“GENETICISTS and palaeontologists,” says Niles Eldredge, “are still very much
at each other’s throats” in discussions of evolution. Never one to leave a
geneticist’s throat unscarred, palaeontologist Eldredge is on the attack
again.

The difference of viewpoint that he prefers to sustain as a quarrel centres
on the theory of punctuated equilibria that he published, with Stephen Jay
Gould, in an influential paper in 1972. They argued that evolution does not
generally proceed by slow, continuous change, but as a series of relatively
rapid changes separated by long intervals in which nothing much happens. Their
antagonists, whom Eldredge describes sometimes as “geneticists” and sometimes as
“ultra-Darwinists”, do not disagree, but they do not regard punctuated
equilibrium as a seminal insight. Rather, they see it as an expected consequence
of conventional Darwinian theory that is predicted by mathematical modelling.
The division between Eldredge and Gould on the one hand, and the
ultra-Darwinists led by John Maynard Smith and Richard Dawkins on the other,
concerns approaches rather than conclusions.

Eldredge’s approach to science is clearly displayed in The Pattern of
Evolution. Its main theme is that “science is a search for resonance
between mind and natural pattern”, a theme that he presents by reviewing the
largely familiar histories of the study of evolution and of geology over the
past two centuries. The problem is that he uses the word “pattern” so broadly
that its meaning is scarcely discernible. Like Lewis Carroll’s Humpty Dumpty,
when Eldredge says “pattern” it means what he wants it to mean. Often he uses it
to refer to a recurrent event, such the appearance of pioneering species in
patches of forest devastated by storms. At other times it is applied to an
observation that can be made repeatedly on different material, such as the
similarity between embryos of distantly related species. In one instance he uses
it to describe a unique observation: the fit between the coastlines of Africa
and America that seems to be a consequence of their being parts of a
supercontinent that has broken up.

Eldredge argues that which patterns are chosen, and how they are presented,
is critical to the acceptance of novel science. He contrasts Alfred Wegener’s
failure in the 1920s to convince the scientific world that the continents had
separated and moved, with Stanley Runcorn’s success in the 1960s. He argues that
Wegener damaged his credibility by mixing good points with ambiguous evidence,
and by uncritically accepting erroneous measurements. Runcorn used much of the
same evidence, but by marshalling it better, avoiding errors and adding evidence
of palaeomagnetic measurements, managed to win immediate acceptance.

Eldredge also contrasts Lamarck’s failure with Darwin’s success. Lamarck
presented some sound evidence that evolution had occurred, together with a
mechanism for evolution that seemed thoroughly plausible. His ideas won little
acceptance, but Darwin’s superbly marshalled evidence rapidly won over the
scientific world.

While Eldredge’s recurring theme in The Pattern of Evolution is the
role in science of the perception of pattern, his main idea only becomes
apparent in the final chapter. Here he promotes an extension of the theory of
punctuated equilibria: physical events, he says, trigger short periods of
relatively rapid change. The uneventful life of a patch of forest is interrupted
from time to time by brief episodes of renewal following devastation by storms.
The amazing proliferation of species of cichlid fishes in Lake Victoria followed
a period when the lake dried up, destroying the previous fauna.

Eldredge sees the minor changes, on which earlier discussions of punctuated
equilibria focused, as part of this pattern. But he does little to establish the
role of physical events in causing the punctuation. In the sole example he
describes in any detail, he shows that in one area trilobites with 18 rows of
facets in their eyes were replaced by ones with only 17 rows when the sea
withdrew and then returned, giving the 17-rowers the opportunity to invade from
a neighbouring area where they were already established. What is missing is
evidence that physical events played a part in the initial evolution of the new
form.

Most biologists would probably agree that episodic evolution triggered by
physical events has played a major role in the history of life. Many would claim
to have believed it for some years, and the forceful presentation of this idea
in The Pattern of Evolution ought to be welcome. The book’s
weakness is that describing a few striking examples, no matter how eloquently,
does not establish that that these examples are the norm. To do that, Eldredge
would need to present a wide range of examples, involving different groups of
organisms at different times and in different places. A systematic review of all
available examples would probably show that episodic evolution following
physical events occurred in most of them. But Eldredge fails to provide such
review, and relies instead more on rhetoric than analysis.

