TREE vol. 7, no. 7, July 1992
However, Raup himself contradicts
the first claim, as the end-Permian
event is simply too great to be
considered as part of this continuum.
Also, several studies have shown that
the selectivity of extinctions during
mass extinction intervals appears
to be different from that operating
during background times. Regarding
claim (21, the evidence for meteorite
impact at the end of the Cretaceous
is good, although it may have little
to do with the actual extinctions.
There is simply no evidence at all
for meteorite impacts at times of rent extinction theory, for its elegant
other major mass extinction events. use of statistics, and for its carefully
Finally, the biggest impact craters did constructed arguments for an idea -
not form at moments of mass ex- that all mass extinctions are caused
tinction. For example the 70 km by meteorite impact - that is surely
diameter Manicouagan Crater near wrong.
Quebec used to be implicated in the
Triassic/Jurassic boundary mass ex- Paul B. Wignall
tinction but the crater has now been
more accurately dated as Late TriasDept
of Earth Sciences, University of Leeds, Leeds,
sic - over 20 million years older.
UK LS2 9JT
Despite its astounding main con- Reference
elusion, this is a book worth read- 1 Raup, D.M. (1979) Science 206,
ing for its succinct summary of cur- 217-218
. . . and more Extinction
The Miner’s Canary: Unraveling the Mysteries
of Extinction
by Niles Eldredge, Prentice Hall, 7997.
$79.50 (246 paged ISBN 0 73 583659 X
On Methuselah’s Trail: Living Fossils and the
Great Extinctions
by Peter Douglas Ward, W.H.
Freeman & Co., 7992. $78.95 (212
pages) ISBN 0 7767 2203 8
Some paleontologists are in a quandary
of late. They have been successful
(apparently) in documenting
episodes of substantial extinction,
and they have suggested and tested
hypotheses of cause for at least some
of these episodes. At the same time,
neontologists have been growing
increasingly concerned over extinction
today, to the point where it is
now commonplace to hear comparisons
between what happened to
the dinosaurs and what is happening
now in tropical rain forests.
The quandary lies here: in the
midst of what all informed sources
see as nothing short of a crisis in the
history of life, what should be the
response of a profession that claims
to know more than any other about
that history? Should we hope for
some of the scraps of ‘biodiversity’
funding to trickle down to research on
ancient biodiversity, whether or not
it is relevant to the Recent? Should
we abandon fossils and devote ourselves
to making inventories of the
Recent representatives of our respective
groups? (Paleontologists, it
turns out, are often the only systematists
working on many living
groups.)
In the mid-1980s a few paleontologists
began to see that perhaps
they did have something to offer to
neontologists. If extinction is so common
in Earth history, maybe paleontology
can indicate either (I) something
general about its cause, or (2)
something general about its effect1z2.
But paleontology has been much
more successful in the latter than the
former. Many workers now would
agree that mass extinction is ‘more
frequent, more rapid, more extensive
in impact and more qualitatively
different in effect’ than previously
believed3, and that, at least in some
cases, it alters the long-term patterns
of evolutionary history. Even if it does
not, as Gould has suggested, operate
as an autonomous ‘third tier’ of
process3, by the very magnitude and
rapidity that define it, it acts as an
incredibly strong dose of historical
contingency, which alters the
shape and subsequent biosphere.
The world after mass extinction isn’t
just the world minus what disappeared;
it is often a qualitatively
different place4.
So to the barricades we go, armed
withtheinformationthatthesituation
is even worse than we thought. If we
causethe equivalent of a mass extinction
in the next few centuries, we will
not only bequeath to our descendants
an impoverished world, we will
havealteredfundamentallytheshape
of things to come. What a satisfying
response to the anthropocentric
rantings of those who say that both
humans and extinction are parts of
nature and the outcome can therefore
be nothing but natura15.
But is this all we can do? With more
than a score of ‘mass extinctions’ to
choose from, can we not say anything
socially - or at least neontologically
- useful about the causes of extinction?
Niles Eldredge has written a
popular book of the sort that many
paleontologists would probably like
to have written. It is a book that
other paleontologists should read to
become inspired, and that neontologists
should read to get some
feeling for what kinds of questions
they can reasonably expect paleontologists
to answer for them.
The book is actually something of
a hybrid. It is half a personal response
to the impending crisis, and half an
outgrowth of Eldredge’s technical
work over the last decade. Readers
familiarwith his previous books6,7wiII
see in this one a logical extension of
Eldredge’s ideas about what factors
govern the origin of species. And he
is quite unambiguous about the
result: ‘I set out to write this book with
the goal . . . of finding a simple,
overarching theory of extinction’ he
writes in the Prologue. And he concludes,
‘I am convinced I have found
it. . . . It sees ecosystem collapse and
the extinction of species as the
outcome, generally, of earthbound
causes. These causes are simply the
flip side of the same factors that build
and maintain ecosystems and lead to
the evolution of species in the first
place.’
Eldredge’s basic conclusion is that
‘change of size and location of habitat
underlies most extinction events,
ranging from isolated species disappearances
through the most massive
of extinctions’. And he concludes that
‘Global climate change, especially
global cooling, seems to have been
the prime cause of habitat disruption.’
One can quibble about the
details, for example Eldredge’s statement
of an emerging ‘consensus’
about the effects of global cooling at
mass extinction, without disagreeing
with the importance of ecosystem
collapse.
Yet despite the power of Eldredge’s
conclusion, a reader might still be left
asking: so that’s all there is? All
that paleontology has to contribute
to solving this crisis is to note that
ecosystem collapse is bad, pass this
information along toconservationists
and go back to studying fossils?
