92 S C I E N T I F I C A M E R I C A N R e p r i n t e d f r.docx

92 S C I E N T I F I C A M E R I C A N R e p r i n t e d f r o
m t h e O c t o b e r 1 9 9 4 i s s u e
ome creators announce their inventions with grand
éclat. God proclaimed, “Fiat lux,” and then flooded
his new universe with brightness. Others bring forth
great discoveries in a modest guise, as did Charles
Darwin in defining his new mechanism of evolu-
tionary causality in 1859: “I have called this principle, by
which
each slight variation, if useful, is preserved, by the term Natur-
al Selection.”
Natural selection is an immensely powerful yet beautifully
simple theory that has held up remarkably well, under intense
and unrelenting scrutiny and testing, for 135 years. In essence,
natural selection locates the mechanism of evolutionary change
in a “struggle” among organisms for reproductive success, lead-
ing to improved fit of populations to changing environments.
(Struggle is often a metaphorical description and need not be
viewed as overt combat, guns blazing. Tactics for reproductive
success include a variety of nonmartial activities such as earlier
and more frequent mating or better cooperation with partners
in raising offspring.) Natural selection is therefore a principle
of
local adaptation, not of general advance or progress.
Yet powerful though the principle may be, natural selection
is not the only cause of evolutionary change (and may, in many
cases, be overshadowed by other forces). This point needs em-
phasis because the standard misapplication of evolutionary the-

ory assumes that biological explanation may be equated with
devising accounts, often speculative and conjectural in practice,
about the adaptive value of any given feature in its original en-
vironment (human aggression as good for hunting, music and
religion as good for tribal cohesion, for example). Darwin him-
self strongly emphasized the multifactorial nature of evolu-
tionary change and warned against too exclusive a reliance on
natural selection, by placing the following statement in a max-
imally conspicuous place at the very end of his introduction: “I
am convinced that Natural Selection has been the most impor-
tant, but not the exclusive, means of modification.”
Reality versus Conceit
N A T U R A L S E L E C T I O N is not fully sufficient to
explain evo-
lutionary change for two major reasons. First, many other caus-
es are powerful, particularly at levels of biological organization
both above and below the traditional Darwinian focus on or-
ganisms and their struggles for reproductive success. At the
low-
est level of substitution in individual base pairs of DNA, change
is often effectively neutral and therefore random. At higher lev-
els, involving entire species or faunas, punctuated equilibrium
can produce evolutionary trends by selection of species based
on their rates of origin and extirpation, whereas mass extinc-
tions wipe out substantial parts of biotas for reasons unrelat-
ed to adaptive struggles of constituent species in “normal”
times between such events.
Second, and the focus of this article, no matter how ade-
quate our general theory of evolutionary change, we also yearn
to document and understand the actual pathway of life’s his-
tory. Theory, of course, is relevant to explaining the pathway
(nothing about the pathway can be inconsistent with good the-
ory, and theory can predict certain general aspects of life’s geo-

logic pattern). But the actual pathway is strongly underdeter-
mined by our general theory of life’s evolution. This point
needs
some belaboring as a central yet widely misunderstood aspect
of the world’s complexity. Webs and chains of historical events
are so intricate, so imbued with random and chaotic elements,
so unrepeatable in encompassing such a multitude of unique
(and uniquely interacting) objects, that standard models of sim-
ple prediction and replication do not apply.
The history of life is not necessarily progressive; it is certainly
not predictable. The earth’s creatures have evolved through
a series of contingent and fortuitous events
evolution of
life on earth
By Stephen Jay Gould
S
the
COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC.
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w w w . s c i a m . c o m S C I E N T I F I C A M E R I C A N
93
History can be explained, with satisfying rigor if evidence be
adequate, after a sequence of events unfolds, but it cannot be
pre-
dicted with any precision beforehand. Pierre-Simon Laplace,
echoing the growing and confident determinism of the late 18th
century, once said that he could specify all future states if he
could
know the position and motion of all particles in the cosmos at
any moment, but the nature of universal complexity shatters this
chimerical dream. History includes too much chaos, or
extremely
sensitive dependence on minute and unmeasurable differences
in
initial conditions, leading to massively divergent outcomes
based
on tiny and unknowable disparities in starting points. And his-
tory includes too much contingency, or shaping of present
results
by long chains of unpredictable antecedent states, rather than
im-
mediate determination by timeless laws of nature.
Homo sapiens did not appear on the earth, just a geologic
second ago, because evolutionary theory predicts such an out-
come based on themes of progress and increasing neural com-
plexity. Humans arose, rather, as a fortuitous and contingent
outcome of thousands of linked events, any one of which could
have occurred differently and sent history on an alternative
pathway that would not have led to consciousness. To cite just
four among a multitude: (1) If our inconspicuous and fragile
lin-
eage had not been among the few survivors of the initial radia-

