30 The Meaning of Biodiversity and the Tree of Life

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Edward O. Wilson

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It seems very likely, in accordance with the belief of many

anthropologists, that the first words to emerge during the

evolution of human speech were used to specify people,

plants, animals, and other objects, a roster that proliferated

rapidly thereafter. That step, which presumably occurred

sometime during the transition from Homo erectus to Homo

sapiens a half million years ago, can rightfully be considered

the earliest roots of science. Accuracy and repeatability

were vital for the sake of survival, then as now. Getting

things by their right names, as the Chinese say, is the first

step to wisdom.

And so it came to pass that the emergence of modern

Western science included an effort to name the immense

array of plant and animal species on Earth, and also to group

them in a system that reflects their degree of similarity. That

was an eighteenth-century achievement, culminating in the

binomial nomenclatural system of the Swedish naturalist

Carolus Linnaeus. Scientific taxonomy was followed by the

notion of a genealogy of species, a nineteenth-century advance

foreshadowed by the acceptance of evolution. In the

twentieth century came the explanation of the process of

species multiplication, one of the central achievements of the

Modern Synthesis of evolutionary theory.

And now what? The answer, clearly, is a complete account

of Earth’s biodiversity, pole to pole, bacteria to whales, at

every level of organization from genome to ecosystem, yielding

as complete as possible a cause-and-effect explanation

of the biosphere, and a correct and verifiable family tree for

all the millions of species—in short, a unified biology. That

vision, I presume, is widely shared, and why we are here.

Let me put this shared conception another way: we are

here to reassert the rightful place of systematics in the mainstream

of biology. In recent decades, as the molecular revolution

swept over biology like a tidal wave, systematics sank

in esteem. It was, in the view of the molecular triumphalists,

old-fashioned biology. To many of them, its subject matter

seemed spent, its practitioners dull and pedestrian. Professional

taxonomists did not actually decline in population

during this Dark Age, but their number, which is about 6000

worldwide today, fell sharply in relation to the total of scientists,

of which perhaps half a million or more work in the

United States alone. The total support given systematics research

nationally from all sources, including museums, universities,

and government agencies, is still a miserly $150 to

$200 million annually.

But the problem with systematics, including primary

descriptive taxonomy devoted to new species and monographs

of those previously classified, was never obsolescence.

The problem with systematics was the failure to recognize

its true importance.

Consider, for example, the primary exploration of the

biosphere. We do not know even to the nearest order of

magnitude the number of living species on Earth. Estimates

of the total number vacillate wildly according to method.

They range from 3.6 million at the low end to more than 100

million at the high end. The estimated number of species of

540 Perspectives on the Tree of Life

all kinds of organisms—plants, animals, and microorganisms—

formally described with scientific names falls somewhere

between 1.5 and 8 million, but a complete and careful

census remains to be made. In short, we lack even an exact

accounting of what we already know.

The following figures will give you an idea of how far

we have to go in purely descriptive alpha taxonomy. About

69,000 species of fungi have been identified and named, but

as many as 1.6 million are thought to exist. Of the nematode

worms, making up four of every five animals on Earth—creatures

so abundant that if all other matter on the surface of

the planet were to disappear it is said you could still see the

ghostly outline of most of it in nematodes—some 15,000

species are known but millions more may await discovery.

The truth is that we have only begun to explore life on

Earth. The gap in knowledge is maximum in the case of the

bacteria and the outwardly similar archaeans, the black hole

of systematics, whose species could number in the tens of

thousands or, with equal ease, in the tens of millions. Our

ignorance of these microorganisms is epitomized by bacteria

of the genus Prochlorococcus, arguably the most abundant

organisms on the planet, and responsible for a large part of

the organic production of the ocean, yet unknown to science

until 1988. Prochlorococcus cells float passively in open water

at 70,000–200,000 per milliliter, multiplying with energy

captured from sunlight. Their extremely small size is what

makes them so elusive. They belong to a special group called

picoplankton, simple-celled organisms much smaller than

conventional bacteria and barely visible at the highest optical

magnification.

