What's in a name? A history of
taxonomy
Taxonomy is arguably the world's oldest profession, and naming and
classifying what's around us is part of the human condition. Scientific naming
began with the Swedish botanist Carl Linnaeus in the eighteenth century. Scientists
still use his system, but how much has the science changed from the days when
Linnaeus, in a frock coat and with a powdered wig, classified the Earth's
plants and animals?
The ancient Greeks and Romans named and classified organisms,
particularly those that were useful to them. They had names for medicinal
plants and for the animals they hunted and those that they feared. This
tradition was carried on in northern
This is an example of one of the primary problems of the names of
organisms. Names get changed with use--Poma amoris, the love apple, started
life either as poma di Mori, the apple of the Moors or poma di ori, the golden
apple. Over time, the vernacular name became corrupted to poma amoris, and the
tomato was presumed to be a powerful aphrodisiac.
At about the same time, in the late sixteenth century, the science of
scientific naming started. Plants and animals were given long, polynomial Latin
names. At that time Latin was the language of scholarship--a logical choice for
scholarly naming. For example, the humble tomato was given the long Latin
polynomial Solanum caule inermi herbaceo, foliis pinnatis incisis which means
the 'solanum with the smooth stem which is herbaceous and has incised pinnate
leaves.'
In the eighteenth century, people working with plants and animals
started trying to name things formally, and to use those names consistently. This
became increasingly problematic as diversity increased. Initially, only local
organisms were known but as other lands, such as the
Linnaeus and a new way of naming
In the mid-1700s a young Swedish doctor, Carolus Linnaeus, went on a
journey to
Linnaeus was a medical doctor, as were all botanists at that time. Until
recently, all medicine had been based on herbalism and doctors had to study
botany in order to learn their craft. So botanical taxonomy
originated with the need of doctors to identify plants correctly. Linnaeus
kept plant specimens in his own herbarium. He was fascinated by plants from all
over the world and would often travel to examine other people's collections.
Linnaeus was interested not only in plants but in all living organisms. He
collected a huge variety of plants and animals and started looking for a system
in nature. He was trying to describe all the things that had been put on Earth
by the Creator, and therefore approached taxonomy with the tacit assumption
that this task was finite.
In the course of his work, Linnaeus did two critically important things
for the development of taxonomy. The first was to invent what is known as the
sexual system. Instead of looking at the totality of a plant, as would a herbalist, he concentrated on one particular character--and
organised all plants according to that character. The characters that he chose
were the number of stamens, the male parts, and the number of pistils, the
female parts. This was controversial at the time to the extent that he was accused
of being a botanical pornographer! His rivals criticised his system as
'loathsome harlotry (scortationes quasi destabiles)'. It was thought that
ladies shouldn't deliberately look at the sexual parts of plants. But despite
this disapproval the sexual system soon caught on because it was so accessible
and straightforward. It represented a democratisation of science in that
anyone, not just a specialist, could look at a flower and count the number of
male parts and female parts.
In this way Linnaeus made the first of the big advances that transformed
the science of taxonomy. The second of his major achievements in this regard
occurred by accident. In 1753 he published a book called Species Plantarum
which was a list, organised according to the sexual system, of all the plants
known to Linnaeus at that time. It was essentially a flora of the world, a
field guide to the world's plants. In it he did something that was to
completely change the way in which things were named.
The birth of the binomial
Until that time, plants were being named with polynomial, Latin names. As
more and more species were being discovered, particularly in the
The binomial names were so much easier to remember that people soon
started using them in place of the 'correct' names. Eventually they replaced
the polynomial names completely, and became the correct names. The binomial
system is the same one we use today--it's how the scientific names of all
organisms are constructed. The first part of the name is called the genus and
is always capitalised. The second part of the name is called the species
epithet and is not capitalised. In the correct format of a scientific name a
person's name (sometimes abbreviated) appears after the genus and species name,
and this refers to the person who first coined the name. So the scientific name
for the raspberry, Rubus idaeus L., can be broken down like this: Rubus (the
genus name) idaeus (the species name) Linnaeus (the botanist who coined the
name, often abbreviated). Taxonomists have formulated sets of rules for naming;
all botanical naming begins with Linnaeus' Species Plantarum in 1753 and animal
naming with his tenth edition of Systema Naturae published in 1759.