tion of multicellular animal life in the Cambrian explosion 530
million years ago, then no vertebrates would have inhabited the
earth at all. (Only one member of our chordate phylum, the
genus Pikaia, has been found among these earliest fossils. This
small and simple swimming creature, showing its allegiance to
us by possessing a notochord, or dorsal stiffening rod, is among
the rarest fossils of the Burgess Shale, our best preserved Cam-
brian fauna.) (2) If a small and unpromising group of lobe-
finned fishes had not evolved fin bones with a strong central
axis
capable of bearing weight on land, then vertebrates might nev-
er have become terrestrial. (3) If a large extraterrestrial body
had not struck the earth 65 million years ago, then dinosaurs
would still be dominant and mammals insignificant (the situa-
tion that had prevailed for 100 million years previously). (4) If
a small lineage of primates had not evolved upright posture on
the drying African savannas just two to four million years ago,
then our ancestry might have ended in a line of apes that, like
the chimpanzee and gorilla today, would have become ecolog-
ically marginal and probably doomed to extinction despite their
remarkable behavioral complexity.
Therefore, to understand the events and generalities of life’s
pathway, we must go beyond principles of evolutionary theory
to a paleontological examination of the contingent pattern of
life’s history on our planet—the single actualized version
among
millions of plausible alternatives that happened not to occur.
Such a view of life’s history is highly contrary both to conven-
tional deterministic models of Western science and to the deep-
est social traditions and psychological hopes of Western culture
for a history culminating in humans as life’s highest expression
and intended planetary steward.
Science can, and does, strive to grasp nature’s factuality, but

all science is socially embedded, and all scientists record pre-
vailing “certainties,” however hard they may be aiming for pure
objectivity. Darwin himself, in the closing lines of On the Ori-
gin of Species, expressed Victorian social preference more than
SLAB CONTAINING SPECIMENS of Pteridinium from
Namibia shows a
prominent organism from the earth’s first multicellular fauna,
called
Ediacaran, which appeared some 600 million years ago. The
Ediacaran
animals died out before the Cambrian explosion of modern life.
These thin,
quilted, sheetlike organisms may be ancestral to some modern
forms but
may also represent a separate and ultimately failed experiment
in
multicellular life. The history of life tends to move in quick and
quirky
episodes, rather than by gradual improvement.
nature’s record in writing: “As natural
selection works solely by and for the
good of each being, all corporeal and
mental endowments will tend to progress
towards perfection.”
Life’s pathway certainly includes
many features predictable from laws of
nature, but these aspects are too broad
and general to provide the “rightness”

that we seek for validating evolution’s
particular results—roses, mushrooms,
people and so forth. Organisms adapt to,
and are constrained by, physical princi-
ples. It is, for example, scarcely surpris-
ing, given laws of gravity, that the largest
vertebrates in the sea (whales) exceed the
heaviest animals on land (elephants to-
day, dinosaurs in the past), which, in
turn, are far bulkier than the largest ver-
tebrate that ever flew (extinct pterosaurs
of the Mesozoic era).
Predictable ecological rules govern the
structuring of communities by principles
of energy flow and thermodynamics
(more biomass in prey than in predators,
for example). Evolutionary trends, once
started, may have local predictability
(“arms races,” in which both predators
and prey hone their defenses and weap-
ons, for example—a pattern that Geerat
J. Vermeij of the University of California
at Davis has called “escalation” and doc-
umented in increasing strength of both
crab claws and shells of their gastropod
prey through time). But laws of nature do
not tell us why we have crabs and snails
at all, why insects rule the multicellular
world and why vertebrates rather than
persistent algal mats exist as the most
complex forms of life on the earth.
Relative to the conventional view of
life’s history as an at least broadly pre-

dictable process of gradually advancing
complexity through time, three features
of the paleontological record stand out in
opposition and shall therefore serve as
organizing themes for the rest of this ar-
ticle: the constancy of modal complexity
throughout life’s history; the concentra-
tion of major events in short bursts inter-
spersed with long periods of relative sta-
bility; and the role of external impositions,
primarily mass extinctions, in disrupting
patterns of “normal” times. These three
features, combined with more general
themes of chaos and contingency, require
a new framework for conceptualizing
and drawing life’s history, and this article
therefore closes with suggestions for a dif-
ferent iconography of evolution.
The Lie of “Progress”
T H E P R I M A R Y paleontological fact
about life’s beginnings points to pre-
dictability for the onset and very little for
the particular pathways thereafter. The
earth is 4.6 billion years old, but the old-
est rocks date to about 3.9 billion years
because the earth’s surface became molten
early in its history, a result of bombard-
ment by large amounts of cosmic debris
during the solar system’s coalescence and
of heat generated by radioactive decay of
short-lived isotopes. These oldest rocks
are too metamorphosed by subsequent
heat and pressure to preserve fossils (al-
though some scientists interpret the pro-

portions of carbon isotopes in these
rocks as signs of organic production).
The oldest rocks sufficiently unaltered to
retain cellular fossils—African and Aus-
tralian sediments dated to 3.5 billion
years old—do preserve prokaryotic cells
(bacteria and cyanophytes) and stroma-
tolites (mats of sediment trapped and
bound by these cells in shallow marine
waters). Thus, life on the earth evolved
quickly and is as old as it could be. This
fact alone seems to indicate an inevit-
ability, or at least a predictability, for
life’s origin from the original chemical
constituents of atmosphere and ocean.
No one can doubt that more com-
plex creatures arose sequentially after
this prokaryotic beginning—first eu-
karyotic cells, perhaps about two billion
years ago, then multicellular animals
about 600 million years ago, with a relay
of highest complexity among animals
passing from invertebrates, to marine
vertebrates and, finally (if we wish, albeit
parochially, to honor neural architecture
as a primary criterion), to reptiles, mam-
mals and humans. This is the conven-
tional sequence represented in the old
charts and texts as an “age of inverte-
brates,” followed by an “age of fishes,”
“age of reptiles,” “age of mammals,”
and “age of man” (to add the old gender
bias to all the other prejudices implied by
this sequence).