Eldredge attaches great importance to the place in his theory of physical
events such as natural disasters. For some reason, he seems to feel that these
links between evolution and “matter-in-motion” give punctuated equilibrium
new respectability. He also highly values the concept of hierarchy, relating the
hierarchy of taxa that we use to classify organisms to an ecological hierarchy
consisting of organisms, avatars (by which he means a local population of
organisms of the same species), local ecosystems and regional ecosystems. This
link seems at best unhelpful.

“Science, at its best, should leave room for poetry,” Richard Dawkins wrote
in Unweaving the Rainbow
(Review, 21 November 1998, p 50). “It should
note helpful analogies and metaphors that stimulate the imagination, conjure in
the mind images and allusions that go beyond the needs of straightforward
understanding. But there’s bad poetry as well as good, and bad poetic science
can lead the imagination along false trails.” Dawkins accused Stephen Jay Gould
of bad poetry in his case for episodic evolution, claiming that he plays with
words to forge spurious links between phenomena as different as punctuated
equilibrium, evolution by large macromutational jumps, and the catastrophic
extinction of the dinosaurs. In The Pattern of Evolution,
Eldredge lays himself open to similar accusations of bad poetry by using the
words “pattern”, “hierarchy” and “episodic” to make potentially misleading links
between dissimilar ideas.

Eldredge’s book is well endowed with notes and a comprehensive bibliography,
and it should be thoroughly accessible to anyone with a basic knowledge of
Darwin’s and Lamarck’s theories. But if they come away with new insights into
the history of life, I fear that it will be through being seduced by poetry
rather than being convinced by scientific evidence.

AN ADULT ostrich is an overgrown, oversexed chicken. Its feathers are downy,
more like those of a chicken than of other adult birds. Like chickens, it has
strong legs but small, ineffective wings. Also, its skull bones remain unfused.
While retaining these juvenile characteristics, the ostrich becomes sexually
mature.

This phenomenon—known as paedomorphosis—is one aspect of
heterochrony, the subject of Kenneth McNamara’s Shapes of Time.
Heterochrony is an evolutionary change in the timing of development. Whereas
paedomorphosis involves retardation of development of the affected
characteristics, peramorphosis takes development beyond the ancestral state.

McNamara sees all evolutionary change as heterochrony. The tiny forelegs of
tyrannosaurs are a case of paedomorphosis and the formidable head is
peramorphosis. The downy feathers of the ostrich are seen as paedomorphosis and
the large body as peramorphosis. He writes about contrasting views of human
evolution, with some scientists seeing us as paedomorphic, baby-faced apes and
others as peramorphic super-apes. He feels that the “emperor’s new clothes”
effect is in evidence here. I am inclined to think that he himself is rather
good at imagining clothes on nude emperors. If every increase in the size or
complexity of an organ, in the course of evolution, is seen as peramorphosis and
every decrease as paedomorphosis, long words are being used where short ones
would do as well.

Early in the book, McNamara writes about hox genes and hormones, raising
hopes that he will show us how heterochrony is brought about. But he shows us a
link between mechanism and effect only in a few cases, without providing much
detail.

His book is pleasantly and clearly written, and assumes little prior
knowledge of biology. It has some splendid diagrams that make their points
brilliantly. However, there are fewer illustrations than I would expect to find
in a book about animal shapes. Readers not familiar with the animals and
structures may have difficulty picturing them.

This is Biology: The Science of the Living World by
Ernst Mayr, Belknap/Harvard University Press, ÂŁ19.95/$29.95,
ISBN 0 674 88468 X

Evolution and the Diversity of Life by Ernst Mayr,
ÂŁ16.50, ISBN 0 674 27105 X

HE IS acknowledged to be one of the great zoologists of the 20th century. His
contributions to evolutionary biology have been recognised by a dazzling
collection of the world’s most prestigious scientific awards—no Nobel
prize (none is available in his field) but almost every other prize that you can
think of. Now 92, Ernst Mayr has written a wide-ranging review of biological
thought and progress. In part, This is Biology is a study of the
philosophy of biology, and in part a history of selected branches of the
subject.

Mayr begins by asking what “life” means. He outlines 19th-century
controversies between physicalists and vitalists, and then lists the properties
that seem to him diagnostic of life.

Next, Mayr asks what science is and how it explains the world. He points out
that philosophers’ views of the nature of science have more often been
applicable to the physical sciences than to biology. He writes: “There is more
difference between physics and evolutionary biology—both of which are
branches of science—than between evolutionary biology (one of the
sciences) and history (one of the humanities).” I would like to have seen
engineering brought into this discussion. There are large areas of biology
(functional morphology and physiology as well as the obvious case of
biomechanics) that are in effect inverse engineering. Engineers design
structures and mechanisms to perform specified functions, while biologists in
these fields work out how living structures and mechanisms perform the functions
for which evolution has designed them.