Animals often reflect their physical attributes, which is useful in
aiding memory and providing a basic description. Sometimes those who attribute
the names make mistakes; Solanum arboreum sounds as if it should be a tree, but
is in fact a tiny shrub, which grows to only about
Names are also used to honour people. This practice can sometimes result
in cumbersome names; for example the plant Rahowardiana wardiana D'Arcy was
named by a mentor of mine, after two of his mentors, R.A. Howard and D.B. Ward.
Linnaeus was extremely fond of naming plants after people. He named the genus
Magnolia after the French Huguenot botanist Pierre Magnol, whom he greatly
respected, while the genus Sigesbeckia, a small creeping herb that grows in mud
was named for Linnaeus' main critic, Johann Siegesbeck, with whom Linneaus
quarrelled.
Cladistics and collections
Science involves a great deal of expertise. For a long time ideas about
the relationships that were believed to exist between groups of plants and
animals, that had been long-established by the scientific authorities of the
day, were rarely challenged. Whoever was the expert had the last word. In the
first decades of the twentieth century, a new generation of taxonomists started
to question the accepted dogma, and suggest alternatives.
Testing hypotheses
In the 1930s a German entomologist named Willi Hennig started developing
an entirely new way of looking at relationships. His work was to change the way
taxonomists work and still influences the way research is done today. Hennig
proposed the practice of taxonomy as a series of tests of hypotheses. For
example, three hypotheses could be applied to a group of three species, say the
coelacanth, the lungfish, and a salamander:
A taxonomist would call this a three-taxon statement--the simplest set
of hypotheses possible. To uphold or falsify the hypotheses, the taxonomist
would amass evidence in support of or against them by looking at the organisms'
characteristics--a term shortened to 'characters'.
The characters are each assigned a number. If say, character number one
is present in all three species under study, A, B and C, while character two is
present in species A and B and absent in species C; the taxonomist can define a
group of A+B based on the distribution of character two. Character distribution
can be mapped for all the species being studied, and
this distribution can reveal groupings of species that are more closely related
to each other than to anything else under study. Species and characters can be
added to the study, and this method makes taxonomy--the relationship
determining part of it--repeatable and shows others how the researcher arrived
at their conclusions about taxonomy.
This methodology allows taxonomists to identify two types of groups of
species. One type includes all the descendants of a common ancestor and is
known as a monophyletic group. The other type, known as a paraphyletic group,
includes most, but not all of the descendants of a common ancestor. A third
type of group is the polyphyletic group, where the members do not share a
common ancestor. With Hennig's developments, the task of taxonomy became to
identify the monophyletic groups by defining species' characters unambiguously
and plotting their distribution.
Cladistics
This new way of doing taxonomy was called cladistics. The word
cladistics comes from clade, itself derived from the Greek word for branch. A
clade is a group of organisms that share characters, and by extension, a common
ancestor. Clades are monophyletic groups. Cladistics meant that scientists no
longer relied on the gospel according to scientific authority. Now they were
able to look at groups of organisms, study their characters and suggest
alternative hypotheses.
In this way, an alternative hypothesis regarding the position of green
algae in relation to other plants was suggested. Green algae were always
considered to be a discrete and coherent group, all closely related to each
other and relatively distantly related to land plants. But analysis of the
distribution of certain characters such as type of cell division and
microtubule organization revealed that the green algae are an artificial,
paraphyletic, group. Despite superficial similarities, some members of the
group are much more closely related to land plants than they are to other green
algae.