I do not deny the facts of the preced-
ing paragraph but wish to argue that our
conventional desire to view history as
progressive, and to see humans as pre-
dictably dominant, has grossly distorted
our interpretation of life’s pathway by
falsely placing in the center of things a
relatively minor phenomenon that arises
only as a side consequence of a physical-
ly constrained starting point. The most
salient feature of life has been the stabil-
ity of its bacterial mode from the begin-
94 S C I E N T I F I C A M E R I C A N D I N O S A U R S A
N D O T H E R M O N S T E R S
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PROGRESS DOES NOT RULE (and is not even a primary thrust
of) the evolutionary process. For reasons

of chemistry and physics, life arises next to the “left wall” of its
simplest conceivable and preservable
complexity. This style of life (bacterial) has remained most
common and most successful. A few
creatures occasionally move to the right, thus extending the
right tail in the distribution of
complexity. Many always move to the left, but they are
absorbed within space already occupied.
Note that the bacterial mode has never changed in position, but
just grown higher.
Left wall of minimal complexity
Bacteria
Complexity
Present
Precambrian
Fr
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Bacteria
ning of the fossil record until today and,
with little doubt, into all future time so
long as the earth endures. This is truly the
“age of bacteria”—as it was in the be-
ginning, is now and ever shall be.
For reasons related to the chemistry
of life’s origin and the physics of self-
organization, the first living things arose
at the lower limit of life’s conceivable,
preservable complexity. Call this lower
limit the “left wall” for an architecture of
complexity. Because so little space exists
between the left wall and life’s initial bac-
terial mode in the fossil record, only one
direction for future increment exists—to-
ward greater complexity at the right.
Thus, every once in a while, a more com-
plex creature evolves and extends the
range of life’s diversity in the only avail-
able direction. In technical terms, the dis-
tribution of complexity becomes more
strongly right skewed through these oc-
casional additions.
But the additions are rare and epi-
sodic. They do not even constitute an evo-

lutionary series but form a motley se-
quence of distantly related taxa, usually
depicted as eukaryotic cell, jellyfish, trilo-
bite, nautiloid, eurypterid (a large relative
of horseshoe crabs), fish, an amphibian
such as Eryops, a dinosaur, a mammal
and a human being. This sequence can-
not be construed as the major thrust or
trend of life’s history. Think rather of an
occasional creature tumbling into the
empty right region of complexity’s space.
Throughout this entire time, the bacteri-
al mode has grown in height and re-
mained constant in position. Bacteria rep-
resent the great success story of life’s path-
way. They occupy a wider domain of
environments and span a broader range
of biochemistries than any other group.
They are adaptable, indestructible and
astoundingly diverse. We cannot even
imagine how anthropogenic intervention
might threaten their extinction, although
we worry about our impact on nearly
every other form of life. The number of
Escherichia coli cells in the gut of each hu-
man being exceeds the number of hu-
mans that has ever lived on this planet.
One might grant that complexifica-
tion for life as a whole represents a
pseudotrend based on constraint at the
left wall but still hold that evolution with-
in particular groups differentially favors
complexity when the founding lineage
begins far enough from the left wall to

permit movement in both directions. Em-
pirical tests of this interesting hypothesis
are just beginning (as concern for the sub-
ject mounts among paleontologists), and
we do not yet have enough cases to ad-
vance a generality. But the first two stud-
ies—by Daniel W. McShea of the Uni-
versity of Michigan on mammalian ver-
tebrae and by George F. Boyajian of the
University of Pennsylvania on ammonite
suture lines—show no evolutionary ten-
dencies to favor increased complexity.
Moreover, when we consider that for
each mode of life involving greater com-
plexity, there probably exists an equally
advantageous style based on greater sim-
plicity of form (as often found in para-
sites, for example), then preferential evo-
lution toward complexity seems unlikely
a priori. Our impression that life evolves
toward greater complexity is probably
only a bias inspired by parochial focus on
ourselves, and consequent overattention
to complexifying creatures, while we ig-
nore just as many lineages adapting
equally well by becoming simpler in
form. The morphologically degenerate
parasite, safe within its host, has just as
much prospect for evolutionary success
as its gorgeously elaborate relative cop-
ing with the slings and arrows of outra-
geous fortune in a tough external world.
Steps, Not Inclines