Mayr discusses Karl Popper’s physics-based account of the scientific method:
scientists formulate hypotheses and then try to falsify them. Hypotheses can be
destroyed but can never be proved right. For biology, Mayr offers a five-stage
process. ĐÓ°ÉÔ­´´s make observations; they ask questions of “how?” or “why?”;
they formulate hypotheses; they test their hypotheses; and they adopt the most
successful hypothesis. This gives us more room to manoeuvre than Popper’s
account, but I doubt whether many of us work as systematically as that.

Journals tell us little about how scientists actually operate, because we
structure our papers to conform to the conventional format. But I’m sure my
research group is not exceptional in the roundabout routes we take in our
studies. As an example, consider our paper “Dynamic similarity hypothesis” (
Journal of Zoology, vol 201, p 135) which predicts how differences of size
between animals affect the relationship between speed and gait.

We had been working on mammal and bird running, calculating energy costs. For
that, I had devised simple mathematical models of walking and running. I was
then asked to speak at a conference on “Scale effects in animal locomotion”. I
was looking for something new to say when I noticed that the dimensionless
number u²/gh (speed squared/(gravitational acceleration × leg
length)) appeared repeatedly in my equations. That led me to guess that animals
of different sizes running with equal values of u²/gh might
move in similar ways (using the same gait, and taking strides proportional to
the lengths of their legs).

Tests of that idea (initially using data from Eadweard Muybridge’s classic
photographs) confirmed it. Only at that stage did I refer to a textbook of
dimensionless analysis and realised that u²/gh is a Froude
number, a quantity used to indicate the influence of gravity on fluid motion,
and that a well-established physical principle should have made me expect
similar gaits at equal Froude numbers. Mayr and other philosophers of science
would like us to progress in a more orderly way than that.

Much of the rest of Mayr’s book is devoted to discussion of the kinds of
questions that biologists ask, which he classifies as “what?”, “how?” and “why?”
questions. “What?” questions establish the descriptive base, the first stage of
Mayr’s five-stage process for biology. We ask them in studies of biodiversity
and systematics, in comparative morphology, in biogeography and when we describe
communities. These questions lead Mayr into discussions of the concept of the
species (which owes so much to him), the principles of classification, numerical
phenetics and cladistics.

“How?” questions are asked in functional morphology and in physiology, but
Mayr chooses to review them only for developmental biology. He summarises the
history of the subject up to the recognition in 1944 that DNA was the carrier of
genetic information, and hastily reviews more recent events. For example, there
is only a single paragraph about Hox genes. He seems not to care much for “how?”
questions.

“Why?” questions arise in evolutionary biology. Mayr analyses Darwin’s
contribution to evolutionary theory, arguing that On the Origin of
Species established five major theories: evolution per se, common descent,
speciation, gradualism and natural selection. He emphasises the importance of
the books of around 1940 which formed the Modern Synthesis, and reviews
subsequent developments, including punctuated equilibria, group selection and
sociobiology.

In a further chapter, Mayr explores the kinds of questions ecologists ask.
His broadbrush historical reviews are impressive throughout the book, but
nowhere more so than here. He points to the great names of ecology and tells us
briefly of the innovations each made. But it is disappointing to find no
discussion of mathematical modelling, and no mention of behavioural ecology
apart from the remark that “most younger ecologists have found ecological
questions involving behavior and life-history adaptation more attractive than
measuring physical constants”. Chapters on human evolution and the origin of
ethics complete the book.

This is a magisterial account of biology, by a great biologist whose wide
interests are not quite wide enough to cover the whole subject in the same
depth. The jacket blurb describes it as suitable for professionals and general
readers alike, but it will mean most to those professionals who already have
some notion of the contributions made by the lesser-known heroes of biology. For
example, on a half page chosen at random I found references to August Weismann,
T. H. Morgan, Richard Goldschmidt, Waddington and Schmalhausen.

The first paperback edition of Mayr’s Evolution and the Diversity of
Life, a collection of his published papers in hard covers in 1976, comes
out at the same time. We are reminded of the diversity and depth of his
contributions to the theory of evolution (especially speciation), to the species
concept and to biogeography, and to the history and philosophy of biology. But
there are limits even to Mayr’s interests in biology. In the introduction, he
writes of the difference between functional biologists who ask “how?” and
evolutionary biologists who ask “why?”, and remarks that functional biology has
never been his field of interest. We can only hope that Mayr’s This is
Biology may soon be joined by a parallel book by a functional
biologist.