Even figures for the relatively well-studied vertebrates are

spongy. Estimates for the living fish species of the world,

including those both described and undescribed, range from

15,000 to 40,000. The global number of described and

named amphibian species, including frogs, toads, salamanders,

and the less familiar caecilians, has grown in the

past 15 years by one-third, from 4000 to 5300 at this moment.

In the same period of time the number of known mammals

has also jumped from about 4000 to 5000. And

similarly, the flowering plants, for centuries among the favorite

targets of field biologists, contain significant pockets

of unexplored diversity. About 272,000 species have been

described worldwide, but the true number is certain to be

more than 300,000, because each year about 2000 new species

are added to the world list published in the standard

Index Kewensis (available at http://www.ipni.org/).

You will recognize the following image in popular fiction:

a scientist discovers a new species of animal or plant somewhere

in the upper Amazon. At base camp the team celebrates

and sends the good news back to the home institution. Mention

of the event is made somewhere in the New York Times.

The truth, I assure you, is radically different. Scientists expert

in the classification of each of the most diverse groups,

such as bacteria, fungi, and insects, are continuously burdened

with new species almost to the breaking point. Working

mostly alone and on minuscule budgets, they try desperately

to keep their collections in order while eking out

enough time to publish accounts of a small fraction of the

novel life forms sent to them for identification.

Many systematists share this experience, of which my

own example and those of fellow myrmecologists have been

typical. About 11,000 species of ants have been named, but

that number, we believe, is likely to double when tropical

regions are more fully explored. While recently conducting

a study of Pheidole, one of the world’s two largest ant genera,

I uncovered 340 new species, more than doubling the number

in the genus and increasing the entire known fauna of

ants in the Western Hemisphere by 20%. When my monograph

was published in the spring of 2003, additional new

species were still pouring in, mostly from collectors working

in the tropics.

Why should we work so hard to complete the Linnaean

enterprise? The answer is simple and compelling. To describe

and to classify all of the surviving species of the world deserves

to be one of the great scientific goals of the new century.

In applied science, it is needed for effective conservation

of natural resources, for bioprospecting (i.e., the search for

new classes of pharmaceuticals and other natural products

in wild species), and for impact studies of environmental

change. In basic science, a complete biodiversity map is a key

element in the advancement of ecology, including especially

the understanding of ecosystem assembly and functioning.

In reconstructing the Tree of Life, the new Linnaean enterprise

is fundamental to genetics and evolutionary biology.

Not least, it also offers an unsurpassable adventure: the exploration

of a little-known planet.

Biodiversity exploration is the cutting edge of a still

greater effort. Natural history remains far behind descriptive

taxonomy. Of the named species—never mind those still

undiscovered—fewer than 1% have been studied beyond the

essentials of habitat preference and diagnostic anatomy. In

addressing complex natural systems, ecologists and conservation

biologists appear not to fully appreciate how thin is

the ice on which they skate.

When large arrays of species are studied in depth for their

intrinsic interest, the result is a surge in basic and applied

research in other domains of biology. New phenomena are

discovered and research agendas suggested that had never

been conceived by researchers focused on favored single

species such as Escherichia coli and Homo sapiens.

The complete census of Earth’s biodiversity is no longer

a distant dream. It is buoyed by the information revolution.

New electronic technology, increasing exponentially in capacity

and user-friendliness, is trimming the cost and time

required for taxonomic description and data analysis. It

promises to speed traditional systematics by a hundred times

or more.

Within 10–20 years the combined methodology might

work as follows: imagine an arachnologist making the first

study of the spiders of an isolated rainforest in Ecuador.

The Meaning of Biodiversity and the Tree of Life 541

He sits in a camp sorting newly collected specimens

with the aid of a portable, internally illuminated

microscope. After quickly sorting the material to

family or genus, he enters the electronic keys that list

character states for, say, 20 characters and pulls out

the most probable names for each specimen in turn.

Now the arachnologist consults monographs of the

families or genera available on the World Wide Web,

studying the illustrations, pondering the distribution

maps and natural history recorded to date. If monographs

are not yet available, he calls up digitized

photographs from the central global biodiversity files

of the most likely type specimens taken wherever they

are—London, Vienna, Sгo Paulo, anywhere photographic

or electron micrographs have been made—and

compares them with the fresh specimens by panning,

rotating, magnifying, and pulling back again for

complete views. Perhaps he feeds an automatic

feature-matching program. Does this specimen belong

to a new species? He records its existence (noting the

exact location from his global positioning system

receiver), habitat, web form, and other relevant

information into the central files, and he states where

the voucher specimens will be placed—perhaps later

to become type specimens. Informatics has thus

allowed the type specimens of Ecuadorian spiders to

be electronically repatriated to Ecuador, and new data

on its spider fauna to be made immediately and

globally available.