E V E N I F C O M P L E X I T Y is only a drift
away from a constraining left wall, we
might view trends in this direction as
more predictable and characteristic of
life’s pathway as a whole if increments of
complexity accrued in a persistent and
gradually accumulating manner through
time. But nothing about life’s history is
more peculiar with respect to this com-
mon (and false) expectation than the ac-
tual pattern of extended stability and
rapid episodic movement, as revealed by
the fossil record.
Life remained almost exclusively uni-
cellular for the first five sixths of its his-
tory—from the first recorded fossils at
3.5 billion years to the first well-doc-
umented multicellular animals less than
w w w . s c i a m . c o m S C I E N T I F I C A M E R I C A N
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NEW ICONOGRAPHY OF LIFE’S TREE shows that maximal
diversity in anatomical forms (not in number
of species) is reached very early in life’s multicellular history.
Later times feature extinction of most
of these initial experiments and enormous success within
surviving lines. This success is measured
in the proliferation of species but not in the development of new
anatomies. Today we have more
species than ever before, although they are restricted to fewer
basic anatomies.
Anatomical Diversity
Ti
m
e
STEPHEN JAY GOULD taught biology, geology and the history
of science at Harvard Uni-
versity from 1967 until his death in 2002 at age 60. The
influential and provocative evo-
lutionary biologist had a Ph.D. in paleontology from Columbia
University. Well known for
his popular writings, in particular a monthly column in Natural
History magazine, he was
the author of more than a dozen books, including Full House:
The Spread of Excellence from
Plato to Darwin and The Mismeasure of Man. T
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600 million years ago. (Some simple
multicellular algae evolved more than a
billion years ago, but these organisms be-
long to the plant kingdom and have no
genealogical connection with animals.)
This long period of unicellular life does
include, to be sure, the vitally important
transition from simple prokaryotic cells
without organelles to eukaryotic cells
with nuclei, mitochondria and other com-
plexities of intracellular architecture—
but no recorded attainment of multicel-
lular animal organization for a full three
billion years. If complexity is such a good
thing, and multicellularity represents its
initial phase in our usual view, then life
certainly took its time in making this cru-
cial step. Such delays speak strongly
against general progress as the major
theme of life’s history, even if they can be
plausibly explained by lack of sufficient
atmospheric oxygen for most of Precam-

brian time or by failure of unicellular life
to achieve some structural threshold act-
ing as a prerequisite to multicellularity.
More curiously, all major stages in or-
ganizing animal life’s multicellular archi-
tecture then occurred in a short period be-
ginning less than 600 million years ago
and ending by about 530 million years
ago—and the steps within this sequence
are also discontinuous and episodic, not
gradually accumulative. The first fauna,
called Ediacaran to honor the Australian
locality of its initial discovery but now
known from rocks on all continents, con-
sists of highly flattened fronds, sheets and
circlets composed of numerous slender
segments quilted together. The nature of
the Ediacaran fauna is now a subject of
intense discussion. These creatures do not
seem to be simple precursors of later
forms. They may constitute a separate
and failed experiment in animal life, or
34. Sidneyia
35. Odaraia
36. Eiffelia
37. Mackenzia
38. Odontogriphus
39. Hallucigenia
40. Elrathia
41. Anomalocaris
42. Lingulella
43. Scenella
44. Canadaspis

45. Marrella
46. Olenoides
22. Emeraldella
23. Burgessia
24. Leanchoilia
25. Sanctacaris
26. Ottoia
27. Louisella
28. Actaeus
29. Yohoia
30. Peronochaeta
31. Selkirkia
32. Ancalagon
33. Burgessochaeta
11. Micromitra
12. Echmatocrinus
13. Chancelloria
14. Pirania
15. Choia
16. Leptomitus
17. Dinomischus
18. Wiwaxia
19. Naraoia
20. Hyolithes
21. Habelia
1. Vauxia (gracile)
2. Branchiocaris
3. Opabinia
4. Amiskwia
5. Vauxia (robust)
6. Molaria
7. Aysheaia
8. Sarotrocercus

9. Nectocaris
10. Pikaia
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they may represent a full range of di-
ploblastic (two-layered) organization, of
which the modern phylum Cnidaria
(corals, jellyfishes and their allies) remains
as a small and much altered remnant.
In any case, they apparently died out
well before the Cambrian biota evolved.
The Cambrian then began with an as-
semblage of bits and pieces, frustrating-

ly difficult to interpret, called the “small
shelly fauna.” The subsequent main
pulse, starting about 530 million years
ago, constitutes the famous Cambrian ex-
plosion, during which all but one modern
phylum of animal life made a first ap-
pearance in the fossil record. (Geologists
had previously allowed up to 40 million
years for this event, but an elegant study,
published in 1993, clearly restricts this pe-
riod of phyletic flowering to a mere five
million years.) The Bryozoa, a group of
sessile and colonial marine organisms, do
not arise until the beginning of the sub-
sequent, Ordovician period, but this ap-
parent delay may be an artifact of failure
to discover Cambrian representatives.
Although interesting and portentous
events have occurred since, from the flow-
ering of dinosaurs to the origin of human
consciousness, we do not exaggerate
greatly in stating that the subsequent his-
tory of animal life amounts to little more
than variations on anatomical themes es-
tablished during the Cambrian explosion
within five million years. Three billion
years of unicellularity, followed by five
million years of intense creativity and then
capped by more than 500 million years
of variation on set anatomical themes
can scarcely be read as a predictable, in-
exorable or continuous trend toward
progress or increasing complexity.