DIAGNOSED as suffering from abdominal mesothelioma, Stephen Gould went to the
library to read about the disease. There he found the statistic that the median
time from diagnosis to death was eight months. His case sounded hopeless until
he wondered why the median was given, rather than the mean. The reason, he
surmised, was that a few long-term survivors were skewing the probability of
dying to the right. Plainly, the distribution could not extend far to the left
(no one survives for less than zero time after diagnosis), but it might extend
to the right over many decades. Happily, Gould’s place was on the right tail of
a strongly skewed distribution, and one improved by recent advances in
treatment.

His new book Full House is about strongly skewed distributions and
their implications for the concept of progress, in baseball and evolution. In
baseball, a batting average for the season of 0.400 is exceedingly good. The
best professional players before 1930 frequently achieved 0.400 averages, but no
one has done so since 1941. Gould tells us that we should not conclude that his
countrymen are not the men they used to be (indeed, it would be very odd if
standards in baseball were falling in contrast to the manifest improvement of
performances in athletics). He finds that the authorities have fiddled with the
rules from time to time to keep the mean of the distribution fairly constant at
0.260, so the mean tells us nothing about standards. The standard deviation has
fallen steadily over the past century, however, a trend that he attributes to
improved standards. If the mean is held constant artificially while the standard
deviation falls, the scores of the very best players in successive years can be
expected to fall.

The discussion of baseball may be read for its own sake, but many readers are
likely to value it more for the light it throws by analogy on the largest theme
of Full House, the concept of progress in evolution. Gould attacks the
perversity of the traditional view of progress through an Age of Invertebrates
and an Age of Reptiles to an Age of Mammals in which, despite the name, most
individual organisms are bacteria and most species are beetles. He prefers not
to focus on the mammals at the right tail of the skewed distribution of
complexity, but to look at the whole range.

The modern horse is often thought of as a pinnacle of perfection, the
culmination of evolution of grazing, running mammals. Gould is less
complimentary. He sees Equus as a remnant of a remnant, the sole
surviving genus of a formerly successful family within an order, the
Perissodactyla, that has fallen on hard times. The history of horse evolution is
not a study of progress, but a tale of a promising start leading to ultimate
failure. It starts with Hyracotherium, a terrier-sized animal with many
toes on each foot and low-crowned teeth. A path leads from it through a complex
evolutionary tree of many, diverse species to the sole survivors: large modern
horses with a single toe on each foot and high-crowned grazing teeth.

This may seem like inexorable progress if we ignore fossil genera that are
off the main line of evolution to Equus, but we think of that line as
the main one only because Equus is the genus that happens to have
survived. If the survivor were Nanippus (small and three-toed, it became
extinct only 2 million years ago) our impression of the progress of horse
evolution would be very different.

Gould’s new book is an expanded version of the presidential address that he
gave to the Paleontological Society in 1987. He showed then that apparent trends
in the sizes of foraminiferans and the brains of mammals are better viewed as
expanding variance with a fixed lower limit of size, rather than as trends of
increasing size. Since then others have joined him in refusing to see evolution
as steady progress. Gould tells us how Bruce McFadden in 1988 analysed the
history of the horses and found a complex pattern of branching with many
reversals of direction. He describes how Dan McShea, in a series of papers since
1992, has found no consistent trend to complexity in the evolution of backbones.
He also describes what is perhaps the most telling of these examples— G.
Boyajian and T. Lutz’s analysis in 1992 of the evolution of ammonite shells.
These have sutures that make simple curves in the earliest fossils, but became
on average increasingly complex as evolution progressed. Boyajian and Lutz used
fractal dimension as an objective measure of complexity, and compared ancestors
with their identified descendants. Rather than a general trend to increased
complexity, they found a tangled web of lines in which complexity decreased as
often as it rose, with simple-sutured shells present throughout. If the starting
point is the simplest possible structure, evolution will result in increasing
mean complexity even if lines of descent are random walks.

The same sort of thing happened on a larger scale, in the evolution of the
whole range of living things. The starting point was inevitably simple, probably
the simplest structure consistent with life. Starting from there,
diversification could result only in the appearance of more complex forms. If
increased complexity is seen as advance (which it by no means always is), the
course of evolution must seem like progress. But we should remember that simple
bacteria persist in immense numbers and formidable biomass. The message is
important for professional biologists, but Gould’s new book is as accessible to
intelligent general readers as its predecessors, in all respects but one; a
rudimentary knowledge of baseball will be an advantage.