The argument forthe importance of
preserving whole ecosystems (and,
by inference, the role of catastrophic
ecosystem collapse and random killing
during mass extinction) is surely
strengthened if what Eldredge says is
245
TREE vol. 7, no. 7, July 7992
true. But it may not be the entire
story. We are still woefully ignorant
of the ecology across mass extinction
boundaries, of the anatomy (and thus
the causes) of ecosystem collapse
going in and of recovery coming out.
We do not really know why particular
taxa go extinct - in other words, the
causal basis for what we already said
we did know, that mass extinction
sorts out who will be the progenitors
of the future. Ecology may matter or
it may not.
What we need to find out is more
natural history of the taxa, communities
and ecosystems that do and
do not become extinct. Although it is
not apparent for a number of pages,
it is here that Peter Ward’s book on
living fossils is relevant to the issue
of mass extinction. He discusses
eight or so groups that seem to show
extraordinary evolutionary longevity,
and concludes in a telling statement
that ‘The great trick in the history of
life apparently lies in being able to
survive a mass extinction’. The book
is about why these ‘Methuselahs’,
and not other taxa, have survived the
‘great extinctions’. Ward’s answer
appears to be mixed. He repeatedly
emphasizes resistance to predation
(or resistance to marginal habitats
away from predation), for example,
as a recurrent theme in the survival
of living fossils. Toward the end,
however, Ward concludes that ‘One
word sums up the reason for many of
these survivals: luck’.
What then is a concerned paleontologist
to say? And should neontologists
listen?
The convergence of intellectual
currents that marked the beginning of
the extinction craze more than
a decade ago may continue as
paleontologists now concentrate on
the details of what actually happens
across mass extinction boundaries,
and conservation biologists
learn more about which individual
species will disappear from ‘disturbed’
ecosystems first. We already
knew that preserving functioning
habitat was better than preserving
species. But trade-offs seem to be
inevitable; we will not be able to
preserve everything. In such a
situation, it may make an important
difference whether or not individual
natural history ‘matters’. If choices
are to be made, the long time scale
available to paleontologists may
provide an additional perspective on
the consequences of letting some
species or habitats disappear, while
fighting to save others.
Warren D. Allmon
Dept of Geology, University of South Florida, Tampa,
FL 33620, USA
References
1 Stanley, S. (1985) in Animal
Extinctions: What Everyone Should
Know (Hoage, R.J., ed.), pp. 31-46,
Smithsonian Institution Press
2 Jablonski, D. (1986) in The Last
Extinction (Kaufman, L. and Mallory, K.,
eds), pp. 43-62, MIT Press
3 Gould, S.J. (1985) faleobiology 11,
2-l 2
4 Jablonski, D. (1986) Science 231,
129-133
5 Palmer, T. (1992) The Atlantic Monthly
January, 83-88
6 Eldredge, N. (1985) Unfinished
Synthesis: Biological Hierarchies and
Modern Evolutionary Thought, Oxford
University Press
7 Eldredge, N. (1989) Macroevolutionary
Dynamics: Species, Niches and
Adaptive Peaks, McGraw-Hill
Acidification
Acidic Deposition: Its Nature and Impacts
edited by F.T. Last and R. Watling, The
Royal Society of Edinburgh, 7997.
f42.00/$84.00 pbk (xxiv + 344 pages)
ISBN 0 902798 07 6
Acidification Research in the Netherlands:
Final Report of the Dutch Priority Programme
on Acidification
edited by G.J. Heij and T. Schneider,
Elsevier (Studies in Environmental
Science Vol. 46), 7997. $725.50/
Dfl. 420.00 (xii + 772 pages) ISBN
0444888374
246
Together the books show how the
emphasis of research on acidification
These two volumes provide respectively
an international and a
national (Dutch) perspectiveof recent
research on acidic deposition and its
impacts. Acidic Deposition comprises
the keynote papers, plus a
critique, from the most recent of a
series of international conferences
held at six-yearly intervals; this latest
conference was held in Glasgow in
1990. Acidification Research in the
Netherlands is built around the final
report of the second phase of the
Dutch national priority research
programme.
has changed over the last 20 years
and how the sources of emissions
and causes of acidification can vary
between countries. Nitrogen now
receives much greater attention than
in the past and dominates the Dutch
research programme. As industrial
emissions of sulfur have declined in
northwest Europe, vehicular emissions
have increased and agricultural
emissions of nitrogen dominate in
the Netherlands. Early work focused
on the extent of damage while
current research centres on damage
mechanisms and on recovery.
Emission control was formerly the
province of engineers and politicians
but environmental scientists now
have a central role in determining
critical loads.
The papers in Acidic Deposition
cover elements of most of the main
Both volumes also illustrate how
progress in our understanding of
acidic deposition and its impacts
has been built on a combination
of field observation and measurement,
manipulative experiments and
modelling. The balance between research
approaches has changed over
the last 20 years with increasing
emphasis on manipulative experiments
and modelling as opposed to
field observation.
aspects of research on this topic, from
atmospheric oxidation processes and
deposition mechanisms to impacts
on forests, surface waters and building
materials. But the reader hoping
for a comprehensive review of the
current state of knowledge across
the whole field of acidic deposition
research will be disappointed. There
is no overview of recent work on
crops or emissions and the paper on
atmospheric chemistry is a detailed
consideration of one aspect, the role
of the hydroxyl radical in oxidation
processes. However, there are good
overviews of current understanding
of the causes of forest dieback,
deposition processes, the causes of
recent acidification of forest soils, and
impacts on aquatic biota. Most of the
papers fall short of being the type of
keynote paperthat research scientists
will refer to frequently but some
are undoubtedly of this quality,
notably the review of studies involving
experimental acidification of lake
ecosystems in central North America
and the overview of research on
forest dieback.
The critique provides a useful,
if rather lengthy, survey across
the whole topic for the general
reader, research manager and decision
maker. The summary to the