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Niles Eldredge:
Paleontology and Evolutionary Theory
By Ebbe Sloth Andersen
Niles Eldredge is
a paleontologist who for more than 30 years has worked at the prestigious
American Museum of Natural History in New York. Back in the days when
Eldredge joined the Museum, paleontology must have been a somewhat dusty
discipline that served to classify fossils and to provide evidence for
evolutionary biology. But in the early 1970s Eldredge and his colleague
Stephen Jay Gould (who died in May 2002) contributed to give paleontology
a much more important role. To be more specific, it may be argued that
their common work marks the moment of the change of paleontology from
a passive role of interpreting the fossil data in the light of evolutionary
theory to an active role in the further refinement of this theory.
Missing links The path-breaking
contribution by Eldredge and Gould was to explain that the much-discussed
"missing links" in the fossil record is partly due to the process of
evolution itself. They made the hypothesis that a new species gets its
major characteristics so quickly that it is unlikely that we shall ever
find a fine-graded series of fossil specimens that demonstrates the
transformation from its ancestor. On the other hand, when the species
has got its major characteristics, it will normally show practically
no further evolution (stasis).
Facts and theories The Eldredge-Gould
hypothesis raised two questions. The first is whether the fossil record
actually shows a pattern of punctuations that disrupt long periods of
evolutionary stasis. To answer this question paleontologists have had
to collect new fossils and, even more important, to develop precise
empirical methods. These efforts have themselves improved the level
of scientific work in the area. The answer to the question has been
more mixed, but although the debate has not ended it is fair to say
that the Eldredge-Gould hypothesis explains quite many, but by far all,
of the results. The second question
is whether their hypothesis calls for a revision of standard evolutionary
theory. This question has been emphasised in much subsequent work by
Eldredge and Gould (both collectively and individually). For both the
answer is a clear yes. For them the standard neo-Darwinian evolutionary
theory seem to have hardened into an "ultra-Darwinism" that overemphasises
gene-level natural selection (like Richard Dawkins's Selfish Gene).
Instead they think that evolutionary theory should include explicitly
a whole hierarchy of selection-relevant entities from organisms to species
and higher taxonomic levels; it should also include a hierarchy of
ecological niches. It is within these complex systems and multiple levels
of selection that they suggest that evolution occurs by punctuated equilibrium.
It is only within such a complicated framework that Eldredge and Gould
think that the surprising patterns in the evolutionary history becomes
fully explainable. The Great Controversy The call for a revision
of neo-Darwinism has created a good deal of controversy, which has also
been remarked by the public. Parts of the controversy seem to have its
background in misunderstandings due to different modes of thinking.
The paleontologists have not been able to put their arguments in genetic
terms and the evolutionary theorists could not easily interpret sketchy
ideas like punctuated equilibrium. At the end some degree of mutual
understanding has, however, emerged. It is e.g. obvious that gradual
natural selection allows changes that are very quick on a paleontological
time scale. Thus it is obvious that the Eldredge-Gould patterns are
compatible with natural selection. In this and other
ways the rebellious paleontologists have joined the "High Table" of
evolutionary theorising (to use an expression by Eldredge), and they
seem to have been given a rather fair treatment in the major textbooks
on evolutionary biology (e.g. Futuyma, Ridley). It is, however, still
discussed whether the pattern of punctuated equilibrium has now been
largely accounted for by neo-Darwinian theory (the viewpoint of Dawkins,
Maynard Smith and Wilson) or whether there is still a lot that needs
to be done (the viewpoint of Eldredge). A good deal of Eldredge's work
has consisted in developing and promoting his view, but in the end the
answer has to be given with reference to empirical evidence. It is,
for instance, an empirical question whether a mature species is characterised
by a genome that is flexible to react to environmental pressures (the
neo-Darwinian viewpoint) or whether such a species is characterised
by interacting genes that prevents such reactions (and explains stasis). In the meantime the
task is to keep the theoretical debate open, both for its own sake and
in order to understand present-day issues like the crisis of biodiversity.