Cladistics challenged the method of doing taxonomy that had been
accepted without question for a very long time. In the 1960's when Hennig's
book Phylogenetic Systematics (it was published in
Collecting and collections
The most important elements of taxonomy are the specimens themselves,
many held in museums and collections around the world. As well as relying on
collections, taxonomists often go out into the field to find new organisms and
collect specimens, and to see plants and animals in their native habitats. When
plants are collected they are pressed in newspaper and dried--in the same way
as traditional flower pressing. They are then mounted on paper so that they can
be studied. Plant specimens from high up in trees are often collected with pole
clippers, similar to those used by tree surgeons. They have several extension
sections and are extremely efficient, but heavy to carry around. In some parts
of the world, scientists hire local people to climb trees for them to access
specimens. In other parts of the world, where the locals don't do this, the
scientists sometimes learn to do it themselves.
Entomologists sometimes collect insects in much the same way as their
predecessors did, using butterfly nets with very long poles. They now also use
a wide variety of mechanical methods of trapping insects, ranging from simple
pitfall traps to more complex light traps and even more complicated methods. The
Malaise trap consists of a netting frame that goes all the way to the ground. Insects
fly into the netting, and in an attempt to escape they go upwards to find
themselves in the peak of the tent. They are naturally attracted to the
daylight from the pale top of the tent but on approaching it, drop into a
bottle of alcohol. Workers often leave this sort of trap in a remote area for
up to a week, and in this way collect a wide diversity of insects, including
those which would never be trapped using a butterfly net. The jar of alcohol
and insects--a sort of insect 'sludge'--is then sorted to major groups, and
specimens are prepared in the usual way, by pinning. Some of the specimens
collected in this way are so tiny they need to be glued to a tiny cardboard
triangle through which the pin is inserted.
Specimens are prepared in much the same way that they always have been. Butterflies
and moths are pinned through the body and put into special spreading boards,
then their wings are spread flat out on boards, and then they are dried at
extremely low heat in an oven. Using this method the wings stay flat and spread
so the colour pattern can be clearly seen.
Taxonomy and technology
The technological advances of the twentieth century have made the
process of examining organisms' characters much easier. For example,
microscopes allow us to look at the shapes of chloroplasts, the bodies that
convert light into energy, in particular plant cells. But one of the most
significant innovations of all has been the scanning electron microscope. This
microscope uses an electron beam to produce magnifying power that allows the
viewer to count the bristles on an ant's nose, and to look inside the anthers
of plants at the pollen, which is often fantastically sculptured and species
specific in shape. Even plankton, microscopic marine organisms which were
previously thought to have no clearly visible external characteristics, display a huge variety of shapes and characters under the
revealing gaze of the scanning electron microscope.
Characteristics can also be studied at the cellular level. Extracts of
plant or animal material containing enzymes can be placed within an electric
field and different proteins will travel different distances. One can look at
the banding patterns of these different proteins and analyze which populations
share certain enzymes and how populations or species differ. This technique is
called allozyme electrophoresis, and can be extremely useful for detecting
hybridization in nature.
Banding patterns formed by chopped up DNA fragments from a fern.
An organism's interaction with its environment can also be helpful to
the taxonomist. Behaviour has also become very important in determining
taxonomic relationships and looking at how things are related to one another. Many
parasitic insects are host-specific and only parasitize a single other species
of plant or animal. Studying the behaviour of these interactions can give
insect taxonomists clues about relationships and about the evolution of this
peculiar way of life--parasitism.
The genetic code
One of the greatest technological revolutions of all has been the
invention of methods enabling scientists to look directly at the genetic code. The discovery of the shape and function of DNA allows
taxonomists to study the genes that code for the organism's characters.
Thinking point
Taxonomists of the past would be amazed to learn of the technologies
that modern day researchers have at their disposal, and the information that
those technologies reveal. Do you think that future developments will deepen
our understanding of taxonomy to a level that we could not conceive of today?
