Scientific Classification

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Scientific Classification
John Dupré
ESRC Centre for Genomics in Society
University of Exeter
It is often supposed that one of the goods delivered by successful science is the
right way of classifying the things in the world. Surely there is something right about
this: any body of scientific knowledge will include ways of classifying, and will not serve
its intended aims unless the classifications it embodies reflect real differences and
similarities in the world. The standard paradigm for such a successful scientific
classification is the periodic table of the elements.
But there is also much potentially wrong with the supposition just mentioned.
Most importantly, there is a highly questionable implication of there being some uniquely
best classification. Classifications are good or bad for particular purposes, and different
purposes will motivate different classifications. It may be that there is such an ideal
classification for chemistry, but if so it is because of the specific aims implicit in the
history of that discipline. Chemistry aims at the structural analysis of matter and if, as
appears to be the case, all matter is composed of a small number of structural elements, a
classification based on those elements will be best suited to these purposes. It is also
often the case that chemical structure will be the best guide to the properties of kinds of
matter. But not necessarily. Two quite distinct chemicals are referred to as ‘jade’ and

despite some serious debates on the issue, Chinese jade carvers have decided that both
are real jade (LaPorte ).
This illustrates the general point, which becomes much more obvious when we
move from chemistry to biology, that classifications devised for different goals can be
cross-cutting and overlapping (Dupré, 1993, part1). There remains among many
biologists and philosophers the hope of finding the ultimate and uniquely best
classification of organisms, most recently conceived in terms of the speciation processes
of Darwinian evolution (e.g., De Queiroz, 1999). However, it is at the same time
becoming clearer that there is very likely no such ideal classification. There is no reason
why a classification that reflects the origins of the things classified should coincide
exactly with one aimed at the ecological relations of those things, and it is increasingly
perceived that these can and do diverge (Dupré, 2002, chs. 3-4). This possibility
becomes even clearer in view of the difficulties that are emerging in the project of
evolutionary-based classification. Speciation was once seen as an all or nothing affair
leading to complete isolation of one group form another. It is now clear that for micro-
organisms, in particular, there is very little such isolation, and genetic material moves in
many ways from one kind of organism to another. In fact it has become common to
conceive of the genome of an ecosystem (the soil of an area, or a body of water) rather
than the privatised genome of an individual organism (see e.g. Venter et al., 2004). The
classical picture of speciation applies quite well to some of the most complex multi-
celled organisms, such as mammals and birds, though much less well to plants. An
important movement in biology is to transcend the anthropocentrism that takes the
peculiarities of our own corner of the living world as the model for all.

The recognition that even within science there is no objectively given
classificatory order allows the realisation that there is nothing inherently inferior about
the biological classifications developed by non-scientific folk for non-scientific purposes.
This point has been obscured for philosophers by the highly influential proposal by
Hilary Putnam (1975) that ordinary language terms for naturally occurring kinds of thing
or stuff were primitive attempts to refer to the kinds that science would eventually
delineate more accurately. My own view is that science is generally quite unable to do
this, and that ordinary language terms are generally just fine as they are for the purposes
fore which they have been developed (Dupré, 2002, chs. 1-2).
A graphic illustration of what I have in mind here can be gained from reflection
on the wisdom taught to all young children that science has discovered that whales are
not fish. No doubt this wisdom long antedates Putnam’s proposal, and shows that such
intuitions about the achievements of science are widespread. Nonetheless it is very
difficult to provide a convincing rationale for the ‘discovery’ that whales are not fish.
‘Whale’ in ordinary language refers to all the members of one branch of the family
Cetacea (the Baleen whales) and the larger members of the other branch (the toothed
whales). The smaller members of the latter group, dolphins and porpoises, are not
generally referred to as whales. Large cetacean is not a concept that has any great
biological significance. ‘Fish’ is much worse. Even assuming it doesn’t encompass
shellfish or jellyfish, there are three groups of aquatic vertebrates generally thought of as
fish, but groups that have diverged for hundreds of millions of years. In fact a lungfish,
being part of the aquatic lineage from which terrestrial vertebrates evolved, is more
closely related by descent to a whale (or, for that matter, a human) than it is to a salmon

or tuna. In short, since these are not significant scientific terms it is impossible to see
how science can have discovered facts about their reference.
A final problem with scientific classification raised by the formulation with which
this note began, is that ‘things’ are often distinguishable only after classification, rather
than presenting themselves to be classified in full-fledged thinginess. So for example it is
obvious to common sense that a tree is an individual thing. But from one biological
perspective a copse of elm trees, all suckers from the same root system, should be seen as
a single individual. A more interesting example is the recent development of the concept
of a gene. The more science finds out about the workings of DNA inside living cells, the
harder it is to find principled ways of dividing the DNA into components suitable for
classification into anything related to the historical meaning of ‘gene’ (Moss, 2001, Stotz
Griffiths, and Knight, 2004; Dupré 2004). Of course this is not normally a problem for
molecular biologists in the context of their professional lives, but it can lead to serious
misunderstanding of many things they say.
References
De Queiroz, K. (1999), “The General Lineage Concept of Species and the Defining
Property of the Species Category”, in R. A. Wilson (ed.), Species: New Interdisciplinary
Essays, (Cambridge, Mass.: MIT Press/ Bradford Books).
Dupré, J. (1993), The Disorder of Things: Metaphysical Foundations of the Disunity of
Science, (Cambridge, Mass.: Harvard University Press).
Dupré, J. (2002), Humans and Other Animals, (Oxford: Oxford University Press).

Dupré, J. “Understanding Contemporary Genomics,” Perspectives on Science, 12, 2004,
pp. 320-338.
LaPorte, J. (2004), Natural Kinds and Conceptual Change, (Cambridge: Cambridge
University Press).
Moss, L. (2003), What Genes Can’t Do, (Cambridge, Mass.: MIT Press/ Bradford
Books).
Putnam, H. (1975), “The Meaning of ‘Meaning’”, in Mind, Language and Reality,
Philosophical Papers, ii, (Cambridge: Cambridge University Press).
Stotz, Karola, Paul E Griffiths, and Rob D Knight. 2004. “How scientists conceptualise
genes: An empirical study”, to appear in Studies in History & Philosophy of Biological
and Biomedical Sciences. (http://www.pitt.edu/~kstotz/genes/draft%20paper.pdf).
Venter, J. C. et al. (2004), “Environmental Genome Shotgun Sequencing of the Sargasso
Sea”, Science, Apr 2, 2004; 304(5667), pp. 58-60.
John Dupré is Professor of Philosophy of Science at the University of Exeter, and
Director of the ESRC Centre for Genomics on Society. He has formerly held positions at
Stanford University and Birkbeck College, London. His main area of research is in the
philosophy of biology. His publications include The Disorder of Things: Metaphysical
Foundations of the Disunity of Science (Harvard, 1993); Human Nature and the Limits of
Science (Oxford, 2001); Humans and Other Animals (Oxford, 2002); and Darwin’s
Legacy: What Evolution Means Today (Oxford, 2003). He is currently collaborating with
his colleague Professor Barry Barnes on a book that will provide an introduction to
contemporary genomics from a sociological and philosophical perspective