One strategy for upholding the debate is to enter into the history of
evolutionary ideas. This strategy is to some extent followed by Eldredge,
but the history of ideas was the speciality and favourite area for his
friend Gould, who before he died succeeded in finalising a huge volume
on the history and "Structure of Evolutionary Theory". Another strategy
is closer to the heart of Eldredge. It is to give accounts of the history
of the evolution of species (e.g. in "The Pattern of Evolution"). These accounts allows
Eldredge once more to explain his doubts about the standard evolutionary
theory of e.g. Dawkins. Thus he can provide evidence that morphological
evolution does not occur all the time and that species appear to be
quite stable and often last for millions of years. Their extinction
is due to environmental events that wipe out not only species but whole
ecosystems. Evolution is due to the survivors of extinction, which
radiate to fill the open niches. This is, of course, neo-Darwinian evolution,
but it does not have the gradualistic character, which Eldredge think
is taught by the "ultra-Darwinists". For empirically oriented European
researchers it is, however, still not clear how far Eldredge and Gould
go beyond the neo-Darwinists or even beyond Darwin. Monkey business The debate among evolutionary
theorists has received much attention from outsiders. Many philosophers
and social scientists have, for instance, been very interested in the
explanations of patterns of punctuated equilibrium, and Eldredge has
contributed to their debates. But there has also been interest from
a more troublesome side: religious fundamentalists. This group has been
especially active in the United States, where it has promoted "creation
science" and other kinds of would-be alternatives to the school-level
teaching of evolutionary theory. The practitioners of such "sciences"
have a strange method: they know the answer (God created all species
or at least humans) before they start to study the question (how have
species emerged?). For reasons that probably
belong to both politics and social psychology this nonsense is still
quite widespread, and Eldredge has had to spend quite much time in his
fight against it. Previously he published the book on "Monkey Business"
and recently he wrote "The Triumph of Evolution and the Failure of Creationism".
His special interest in this topic is probably due to the fact that
creationists in their never-ending search for new arguments have put
some emphasis on punctuated equilibrium. This is partly due to the search
for areas where "missing links" seem to persist (and thus to give room
for divine intervention), which started immediately after Darwin's "Origin
of Species". But the creationists also try to find scientific controversies
that demonstrate that evolution is "just a theory". Thus Eldredge not
only needs to explain the fossil record and the driving forces of evolution.
He also has to explain that disagreement is a way of promoting understanding
among real scientists and that basic evolutionary theory is one of the
most solid cornerstones of modern science. Where to go It is obvious that
Eldredge is a pioneer whose work has done much to promote paleontology,
evolutionary theory and the public understanding of science. Much will
probably follow, and one may ask about the direction of his work. There
are few signs that the molecular evidence will become more integrated
into the work of Eldredge. This is a pity, at least from the viewpoint
of a molecular biologist. The molecular evidence of evolution is an
extremely rich and daily expanding source to promote arguments against
creationists and for particular refinements of evolutionary theory.
Its relevance seems to be increasingly acknowledged in paleontology
and it may help to clarify many issues. But evolutionary ecology is
also an important area of research,
and Eldredge is moving in its direction. In this way he can both explore
his complicated framework and confront the issues of biodiversity and
extinctions. Some books by Niles
Eldredge:
Fossils, Princeton
University Press. Reinventing Darwin,
Wiley. The Pattern of Evolution,
Freeman. The Triumph of Evolution
and the Failure of Creationism, Freeman. Life in the Balance,
Princeton University Press. Unfinished
Synthesis, Oxford University Press.
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This
process of "punctuated equilibrium" seemed to show up in Eldredge's
study of the evolution of a new species of trilobites that took place
more than 350 million years ago, and his unique data seemed to be explainable
by the emergence of new species in small populations at the fringe of
old species (suggested by the grand evolutionist Ernest Mayr). Gould
put this idea into a clear and provoking form, and punctuated equilibrium
has been on the scientific agenda ever since.