what we might now call the physiology of a plant or
animal. Nehemiah Grew, for example, who introduced microscopy to botany,
1
As I am focusing on species rather than much higher taxa, it is an open question
whether there still was essentialism at the level of, say, kingdoms, but even here I
would say there is considerable vagueness, with, for example, so-called
“zoophytes” and the like; e.g., Bonnet (1745), cf. Pallas (1766), who is a critic of
the Great Chain approach, and the first to mention a tree metaphor for the division
between plants and animals. Even for him, though, zoophytes are a kind of
transition between kingdoms. Gradual transitions were the norm at all levels of
taxonomy.
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spoke of the essence of “the plant”, meaning that which made the stem, the leaf,
and the root and so forth, and not that which made a particular rose species (Grew
1682).
Discussion
The very word species has been a stumbling block in the essentialism story since
its inception. We know it as a term of art in botany and zoology, and more
recently across the entirety of biology, including viral species.2 But it originally
had no real technical meaning in natural history, despite being a technical term in
philosophy, theology, and psychology. It was, as John Locke noted, merely the
vernacular Latin word for “kind”. There was no implication that a species was a
class, or that there was an essential set of properties; species were just things that
naturalists began to pay attention to in the 16th century and thereafter.
The essentialism story developed gradually at first, in the comments about the role
played by Aristotle and scholasticism in natural history, in particular in Dewey’s
essay on Darwin and philosophy (below). However, where we might expect
essence of species to play a role in the criticism of prior thought, particularly
among the early Darwinians in the period from 1860 to 1900, we don’t. Instead
we find criticisms of the nature of investigation, or epistemological assumptions,
such as in the History of Botany by enthusiastic Darwinian Julius Sachs (1890),
the first edition of which was published shortly into the Darwinian period in 1875.
If we were to find this critique, we might expect it here of all places. Instead, we
find criticism of the Aristotelian program of doing science by definition, and of
teleology. The elimination of the latter was thought to be the major Darwinian
innovation.
As is often noted, the Darwinian revolution was as much an epistemological or
methodological shift as it was a theoretical one (Ghiselin 1974, 1997, Ruse 1989).
After the development of set theory, however, a distinction of the scholastics
2
It is also used for chemical, mineralogical, and other physical kinds. In addition
it has a special meaning in psychology, theology, philosophy and even in coinage.
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between intension, of sets that were circumscribed by definitions, and extension,
by member inclusion, was revived, and the logical tradition of species was held to
be a matter of intensional definition. In a seminal summary of the traditional preset theoretic logic of diairesis, or division, from the most general to the most
specific, H. W. Joseph (1916) made a clear distinction, as Whately had 90 years
earlier in 1826 (see below), between logical species and “natural” species, but the
developers of the essentialism story failed to pick this up, and read him as saying
that species of living things were the same as the logical species (as discussed in
Chung 2003, Winsor 2001, 2003, 2006a).
Around the time of the Centenary of the publication of the Origin, in 1959, this
story began to be developed, and it was elaborated over the subsequent period
until it became the received view in the history and philosophy of biology. In part
motivated by this story, and in part motivated by independent developments in
philosophy, a young philosopher of biology, David Hull, published a paper which
was titled “The effects of essentialism on taxonomy: two thousand years of stasis”
(Hull 1965), in which the claim was implicitly made that fixity of species was due
to Aristotelian influences. Actually, though, fixism was motivated by piety and
theology, not philosophy (as I document in my book), and essentialism in logic
was, if anything, a post hoc justification of that claim; or it would be if there were
strong historical evidence that essentialism in natural species was a widespread
view. Moreover, typology, as Winsor has argued, was ubiquitous as a “method of
exemplars” (Winsor 2003), and it remains the standard approach even today, by
Darwin and the evolutionists as much as by the idealists or fixists.
Dissent from the essentialism story began fairly early. Paul Farber’s work (1976)
indicates that “type” had a more complex and nuanced role in taxonomy in the
period immediately before Darwin than the essentialism story recounted.
Moreover, there is no reason to think that any of these senses had any essentialist
implications. Stung by criticisms of being “typological” by Mayr, some cladists
began to investigate the historical material, and argued similarly (Nelson and
Platnick 1981), and several others (Atran 1985, 1990, Stevens 1994) followed.