We do not know why the Cambrian
explosion could establish all major ana-
tomical designs so quickly. An “external”
explanation based on ecology seems at-
tractive: the Cambrian explosion repre-
sents an initial filling of the “ecological
barrel” of niches for multicellular organ-
isms, and any experiment found a space.
The barrel has never emptied since; even
the great mass extinctions left a few spe-
cies in each principal role, and their oc-
cupation of ecological space forecloses
opportunity for fundamental novelties.
But an “internal” explanation based on
genetics and development also seems nec-
essary as a complement: the earliest mul-
ticellular animals may have maintained a
flexibility for genetic change and embry-
ological transformation that became
greatly reduced as organisms “locked in”
to a set of stable and successful designs.
Either way, this initial period of both
internal and external flexibility yielded a
range of invertebrate anatomies that may
have exceeded (in just a few million years
of production) the full scope of animal
form in all the earth’s environments to-
day (after more than 500 million years of
additional time for further expansion).
Scientists are divided on this question.
Some claim that the anatomical range of
this initial explosion exceeded that of
modern life, as many early experiments
died out and no new phyla have ever
arisen. But scientists most strongly op-

posed to this view allow that Cambrian
diversity at least equaled the modern
range—so even the most cautious opin-
ion holds that 500 million subsequent
years of opportunity have not expanded
the Cambrian range, achieved in just five
million years. The Cambrian explosion
was the most remarkable and puzzling
event in the history of life.
Dumb Luck
M O R E O V E R , W E D O N O T know why
most of the early experiments died, while
a few survived to become our modern
phyla. It is tempting to say that the vic-
tors won by virtue of greater anatomical
complexity, better ecological fit or some
other predictable feature of convention-
al Darwinian struggle. But no recognized
traits unite the victors, and the radical al-
ternative must be entertained that each
early experiment received little more
than the equivalent of a ticket in the
largest lottery ever played out on our
planet—and that each surviving lineage,
including our own phylum of verte-
brates, inhabits the earth today more by
the luck of the draw than by any pre-
dictable struggle for existence. The his-
tory of multicellular animal life may be
more a story of great reduction in initial
possibilities, with stabilization of lucky
survivors, than a conventional tale of
steady ecological expansion and mor-
phological progress in complexity.

Finally, this pattern of long stasis,
with change concentrated in rapid epi-
sodes that establish new equilibria, may
be quite general at several scales of time
and magnitude, forming a kind of fractal
pattern in self-similarity. According to
the punctuated equilibrium model of spe-
ciation, trends within lineages occur by
accumulated episodes of geologically in-
stantaneous speciation, rather than by
gradual change within continuous pop-
ulations (like climbing a staircase rather
than rolling a ball up an inclined plane).
Even if evolutionary theory implied a
potential internal direction for life’s path-
way (although previous facts and argu-
GREAT DIVERSITY quickly evolved at the dawn of
multicellular animal life during the Cambrian
period (530 million years ago). The creatures
shown here are all found in the Middle Cambrian
Burgess Shale fauna of Canada. They include
some familiar forms (sponges, brachiopods)
that have survived. But many creatures (such
as the giant Anomalocaris, at the lower right,
largest of all the Cambrian animals) did not live
for long and were so anatomically peculiar
(relative to survivors) that we cannot classify
them among known phyla.
41
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S C I E N T I F I C A M E R I C A N 97
ments in this article cast doubt on such
a claim), the occasional imposition of a
rapid and substantial, perhaps even tru-
ly catastrophic, change in environment
would have intervened to stymie the pat-
tern. These environmental changes trigger
mass extinction of a high percentage of
the earth’s species and may so derail any
internal direction and so reset the path-
way that the net pattern of life’s history
looks more capricious and concentrated
in episodes than steady and directional.
Mass extinctions have been recog-
nized since the dawn of paleontology; the
major divisions of the geologic time scale
were established at boundaries marked
by such events. But until the revival of in-
terest that began in the late 1970s, most
paleontologists treated mass extinctions
only as intensifications of ordinary
events, leading (at most) to a speeding up
of tendencies that pervaded normal
times. In this gradualistic theory of mass
extinction, these events really took a few
million years to unfold …

Gould, Stephen Jay, Natural History, 00280712, Sep90, Vol. 99,
Issue 9
The Golden Rule – A Proper Scale for Our Environmental Crisis
One among millions of species, we have a parochial, but
legitimate, interest in our own
survival. It takes a particular kind of genius or deep
understanding to transcend this most
pervasive of all conceptual biases and to capture a phenomenon
by grasping a proper
scale beyond the measuring rods of our own world. Phenomena
unfold on their own
appropriate scales of space and time and may be invisible in our
myopic world of
dimensions assessed by comparison with human height and
times metered by human life
spans. So much of accumulating importance at earthly scales—
the results of geological
erosion, evolutionary changes in lineages—is invisible by the
measuring rod of a human
life. So much that matters to particles in the microscopic world
of molecules—like the

history of a dust grain subject to Brownian motion—either
averages out to stability at our
scale or simply stands below our limits of perception.
The case at hand is a classic representative of a genre
(environmentalists versus
developers) made familiar in recent struggles to save
endangered populations—the snail
darter of a few years back, or the northern spotted owl versus
timber interests (decided,
properly in my view, for the birds).
The University of Arizona, with the backing of an international
consortium of
astronomers, wishes to build a complex of telescopes atop
Mount Graham in southeastern
Arizona. But the old-growth spruce-fir habitat on the
mountaintop forms the heart of the
range for Tamiasciurus hudsonicus grahamensis, the Mount
Graham red squirrel—a
distinct subspecies that lives nowhere else and that forms the
southernmost population of
the entire species. The population has already been reduced to
some 100 survivors, and