All cells have DNA in the nucleus and also in their organelles, the
small cellular components such as chloroplasts or mitochondria. All the DNA from plant cells for example, can be extracted,
then separated into bands of different density which correspond to the
different size genomes from different parts of the cell. One way of looking at
DNA is to take a sequence of DNA, say the chloroplast DNA, which is much
smaller than nuclear DNA, from the cells and chop it up with special enzymes. The
resulting fragments can then be examined in the same way as allozymes are in an
electric field. The banding patterns--the distribution of the bands--can be
studied to assess the relationships between different plant species.
Output of a DNA sequencer
All DNA is made up of four nucleotides (deoxyribonucleotides--hence the
abbreviation DNA); adenine (A) guanine (G), cytosine (C) and thymine (T). The
DNA double helix consists of pairs of nucelotide bases--A always pairs with T,
and G always pairs with C, which link the two strands together. Sequencers read
single stranded DNA--like people read a line of text in a book. Each amino acid
produced by living cells is coded for by a triplet of nucleotides; for example
TTG codes for the essential amino acid leucine, while a triple with a single
nucleotide difference, ATG, codes for methionine. Proteins that carry out cell
functions are made up of a specific sequence of amino acids. So the sequence of
the bases in the DNA has a direct link to the cellular machinery that allows
all organisms to develop, grow and live in their environments.
DNA sequencing
When single stranded DNA is put through an automated sequencer, the
computer produces output that looks like many overlapping lines. Each base
shows up as a different colour: thymine is red, guanine is black, adenine is
green and cytosine is blue. The peaks correspond to the presence of particular
nucleotides and from this a sequence--ATCGTTA for example--can be read. These
sequences need to be aligned to make sure they are all in the correct 'reading
frame'.
Sequencing, however, is not the end of the story. To determine
relationships between organisms is much more complicated than that. Patterns
and sequences are sometimes extremely complex and can mislead the researcher. For
example, some plants from the tobacco genus Nicotiana show two phylogenetic
trees, one constructed using a sequence of DNA from the nucleus and the other a
sequence from the chloroplast genome. Chloroplasts in plants are inherited
maternally--so the paternal genome never shows up in a tree based on
chloroplast sequences. Nicotiana contains many species that are of hybrid
origin and are allopolyploid--they have twice the normal number of chromosomes,
a set from one of each parent. The trees based on chloroplast and nuclear
sequences conflict due to hybridity--if we did not know these species were of
hybrid origin, we would be seriously confused!
Many patterns seen at the DNA level are still not understood. For
example sometimes genes convert one to another or only one parental type is
inherited. Nicotiana tabacum, which is cultivated tobacco, is a tetraploid
hybrid species, with two sets of chromosome pairs--its two parents are
different diploid species, each with one set of chromosome pairs. It inherits
the chloroplast genes only from the maternal parent, Nicotiana sylvestris, and
so it groups with that species on the tree based on chloroplast sequences. Tobacco
groups with its paternal parent, Nicotiana tomentosiformis, on the tree based
on nuclear sequences. But nuclear sequence /paternal, chloroplast sequences /maternal
is not always the pattern seen. Sometimes, both sets of sequences group a
hybrid species with its mother and complicated patterns can result. So
sequencing does not provide all the answers as was originally hoped.
The genomes of some species have been sequenced completely. The only
plant to have had its entire genome sequenced so far is Arabidopsis thaliana, a
humble little weed in the mustard family with very simple flowers. The taxonomy
of Arabidopsis is not yet well understood, despite us knowing all about this
one species. To really determine relationships and study evolutionary patterns
in nature, we must know about more than one thing. Ideally one would need three
characters, to construct a three taxon hypothesis as described earlier.
Botanical taxonomists have long been interested in the development of
flowers because many sexual characters, which are found in the flowers, are
used to classify plants. Researchers are now looking at the genes that control
flower development, at the ways they are turned on and off and how they relate
to each other. What is being sought is essentially the genetic basis for what
Linnaeus called the sexual system over 300 years ago.