The original source of the confusion of the essentialism story appears to arise with
John Dewey’s widely read 1909 article “The influence of Darwin on philosophy”
(Dewey 1997), which begins “Few words in our language foreshorten intellectual
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history as much as does the word species.” This is true, and Dewey himself does
some of that critical foreshortening by not distinguishing the logical and
philosophical sense of species from the use it had amongst naturalists and
biologists, right from the beginning. He even writes
We dispose all too easily of the efforts of the schoolmen to
interpret nature and mind in terms of real essences, hidden
forms, and occult faculties, forgetful of the seriousness and
dignity of the ideas that lay behind. We dispose of them by
laughing at the famous gentleman who accounted for the fact
that opium put people to sleep on the ground it had a dormitive
faculty. But the doctrine, held in our own day, that knowledge of
the plant that yields the poppy consists in referring the
peculiarities of an individual to a type, to a universal form, a
doctrine so firmly established that any other method of knowing
was conceived to be unphilosophical and unscientific, is a
survival of precisely the same logic. This identity of conception
in the scholastic and anti-Darwinian theory may well suggest
greater sympathy for what has become unfamiliar as well as
greater humility regarding the further unfamiliarities that history
has in store.
So Dewey misled generations of thinkers by identifying what the scholastic
logicians, from whom we get the logical notions of genus and species, meant by
these terms with what naturalists meant, despite his plea for sympathy with them.
But logicians knew this was a matter of mere homonymy. The only thing in
common with logical and biological species was the word. Not even the logical
scheme into which Aristotelian logic placed genera and species was copied in
natural history3 – unlike with logical kinds, there was only one level of genus and
species in biological taxonomy, and many logic writers of the nineteenth century
expressly stated that the meanings were different: One example in 1826, which is,
note, when Darwin was still at university, is given by Archbishop Richard
Whately, whose Elements of Logic (Whately 1875, original edition 1826 in the
Encyclopedaedia Metropolitana) revitalized the study of logic by philosophers
and mathematicians in the English speaking world:
3
Some early thinkers, such as John Ray (1696) do explicitly appeal to the genus-
including-species schema of logic, but they then proceed to employ it quite
differently in their taxonomic work.
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... if anyone utters such a proposition as ... “Argus was a
mastiff,” to what head of Predicables would such a Predicate be
referred? Surely our logical principles would lead us to answer,
that it is the Species; since it could hardly be called an Accident,
and is manifestly no other Predicable. And yet every Naturalist
would at once pronounce that Mastiff, is no distinct Species, but
is only a variety of the Species Dog. ...
... the solution of the difficulty is to be found in the peculiar
technical sense ... of the word “Species” when applied to
organized Beings [a term that preceded the use of “organism”]:
in which case it is always applied (when we are speaking
strictly, as naturalists) to individuals as are supposed to be
descended from a common stock, or which might have so
descended; viz. which resemble one another (to use M. Cuvier’s
expression) as much as those of the same stock do. [Elements of
Logic (1826) Bk IV, ch. 5 §1 p183; 1875 fifth edition used]
On the older logic of division, the essence of a thing was known by dividing
general classes (genera) into specific sub-classes (species, hence the names), and
the division gave you the differentiating characters that made them what they
were – the essences. But Whately knew this was not the case in biology:
[The fact of two organisms being the same species] being one
which can seldom be directly known, the consequence is, that
the marks by which any Species of Animal or Plant is known,
are not the very Differentia which constitutes that Species. [Op.
cit., p184f]
It’s no accident that Whately quotes Cuvier; all educated readers of the day knew
Cuvier’s definition, which is itself a reworking of the definition given by John
Ray in 1686, when the term species was given its first biological technical
meaning. Ray wrote:
In order that an inventory of plants may be begun and a
classification of them correctly established, we must try to
discover criteria of some sort for distinguishing what are called
“species”. After long and considerable investigation, no surer
criterion for determining species has occurred to me than the
distinguishing features that perpetuate themselves in propagation
from seed. Thus, no matter what variations occur in the
individuals or the species, if they spring from the seed of one
and the same plant, they are accidental variations and not such
as to distinguish a species … Animals likewise that differ
specifically preserve their distinct species permanently; one
species never springs from the seed of another nor vice versa.