destruction of several acres of spruce-fir growth (to build the
telescopes) within the 700
or so remaining acres of best habitat might well administer a
coup de grace to this fragile
population.
I cannot state an expert opinion on details of this controversy.
Many questions
need to be answered. Is the squirrel population already too
small to survive in any case?
If not, could the population, with proper management, coexist
with the telescopes in the
remaining habitat? (Environmentalists fear change of
microclimate as much or more than
loss of acreage. Reduction of forest canopy will increase wind
and sun, producing a drop
in humidity. The squirrels survive winter by storing unopened
cones in food caches
beside trees. If humidity falls, cones may dry out and open,
causing loss of seeds and
destruction of food.)
I do not think that, practically or morally, we can defend a
policy of saving every
distinct local population of organisms. I can cite a good
rationale for the preservation of

species—for each species is a unique and separate natural object
that, once lost, can never
be reconstituted. But subspecies are distinct local populations
of species with broader
geographical ranges. Subspecies are dynamic, interbreedable,
and constantly changing;
what then are we saving by declaring them all inviolate? Thus, I
confess that I do not
agree with all arguments advanced by defenders of the Mount
Graham red squirrel. One
leaflet, for example, argues: "The population has been recently
shown to have a fixed,
homozygous allele which is unique in Western North America."
Sorry folks. I will stoutly
defend species, but we cannot ask for the preservation of every
distinctive gene, unless
we find a way to abolish death itself (for many organisms carry
unique mutations).
No, I think that for local populations of species with broader
ranges, the brief for
preservation must be made on a case-by-case basis, not a
general principle of

preservation (lest the environmental movement ultimately lose
popular support for trying
to freeze a dynamic evolutionary world in status quo). On this
proper basis of individual
merit, I am entirely persuaded that the Mount Graham red
squirrel should be protected
and the astronomical observatory built elsewhere—and for two
reasons. First, the squirrel
itself: the Mount Graham red is an unusually interesting local
population within an
important species. It is isolated from all other populations and
forms the southernmost
extreme of the species' range. Such peripheral populations,
living in marginal habitats,
are of special interest to students of evolution.
Second, the habitat: environmentalists continually face the
political reality that
support and funding can be won for soft, cuddly, and
"attractive" animals, but not for
slimy, grubby, and ugly creatures (of potentially greater
evolutionary interest and
practical significance) or for habitats. This situation has led to
the practical concept of
"umbrella" or "indicator" species—surrogates for a larger

ecological entity worthy of
preservation. Thus, the giant panda (really quite a boring and
ornery creature despite its
good looks) raises money to save the remaining bamboo forests
of China (and a plethora
of other endangered creatures with no political clout); the
northern spotted owl has just
rescued some magnificent stands of old-growth giant cedars,
Douglas fir, and redwoods;
and the Mount Graham red squirrel may save a rare and
precious habitat of extraordinary
evolutionary interest.
The Pinaleno Mountains, reaching 10,720 feet at Mount
Graham, are an isolated
fault-block range separated from others by alluvial and desert
valleys that dip to less than
3,000 feet in elevation. The high peaks of the Pinalenos contain
an important and unusual
fauna for two reasons. First, they harbor a junction of two
biogeographic provinces: the
Nearctic, or northern, by way of the Colorado Plateau, and the
Neotropical, or southern,
via the Mexican Plateau. The Mount Graham red squirrel (a
northern species) can live

this far south because high elevations reproduce the climate and
habitat found near sea
level in the more congenial north. Second, and more important
to evolutionists, the old-
growth spruce-fir habitats on the high peaks of the Pinalenos
are isolated "sky islands"—
10,000-year-old remnants of a habitat more widely spread over
the region during the
height of the last Ice Age. In evolutionary terms, these isolated
pieces of habitat are true
islands—patches of more northern microclimate surrounded by
southern desert. They are
functionally equivalent to bits of land in the ocean. Consider
the role that islands (like the
Galapagos) have played both in developing the concepts of
evolutionary theory and in
acting as cradles of origin (through isolation) or vestiges of
preservation for biological
novelties.
Thus, whether or not the telescopes will drive the Mount
Graham red squirrel to
extinction (an unsettled question well outside my area of
expertise), the sky islands of the

Pinalenos are precious habitats that should not be compromised.
Let the Mount Graham
red squirrel, so worthy of preservation in its own right, also
serve as an indicator species
for the unique and fragile habitat that it occupies.
But why should I, a confirmed eastern urbanite, choose to
involve myself in the
case of the Mount Graham red squirrel? The answer,
unsurprisingly, is that I have been
enlisted—involuntarily, unawares, and on the wrong side to
boot. I am simply fighting
mad, and fighting back.
The June 7, 1990, Wall Street Journal ran a pro-development,
anti-squirrel
opinion piece by Michael D. Copeland (identified as "executive
director of the Political
Economy Research Center in Bozeman, Montana") under the
patently absurd title: "No
Red Squirrels? Mother Nature May Be Better Off." (I can at
least grasp, while still
rejecting, the claim that nature would be no worse off if the