The arachnologist has accomplished in a few hours what

previously consumed weeks or months of library and museum

research. He understands that biodiversity studies

advance along three orthogonal axes. First are monographs,

which treat all of the species across their entire ranges. Second

are local biodiversity studies, which describe in detail

the species occurring in a single locality, habitat, or region.

When expanded to include more and more groups, local

biodiversity studies may eventually cover all local plants,

animals, and microorganisms, creating an all-taxa biotic inventory,

a truly solid base for community ecology in its full

complexity.

The next step in global biodiversity mapping can be expected

to follow close behind, thanks to the swift advances

occurring in genomics. Already on the order of 10,000 species

from the major domains of organisms have been sequenced

for their small subunit ribosomal genes. As the

process accelerates, so will growth of these and other base

pair data, and in a reasonably short time the sequences will

become a standard tool for identification and phylogenetic

reconstruction across all groups of organisms.

Next on the horizon and coming up fast are complete

genomes and, in particular, those of functional genes. A

method has recently been conceived, using parallel sequencing

of single DNA or RNA strands through nanopores, that

if successful could read off the three billion base pairs of a

human cell in hours or the thousand or so of a virus in seconds.

Holes little more than a nanometer in width are

punched through cell membrane with staphylococcus bacteria,

forming channels just wide enough to thread single

strands of nucleotides but not double strands. Electrical

impulses force the strands through, and differences in conductance

of the base pairs identify them after passage. The

method is in an intermediate stage of development and may

not in the end become operable, but at the very least it illustrates

the potential of technologies, for example, those that

include advances in the shotgunning method, poised to advance

genomics and put it at the service of systematics and

the rest of biology.

Ultrafast genomic mapping is not necessary for the identification

of a butterfly or flowering plant. The larger and

anatomically more complex eukaryotic organisms can be

identified very swiftly by visual inspection of their diagnostic

phenotypes, if not in the heads of experts then by the use

of software that automatically scans specimens and their

images with a capacity for near-instantaneous matching and

identification. But rapid sequencing is crucial for viruses,

bacteria, fungi, and many of the smaller soft-bodied animals.

When microorganisms can be quickly identified by their

genomes, the impact on biology will be enormous. For the

first time a comprehensive picture of their diversity and geography

will emerge. Ambiguities concerning the root of the

Tree of Life will diminish as the earliest stages in the evolution

of life are more precisely defined. The origin and role of

natural transgenes in the early evolution of higher organisms

will be clarified. In ecology the effect will be truly revolutionary,

because microorganisms are a large part of the foundation

of ecosystems, yet to date are largely unstudied. It will

be possible to enter undisturbed ecosystems at micro and

nano levels, observe thousands of kinds of microorganisms

in action in the same way we now observe animals and plants

macroscopically, and from these miniature and still unexplored

rainforests of the ultrasmall, collect colonies and individuals

for rapid identification. I believe it safe to predict

that within 10–20 years, microbial systematics and microbial

ecology will become major industries of science.