The future of taxonomy
These are exciting times for taxonomy. New techniques are being
developed all the time, and these often throw up as
many questions as provide answers.
Thinking point
How important is the science of taxonomy? Would the conservation of
biodiversity be possible without the information provided by taxonomists?
Taxonomy's challenges for tomorrow relate to the two threads that
construct its fabric--to name and identify species and to determine the
relationships between them--with the aim of ultimately understanding how
nature's wild, wonderful diversity is generated. During the science's history,
while new ways of looking at characters and methods of depicting relationships
have been developed, many new species have continued to be discovered. Linneaus
knew of 23 species of Solanum, the plant genus to which the potato and tomato
belong, in 1753. By 1852 the next Solanum monograph, compiled by a French
botanist working in
While ideas about relationships are changing, and new species being
described, the world around us is constantly changing. It sometimes changes for
the better, but more often for the worse. Deforestation and habitat destruction
are immense problems on a global scale. For example,
In 1992, world leaders attended the Earth Summit in
Biodiversity and the role of taxonomy
As the world becomes increasingly urban and globalised, people become
disconnected from the natural world around them. To conserve diversity we need
to also be able to develop some sort of feeling for it. In
Biodiversity is the term given to the variety of life on Earth and the
natural patterns it forms. Present biodiversity is the fruit of billions of
years of evolution, shaped by natural processes and, increasingly, by the
influence of humans. It forms the web of life of which we are an integral part
and upon which we so fully depend. This diversity is often understood in terms
of the wide variety of speices on Earth. So far, about 1.75 million species
have been identified, mostly small creatures such as insects. Scientists reckon
that there are actually about 13 million species, though estimates range from 3
to 100 million. Biodiversity also includes genetic differences within each
species, for example, between varieties of crops and breeds of livestock. Chromosomes,
genes, and DNA--the building blocks of life--determine the uniqueness of each
individual and each species.
Yet another aspect of biodiversity is the variety of ecosystems such as
those that occur in deserts, forests, wetlands, mountains, lakes, and
agricultural landscapes. In each ecosystem, living creatures, including humans,
form a community, interacting with one another and with the air, water and soil
around them. It is the combination of life forms and their interactions with
each other and with their environment that has made Earth a uniquely habitable
place for humans.
Taxonomy's role is vital, because without taxonomists documenting the
natural world, we no longer have the fabric that underpins not only biology,
but also the science of conservation. Taxonomy is a science that keeps pace
with the present but also draws upon the wealth of knowledge accumulated
throughout its history. At the same time it is constantly making advances, and
looking at organisms and their characters in new and ever more creative ways. Who
knows what the next generation of characters will be?
Taxonomy in the twenty first century will seem completely different than
that of the past--but like good fabric, it still retains both of its threads. Taxonomists
do not discard their past, but build upon it in ever more creative ways. While
retaining our past, we look forward to increased relevance, both to society at
large through our participation in global efforts to conserve the world in
which we live, and scientifically, as we refine ever further our hypotheses
about life itself. But being a taxonomist today is more difficult than it has
ever been--you need to be able to drive both a jeep and an automatic sequencer--but
sadly, we are a shrinking community, perhaps as endangered as the organisms we
study.
But the future is not bleak--linkages between science and society mean
that the role of taxonomy is becoming more appreciated now than ever before. We
still have a lot to do, even more so now than when Alfred Russel Wallace penned
these somewhat prophetic words:
… the most perfect
collections possible in every branch of natural history should be made and
deposited in national museums, where they may be available for study and
interpretation.
If this is not done, future ages will certainly look back upon us as a
people so immersed in the pursuit of wealth as to be blind to higher
considerations. They will charge us with culpably allowing the destruction of [that]
which we had it in our power to preserve; and while professing to regard every
living thing as the direct handiwork and best evidence of a Creator, yet, with
a strange inconsistency, seeing many of them perish irrecoverably from the face
of the earth, uncared for and unknown.