squirrels died, but I am
utterly befuddled at how anyone could argue that the squirrels
inflict a positive harm
upon the mother of us all!) In any case, Copeland
misunderstood my writings in
formulating a supposedly scientific argument for his position.
Now, scarcely a day goes by when I do not read a
misrepresentation of my views
(usually by creationists, racists, or football fans, in order of
frequency). My response to
nearly all misquotation is the effective retort of preference:
utter silence. (Honorable
intellectual disagreement should always be addressed;
misquotation should be ignored,
when possible and politically practical.) I make an exception in
this case because
Copeland cited me in the service of a classic false argument—
indeed, the standard,
almost canonical misuse of my profession of paleontology in
debates about extinction.
Paleontologists have been enlisted again and again, in
opposition to our actual opinions
and in support of attitudes that most of us regard as anathema,
to uphold arguments by

developers about the irrelevance (or even, in this case, the
benevolence) of modern
anthropogenic extinction. This standard error is a classic
example of failure to understand
the importance of scale—thus I return to the premise and
structure of my introductory
paragraphs.
Paleontologists do discuss the inevitability of extinction for all
species—in the
long run and on the broad scale of geological time. We are fond
of saying that 99 percent
or more of all species that ever lived are now extinct. (My
colleague Dave Raup often
opens talks on extinction with a zinging one-liner: "To a first
approximation, all species
are extinct.") We do therefore identify extinction as the normal
fate of species. We also
talk a lot—more of late since new data have made the field so
exciting—about the mass
extinctions that punctuate the history of life from time to time.
We do discuss the issue of
eventual "recovery" from these extinctions, in the sense that life
does rebuild or surpass

its former diversity after several million years. Finally, we do
allow that mass extinctions
break up stable faunas and, in this sense, permit or even foster
evolutionary innovations
well down the road (including the dominance of mammals and
the eventual origin of
humans, following the death of dinosaurs).
From this set of statements about extinction in the fullness of
geological time (on
scales of millions of years), some apologists for development
have argued that extinction
at any scale (even of local populations within years or decades)
poses no biological worry
but, on the contrary, must be viewed as a comfortable part of an
inevitable natural order.
Or so Copeland states:
Suppose we lost a species. How devastating would that be?
"Mass extinctions
have been recorded since the dawn of paleontology," writes
Harvard paleontologist
Stephen Gould ... the most severe of these occurred
approximately 250 million years ago
... with an estimated 96 percent extinction of species, says Mr.

Gould. ... There is general
agreement among scientists that today's species represent a
small proportion of all those
that have ever existed—probably less than 1 percent. This
means that more than 99
percent of all species ever living have become extinct.
From these facts, largely irrelevant to red squirrels on Mount
Graham, Copeland
makes inferences about the benevolence of extinction in general
(although the argument
applies only to geological scales):
Yet, in spite of these extinctions, both Mr. Gould and
University of Chicago
paleontologist Jack Sepkoski say that the actual number of
living species has probably
increased over time. [True, but not as a result of mass
extinctions, despite Copeland's
next sentence.] The "niches" created by extinctions provide an
opportunity for a vigorous
development of new species.... Thus, evolutionary history
appears to have been

characterized by millions of species extinctions and subsequent
increases in species
numbers. Indeed, by attempting to preserve species living on the
brink of extinction, we
may be wasting time, effort and money on animals that will
disappear over time,
regardless of our efforts.
But all will "disappear over time, regardless of our efforts"—
millions of years
from now for most species if we don't interfere. The mean life
span of marine
invertebrate species lies between 5 and 10 million years;
terrestrial vertebrate species turn
over more rapidly, but still average in the millions. By contrast,
Homo sapiens may be
only 250,000 years old or so and may enjoy a considerable
future if we don't self-
destruct. Similarly, recovery from mass extinction takes its
natural measure in millions of
years—as much as 10 million or more for fully rekindled
diversity after major
catastrophic events.

These are the natural time scales of evolution and geology on
our planet. But what
can such vastness possibly mean for our legitimately parochial
interest in ourselves, our
ethnic groups, our nations, our cultural traditions, our
bloodlines? Of what conceivable
significance to us is the prospect of recovery from mass
extinction 10 million years down
the road if our entire species, not to mention our personal
family lineage, has so little
prospect of surviving that long?
Capacity for recovery at geological scales has no bearing
whatever upon the
meaning of extinction today. We are not protecting Mount
Graham red squirrels because
we fear for global stability in a distant future not likely to
include us. We are trying to
preserve populations and environments because the comfort and
decency of our present
lives, and those of fellow species that share our planet, depend
upon such stability. Mass
extinctions may not threaten distant futures, but they are
decidedly unpleasant for species
in the throes of their power (particularly if triggered by such

truly catastrophic events as
extraterrestrial impact). At the appropriate scale of our lives,
we are just a species in the
midst of such a moment. And to say that we should let the
squirrels go (at our immediate
scale) because all species eventually die (at geological scales)
makes about as much sense
as arguing that we shouldn't treat an easily curable childhood
infection because all
humans are ultimately and inevitably mortal. I love geological
time—a wondrous and
expansive notion that sets the foundation of my chosen
profession, but such immensity is
not the proper scale of my personal life.
The same issue of scale underlies the main contributions that
my profession of
paleontology might make to our larger search for an
environmental ethic. This decade, a
prelude to the millennium, is widely and correctly viewed as a
turning point that will lead
either to environmental perdition or stabilization. We have
fouled local nests before and