In exploring large and microscopic organisms alike, the

grail of a global all-taxon biological inventory (ATBI) also seems

attainable within a matter of decades, say, in 20 years, if it is

made a scientific priority. The time has come to treat the global

ATBI as a near-horizon goal rather than, as traditional in

the past, an eventual destination. Above all, it is rendered urgent

by the accelerating worldwide destruction of natural ecosystems

and extinction of species. Conservation biologists are

in near-unanimous agreement that human activity has inaugurated

a mass extinction spasm not equaled since the end of

the Mesozoic era 65 million years ago. At the present rate of

environmental degradation, as many as a quarter of the stillexisting

plant and animal species could be gone or committed

to early extinction within 30 years, and half by the end of

542 Perspectives on the Tree of Life

the 21st century. Biology is the only science whose subject

matter is vanishing. Alerted to the technological advances that

promise to empower the global ATBI, and realizing the importance

of such a thorough survey for humanity, a dozen or

so groups around the world have initiated ATBIs on a continental

or global scale, and to varying degrees of resolution—

with or without microorganisms, for example, or based on

existing databases and museum specimens or not. One of the

most ambitious is the Global Biodiversity Information Facility

(GBIF for short), conceived within the Organisation for

Economic Co-operation and Development (OECD) in 1999,

headquartered this year in Copenhagen, and funded by

pledges from 14 OECD member countries. In 2001, another,

private organization, the All Species Foundation, was begun

in California with the same goal as the GBIF. That fall the All

Species Foundation hosted a summit meeting at Harvard of

organizations engaged in continental and global all-taxon censusing.

They included GBIF; the Association for Biodiversity

Information, which has been newly created from the Natural

Heritage Network of the Nature Conservancy; the Biodiversity

Foundation for Africa; and others.

In time such organizations will try to work out a plan for

concerted action, a timeline, a budget, a suite of methodologies,

and a fund-raising program that raises all ships. I expect

that a heavy emphasis will be put on the financial

support and upgrading of basic systematics research, including

straightforward alpha taxonomy, which, I trust you will

agree, undergirds everything we accomplish and hope to

accomplish in systematics generally.

The effort to complete a global biodiversity map is likely

to follow the following stages:

• First and foremost is the high-resolution imaging of

primary types of all species for which this is practicable

or, in absence of types, other authenticated

material.

• At the same time, or soon thereafter, with the

supervision of expert systematists, the images,

collection data, and bibliography references and

synonymy will be placed on the Internet.

• Then this vastly more accessible database will be used

to prepare monographs, field guides, and instructional

manuals at a greatly speeded-up pace.

• In the longer term, field exploration will pick up to

fill the gaps, yielding Internet diagnoses of new

species and expansion of databases for already known

species.

• Simultaneously, there will be ongoing phylogenetic

reconstructions of species, updated as novelties and

new data are added. The Tree of Life, including the

interpretation of the evolutionary history of all living

taxa and the antecedent taxa recoverable by cladistic

inference and the fossil record, will emerge with

constantly improving clarity.

• Finally, a true encyclopedia of life will be pieced

together, transiting all levels of biological organization,

genome to ecosystem, and enlarged continuously

during the generations to come.

In visualizing the universal tree, the living species can be

thought of as the growing tips of the twigs and leaves, and

their antecedents the branches. The living species are monitored

in organismic and evolutionary time, the intervals of

which witness changes that can be observed within a human

generation. The histories of the branches, in contrast, are

reconstructed in evolutionary time, across intervals that in

most cases extend deep into geological history.

Systematists who work on living species, the twigs and

leaves of the Tree of Life, produce information increasingly

vital to the rest of biology, from molecular and cell biology

and the medical sciences to ecology and conservation biology.

Those who work on phylogeny, the branching patterns

across evolutionary time, provide the basis of a sound higher

classification and our integrated picture of the history of life.

Exploratory systematics and phylogenetic reconstruction are

synergistic, reinforcing one another, illuminating biodiversity

as it is in this instant of geological time and tracing its origins

through deep geological time.

From the alpha taxonomy of species and geographical

races to their phylogeny, modern systematics becomes at last

a seamless web of rigorous science and cutting-edge technology.

Applied to each level of biological organization in turn,

it is the key to a unified biology.

In other chapters of this volume are dispatches from the

front delivered by some of our leading authorities on the

systematics and evolution of virtually the complete spread

of biodiversity. They will make clear that in drawing the Tree

of Life, from the still tangled and problematic trunk of bacteria

and archaeans to the mind-boggling productions of the

flowering plants and animals, a new biology is emerging. They

will establish, I am confident, that systematics is what ties

biology together. Implicit also will be the necessity of this

knowledge for the preservation of Earth’s fauna and flora,

including that awkwardly bipedal, bulge-headed, tool-making,

incessantly chattering Old World primate species, Homo

sapiens. The universal ATBI and the unified Tree of Life are

the conceptions that will surely fire the ambition and release

the energies of those committed to evolutionary biology.

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