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(cited in Cain 1999, from Ray 1686 tome I, Libr. I, ch. XX, page
40)
Notice what Ray does here – although there is a mention of accidental variation,
he does not appeal to the essence of a species, but to generation: the
“distinguishing features that perpetuate themselves in propagation from seed”.
This is a causal definition of species; and the features must make more of
themselves.4 It is not an arid Aristotelian definitional version, and nor is Cuvier’s:
… the word species means the individuals who descend from
one another or from common parents and those who resemble
them as much as they resemble each other. Thus, we call
varieties of a species only those races more or less different
which can arise from it by reproduction. (Cuvier 1825; emphasis
original, 1831)
There must be resemblance, but there has to be generation, and versions of this go
as far back as the Epicureans, which I call the Generative Conception of Species.
So logicians at one time knew this homonymy; by the time the essentialist story is
in full flight, it has been forgotten. It is not coincidental that it was first forgotten
at the time when genetics was being developed and elaborated.
Prior to around 1904, there was no such thing as the “species problem”. Instead,
there was a wholly different problem; the “species question”, the “mystery of
mysteries” that Darwin quoted from Herschel on the first page of the Origin of
Species.5 This was the question of the origin of species, which is why Darwin
gave his book the name that he did. Darwin thought that he resolved that question,
contrary to what textbook writers often say about him. That is discussed in my
book, however; for now, note that the species problem arises at the time we think
we have solved Grew’s question of the functional essence of organisms – their
genes. A number of geneticists, such as Thomas Hunt Morgan, had denied that
4
Phillip Sloan (2009) calls this speciesH for the historical and material sense of
species (cf. Kung 1977).
5
I am greatly indebted to Jody Hey for asking me when the use of “species
problem” began, leading me to notice this shift.
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species exist, and held that only genes do. The myth that Darwin also thought
species were mere conveniences arose about then. Other geneticists, such as de
Vries, proposed that an “elementary” species was properly to be thought of as a
“pure line” of genes, and Lotsy defined a “Jordanon” as a group of genetically
identical individuals, and a “Linneon” as the Ray-style definition of those who
resemble each other more than any other group, but without the generative aspect.
In 1908, a symposium published in American Naturalist (Arthur 1908, Bessey
1908, Boyd 1908, Britton 1908, Johnson 1908, Lewis 1908, Macdougal 1908)
concluded that species were not real, and so the “species question” gave way to
the “species problem”, although the qualifier itself had been used by William
Bateson before the Mendelian revolution began (Bateson 1894, 2).
Essences according to the new geneticists were, in other words, genetic, and if no
groups of organisms shared identical genetic constitutions, then there were no
species. The new science was also concerned to establish itself against museum
taxonomy, and so comments critical of “morphological” diagnosis of species
began to appear in the literature. Dewey’s identification of the concerns of the
scholastics with those of pre-Mendelian biologists merely reinforced the growing
tendency to deprecate those who had gone before.
However, biologists weren’t stupid or blind before Darwin, nor did they become
clever and good observers simply by working after him and Mendel. They knew
of species before they had a theory to go by that accounted for them, or a system
of systematics to classify them with. They knew that species were variable, that
they were usually but not always interfertile only with conspecifics, that they had
typical forms and habitats, and generally that they were caused by a generative
power or propensity, even if they had poorly formed notions of what caused that,
or how it worked. This is even true of the pre-scientific herbalists who often
reliably identified modern botanical species (Stannard 1979, Stannard et al. 1999).
This raises some interesting questions about the philosophical nature of species. Is
it a question of theory whether species are real? Do we need to have a theory like
genetics before we can ask what they are? Does the notion of species rely upon
some more primitive concept, like population or gene pool? I believe the answer
to all three questions is, No.