driven regional faunas to extinction, but we have never been
able to unleash planetary
effects before our current concern with ozone holes and putative
global warming. In this
context, we are searching for proper themes and language to
express our environmental
worries.
I don't know that paleontology has a great deal to offer, but I
would advance one
geological insight to combat a well-meaning, but seriously
flawed (and all too common),
position and to focus attention on the right issue at the proper
scale. Two linked
arguments are often promoted as a basis for an environmental
ethic:
1. That we live on a fragile planet now subject to permanent
derailment and
disruption by human intervention;
2. That humans must learn to act as stewards for this threatened
world.
Such views, however well intentioned, are rooted in the old sin
of pride and
exaggerated self-importance. We are one among millions of

species, stewards of nothing.
By what argument could we, arising just a geological
microsecond ago, become
responsible for the affairs of a world 4.5 billion years old,
teeming with life that has been
evolving and diversifying for at least three-quarters of that
immense span? Nature does
not exist for us, had no idea we were coming, and doesn't give a
damn about us.
This assertion of ultimate impotence could be countered if we,
despite our late
arrival, now held power over the planet's future (argument
number one above). But we
don't, despite popular misperception of our might. We are
virtually powerless over the
earth at our planet's own geological time scale. All the
megatonnage in our nuclear
arsenals yield but one ten-thousandth the power of the asteroid
that might have triggered
the Cretaceous mass extinction. Yet the earth survived that
larger shock and, in wiping
out dinosaurs, paved the road for the evolution of large
mammals, including humans. We
fear global warming, yet even the most radical model yields an

earth far cooler than many
happy and prosperous times of a prehuman past. We can surely
destroy ourselves, and
take many other species with us, but we can barely dent
bacterial diversity and will surely
not remove many million species of insects and mites. On
geological scales, our planet
will take good care of itself and let time clear the impact of any
human malfeasance.
People who do not appreciate the fundamental principle of
appropriate scales
often misread such an argument as a claim that we may
therefore cease to worry about
environmental deterioration—just as Copeland argued falsely
that we need not fret about
extinction. But I raise the same counterargument. We cannot
threaten at geological
scales, but such vastness is entirely inappropriate. We have a
legitimately parochial
interest in our own lives, the happiness and prosperity of our
children, the suffering of
our fellows. The planet will recover from nuclear holocaust, but
we will be killed and
maimed by the billions, and our cultures will perish. The earth

will prosper if polar
icecaps melt under a global greenhouse, but most of our major
cities, built at sea level as
ports and harbors, will founder, and changing agricultural
patterns will uproot our
populations.
We must squarely face an unpleasant historical fact. The
conservation movement
was born, in large part, as an elitist attempt by wealthy social
leaders to preserve
wilderness as a domain for patrician leisure and contemplation
(against the image, so to
speak, of poor immigrants traipsing in hordes through the woods
with their Sunday picnic
baskets). We have never entirely shaken this legacy of
environmentalism as something
opposed to immediate human needs, particularly of the
impoverished and unfortunate.
But the Third World expands and contains most of the pristine
habitat that we yearn to
preserve. Environmental movements cannot prevail until they
convince people that clean

air and water, solar power, recycling, and reforestation are best
solutions (as they are) for
human needs at human scales—and not for impossibly distant
planetary futures.
I have a decidedly unradical suggestion to make about an
appropriate
environmental ethic—one rooted, with this entire essay, in the
issue of appropriate human
scale versus the majesty, but irrelevance, of geological time. I
have never been much
attracted to the Kantian categorical imperative in searching for
an ethic—to moral laws
that are absolute and unconditional and do not involve any
ulterior motive or end. The
world is too complex and sloppy for such uncompromising
attitudes (and God help us if
we embrace the wrong principle, and then fight wars, kill, and
maim in our absolute
certainty). I prefer the messier "hypothetical imperatives" that
invoke desire, negotiation,
and reciprocity. Of these "lesser," but altogether wiser and
deeper, principles, one has
stood out for its independent derivation, with different words
but to the same effect, in

culture after culture. I imagine that our various societies grope
toward this principle
because structural stability, and basic decency necessary for any
tolerable life, demand
such a maxim. Christians call this principle the "golden rule";
Plato, Hillel, and
Confucius knew the same maxim by other names. I cannot think
of a better principle
based on enlightened self-interest. If we all treated others as we
wish to be treated
ourselves, then decency and stability would have to prevail.
I suggest that we execute such a pact with our planet. She holds
all the cards and
has immense power over us—so such a compact, which we
desperately need but she does
not at her own time scale, would be a blessing for us, and an
indulgence for her. We had
better sign the papers while she is still willing to make a deal. If
we treat her nicely, she
will keep us going for a while. If we scratch her, she will bleed,
kick us out, bandage up,
and go about her business at her planetary scale. Poor Richard
told us that "necessity
never made a good bargain," but the earth is kinder than human

agents in the "art of the
deal." She will uphold her end; we must now go and do
likewise.

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