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Species were not invented to be units of classification6, nor were they ever defined
on a philosophical and logical basis. Such essences as they did have were always
generative, rather than definitional, and the term most often used for the nature of
species is “type”, not “essence”, which latter term is used almost exclusively to
denote the key identifying traits to be used in the field, garden or market place
(the “Essential Characters” of the botanies of the post-Linnaean era). Essential
characters are merely diagnostic aids, and no more are thought by pre-Darwinians
or post-Darwinians to be the causes of particular species than a cross-vein on a
wing used to identify a Tetriphid fruit fly is the cause of it being the sort of animal
it is.7 If species are indeed thought to have essences, they are of the developmental
kind – a lifecycle that reliably generates the morphology, ecological niche
occupancy and behavior that is typical. Because the species problem was posed in
the context of genetics, and in particular in terms of shared genes, a promise that
was quickly dashed by the discovery of polytypy and pleiotropy in natural
populations of animals (Robson 1928), at least, it became a kind of problem with
essentialism, or rather it set up the conceptual preconditions for creating the
essentialism story later, when the Modern Synthesis, so-called, had effectively
won the day.
There is also a parallel series of stories also to do with essentialism in philosophy,
via Karl Popper’s attack on what he called methodological essentialism (Popper
1959), which may or may not have actually existed amongst scientists and social
scientists, and in metaphysics to do with nominalism and the nature of individuals
(Strawson 1964), at about the time the essentialism story was invented. Various
authors have traced these diverse influences on the essentialism story, but the
general message is clear: it is a back-rendering, what gamers and comics
6
I am therefore disagreeing with John Dupré (2001) that they were first units of
classification. However, he is correct that they were not units of any theory of
biology when they were introduced.
7
Even Linnaeus distinguished between characters and notae; effectively between
diagnostic marks and real properties.
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aficionados call “ret-conning” (making stories retroactively consistent), of the
history to make the issues of the present time, around the 100th anniversary of
Darwin’s birth when it began, seem to be eternal ones in the history of biology,
and indeed to show history to be progressive, something scientists more than most
seem to need to believe of their own disciplines. While it is good rhetoric and
understandable, it is bad history, and it even has a special name in historiography
– the sin of Whiggism (Butterfield 1931).
Still, if the essence of a species is not simple, and there are alleles, clines,
inversions and all the other variation in the constitution of members of species,
then that is not the essence of a Popper or an Aristotle in any event. So does
essentialism need to be harmful? The answer to that is, I think, to be found in a
third parallel story, about the nature of natural kinds in philosophy. I will briefly
rehearse it here.8
At the turn of the 19th century, taxonomists knew very well that taxonomic
classes were variable, but that they usually had a typical form. This was, you will
recall, before the invention of statistics; today we might say that most taxa have a
modal form. In a discussion of what counted as a kind in natural history, William
Whewell in his Philosophy of the Inductive Sciences (1840) gave a good account
of natural kinds as being types from which there were deviations, although he
treated species themselves as simple objects. John Stuart Mill disagreed and
asserted that natural kinds were definable and had universal (causal) properties for
all members (Mill 2006).9 For Whewell, the type of the taxonomist was a natural
kind; for Mill, it was the element and the compound of chemistry and physics.
Still, I believe the weight of venerable history is on Whewell’s side, not Mill’s, or
to put it another way, that Mill’s conception of natural kinds is not something that
applies well to historical sciences that are restricted to specific domains, like
natural history or taxonomy. And despite what we might think based on the
8
It is the topic of a forthcoming paper of mine on natural kinds in biology.
9
The difference between Mill and the Aristotelian project of science by definition
is that Mill expected these properties to be causally active or constitutive.
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discussion of logic from Frege onwards, as late as the early 20th century, for
instance with John Venn (1866) and others, a natural kind was indeed typically
thought to be a kind of living beings, caused by generation (Hacking 1991).
So much of the confusion about essences can be resolved if we do not adopt the
view that Mill introduced, that a real Kind must have a set of necessary and
sufficient properties. For Mill, a species would be a natural kind (a phrase
introduced by Venn, although he did not adopt the Millian view regarding it; Mill
just used the word Kind) if it had some set of universally shared properties that
made each organism a member of it, rather like having a certain number of
electrons, positrons and neutrons makes each atom of an element that element. By
contrast, for Whewell, and for those taxonomists who he was accurately
describing in the Philosophy of the Inductive Sciences, to be a member of some
group, a species, a genus, and so on, is to be mostly like the typical form, and to
be something that can be supposed to share a genealogy with that form. This sense
of “essence” is something that, I believe, is quite consistent with our present
understanding of genetics and populations; most members of most species share
most genes, but there are multiple genetic controls over some typical traits, and
some species have major genomic varieties. David Hull has said that there is
nothing so unusual or absurd in biology that some species doesn’t have it
somewhere or somewhen; I call this Hull’s Rule. To be an essentialist in the world
of Hull’s Rule means that you cannot insist that taxa are going to always have
some set of genetic or other causes, but it doesn’t mean that you can’t say that
taxa mostly share causes. To be a taxon, I think, is to have some set of general
properties, the bulk of which any member will share.10 This is sometimes called in
philosophy the “family resemblance predicate”, after Ludwig Wittgenstein’s
example in the Philosophical Investigations (Pigliucci 2003, Wittgenstein 1968),
but over a century before Wittgenstein, Whewell made just this case. Families
resemble each other because they share generative histories and hence generative
causes, but they share them typically.
10
And to not share them would mean that no taxon could be identified in any
case. If there is a taxon, there must be some shared general properties.
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The thesis known as the Individuality Thesis (Gayon 1996, Ghiselin 1997, Hull
1978), in which species are considered to be not kinds, but named objects that
have a historical location, is a defense of biology, and especially genetics, against
the encroachment of Mill’s notion of a Natural Kind. Sure, say the individualists,
species and other biological taxa are not Natural Kinds (as defined by Mill). The
only other metaphysical notion open to philosophers of taxonomy is that of an
Individual, a thing that exists in one time and one place or region, and has a start
and an ending. Hence, species are Individuals. I cannot fault this logic – species
clearly aren’t the kinds of Kinds that Mill required, and they actually are
historical objects, so I have no objection to their being called Individuals; but I do
think they have “essences”, or, rather, typical developmental systems and
responses to typical environments; to preclude confusion, let us call these
developmental types.
There is a recondite argument in metaphysics as to whether individuals in the
metaphysical sense can have an essence – some say not, others say they can. I
won’t rehearse it here, as it is of interest only to a certain kind of philosopher.
However, there’s a much older sense, Aristotle’s, that I think works well for
individuals. Aristotle did not have a technical term for essence, especially not for
natural objects, but instead he used the phrase “the-what-it-is-to-be”11. We can
usefully ask what it is to be a member of a species. Generally, it is to share a
genetic, developmental and ecological process. To be a member of Homo sapiens
is to have some majority of typical properties: a certain number of chromosomes,
genes, cell types, and ecological resources that reliably result, most of the time, in
the morphology of the typical members of the species (Pigliucci 2003, Pigliucci
and Kaplan 2006). We can investigate this and list these properties (although we
must be careful not to call the first genome, such as Craig Ventner’s, the “typical”
genome); this is a matter of empirical research. It is not a matter of definitions, it
is a matter of finding out what the developmental types are by sampling
populations and periods.
11
τό τὶ ἦν εἶναι, e.g., Top. A.5, 101b39, E.3, 153a15–16, Met Δ.6, 1016a33
(Baum 2009). The term “essentia” was a Latin backformation.
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No philosopher of language who is inclined to the Millian kind of Kinds or to
linguistic or logical essentialism is going to be happy with this, just as family
resemblance predicates haven’t been greatly liked by such philosophers in general
(but see Gasking 1960), but it is a sense of the essence of species that is at once
compatible with the biology, and consonant with the original history of the notion
of essences. Species can be metaphysical Individuals, and yet have something
mostly shared between its members, which can be granted the honorific of
“essence”, the what-it-is-to-be a member of that species, its developmental type.
Still, this doesn’t solve the question of how we identify the Kind in the first place
– we have to know there is a Kind before we start to investigate the essence of it
in any sense. Consider a parallel case in physics: the periodic table of Mendele’ev
(Hettema and Kuipers 1988, Scerri 2007). By gathering together the observed
properties of chemical elements, refined over time, a table was created without
theory that was later explained by valency theory, and ultimately by quantum
mechanics. There was an assumption that there were Kinds, but they were
observed rather than defined. Taxa are phenomena that call for a theoretical
explanation, rather than the units of some prior taxonomy or the variable of some
prior theory. Again, this is not unlike Aristotle’s own theory and practice (Charles
2002, p4).
With respect to recent attempts to “reintroduce” essentialism into taxonomy, as
opposed to functional biology, it appears to me that the objections against it that
were raised in the 1960s and thereafter remain valid. No set of shared properties
are common to every member of a taxon, nor to only members of that taxon, for
all taxa; and in that respect the modern philosophical notion of essence (of Kripke
1980, and I think Devitt’s also) is biologically unnecessary. But a less malignant
sense, in which all members of a taxon must share most of some set of “essential”
properties to make them what-it-is-to-be members of that taxon, is perfectly
coherent and biologically respectable, and it is that role that Aristotle actually
seemed to think essences played, which I am calling developmental types. In my
book I argue that Aristotle was not a taxonomic essentialist; he was, perhaps, a
physiological essentialist and maybe that is the same thing, though I doubt it (see
Charles 2002). Nevertheless, he and everyone else assumes that to be a member of
some kind in biology, organisms must share the bulk of their properties by
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inheritance. This is the elaborated version of the tradition generative conception of
species for the modern day, and it is either done in terms of genetic clustering
(Cohan 2002, Mallet 1995, Rosselló-Mora and Amann 2001), or of demographic
and ecological interchangeability (Templeton 1989, Templeton 1998) or of
genealogical coalescence (Baum 1998, 2009).12
Conclusions
I consider therefore, that essentialism is a straw-man target in biology, and that
both taxonomic and developmental types are acceptable to use; indeed they are
inevitable. Moreover, classification in biology is largely inductive, and not
generated by theory, although there is no reason why a theory cannot suggest
further ways to inductively classify. The requirement that classification be
“theory-free” represents a now-defunct philosophy of science. It suffices that one
does not use theory to support a classification that in turn is used to support the
theory in a vicious circle.
Natural kinds that apply to biology (and the other historical sciences) are specified
by types, not definitions or essential properties. The Millian notion of a Kind as a
set of necessary and sufficient causal properties is something that fails abysmally
in what Whewell called the palaetiological sciences, and which are now referred
to as the “special” sciences. It works fine for the “general” sciences (again, the old
genus–species distinction in play) where instances of a kind are the same
everywhere, but in the special sciences, things are at best only approximately
interchangeable and identical, and so the kinds are formed not by exact
resemblance but by identity under every modification of form and function, as
Owen defined homologies.
Furthermore, we must not think that biologists needed Darwin to see the world.
Human beings are good or bad observers in direct proportion to the care and
12
The philosophical account that best represents this is Richard Boyd’s notion of
a homeostatic property cluster, or HPC, kind (Boyd 1999). It works, I think, for
the most basal kind, but I do not think it applies to supraspecific kinds.
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Forthcoming in Theory in Biosciences
concern they take for their subjects. Where biological differences matter, as in
herbal remedies, they identify species well without the need for science, but of
course as the science becomes more elaborate and detailed in its findings, it
refines likewise the folk taxonomies of ordinary culture (Atran 1990, 1995, 1998,
1999). Nor was Darwin irrelevant; his work changed the perspective from which
we address taxonomy; it may even go so far as to undercut the “intuitive” ranks
that Atran identifies in folk taxonomy (Godfrey-Smith 2009).
So it’s OK to talk about essences, types (and typology!) and specific natures; so
long as they aren’t Mill’s kinds of Kinds (unless they, in fact, are).
Acknowledgements
This work was done under the ARC Federation Fellowship FF0457917 of Prof.
Paul Griffiths, and under ARC Postdoctoral Fellowship Grant DP0984826, at the
Universities of Queensland and Sydney, respectively. Many thanks to Ciências
Viva, and the Faculdade de Ciências of the Universidade de Lisboa for inviting
me to Lisbon to deliver the talk this paper is based upon and funding that visit,
and to Dr Nathalie Gontier for hosting an Australian above and beyond the call of
duty.
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