Gould’s message is that it is commonly misleading to focus on the most
“advanced” or complex organisms at the extreme right of the frequency
distribution. Rather, we should look at the whole distribution, the spread of
excellence. It is an important message with great potential for redirecting our
thoughts, but I hope we will not heed it all the time. We should often think in
the way he advocates, of diversification rather than directional change, but we
should not abandon the adaptationist view that is presented so strongly in
Richard Dawkins’s Climbing Mount Improbable (Review, 27 April, p 48).
There are contexts in which we should focus on the extremes and reflect on the
modern horse as the ultimate (so far) running mechanism. Gould himself focuses
shamelessly on the tail of the frequency distribution when he enthuses about
baseball players.

Like other important statements on evolution, Gould’s message has potential
for misunderstanding. He emphasises that, if there is a limit at one edge of the
range of possibilities, diversification can be expected to shift the mean. A
drunkard staggering on the pavement must eventually fall into the gutter because
the houses on the other side prevent him from falling that way. Creationists
will probably tell us that Gould sees evolution as a drunkard’s random walk, and
has presented a more extreme view than ever before of perfection being generated
by chance. But Gould is not telling us that the diversity of life is the product
of undirected chance, merely that the distribution of complexity that we see is
no evidence of a persistent, directed trend.

The image of debate at an Oxbridge high table recurs frequently in Niles Eldredge’s new book, but the flavour is that of debate between political parties. The government, the Ultra-Darwinist Party, is led by Maynard Smith, with Richard Dawkins as his most vocal colleague. In opposition, the Naturalists are led by Gould, supported by (among others) Eldredge. The book is a sustained attack on Ultra-Darwinist dogma.

The leading topic of debate is the theory of punctuated equilibria, presented by Eldredge and Gould in 1972. They used fossil evidence to argue that species have often persisted unchanged for long periods (for example, ten million years), then given rise to new species very rapidly (for example, in ten thousand years). They saw this “evolution by jerks” (John Turner’s phrase) as a major new insight, and still do.

The Ultra-Darwinists were less impressed. Dawkins wrote in The Blind Watchmaker (1986) that: “The theory of punctuated equilibrium lies firmly within the neo-Darwinian synthesis. It always did. It will take time to undo the damage wrought by the overblown rhetoric, but it will be undone. The theory of punctuated equilibrium will come to be seen in proportion, as an interesting but minor wrinkle on the surface of neo-Darwinian theory.”

Another contentious issue was raised in Gould and Richard Lewontin’s brilliant 1979 paper “The Spandrels of San Marco and the Panglossian Paradigm”. Their thesis was that the Ultra-Darwinist adaptationists had too much faith in the optimising power of natural selection: they were telling “just-so stories”. It’s a good point, and one which I like to expound by comparing trout with squid, both of which seem superbly streamlined and adapted for swimming. But physiological experiments on trout and squid of equal size have shown that the trout swim faster and at lower energy cost. Though squid are plainly not built to the global optimum design for a swimming animal of their size, they may approximate to a local optimum from which improvement in swimming is not possible.

This should not surprise us. If I set out walking, but always follow the rule of going uphill, it is vaguely possible that I may reach the summit of Ben Nevis (the highest point in Britain), but I am much more likely to end uP at the top of some lesser hill. My final height will depend largely on the point from which I happen to start. Similarly, a fish and a mollusc cannot be expected to evolve to be equally effective swimmers.

Parker and Maynard Smith, writing in Nature in 1990, complained that the Naturalists’ attack on the adaptationist approach had been taken too far. “Any demonstration of the role of chance events – for example, that much molecular variation is selectively neutral, or that unpredictable events have had a major effect on evolution – has been seen as undermining the optimisation approach.”

The palaeontologists’ greatest impact, as seen by Maynard Smith in the 1984 article, had been in establishing the importance of mass extinctions for the course of evolution. Eldredge discusses this topic, and others such as cladistics, sociobiology and species selection. He includes most of the topics that have been contentious in evolutionary biology over the past twenty years. The style is lively and the approach consistently partisan. Views are forcefully expressed, but with too little evidence for us to evaluate them. A more dispassionate analysis could have been more instructive, but would probably have been less entertaining.

THE picture of a boat at the bottom of this page is a design for a submarine.
Its roof is watertight. Water fills goatskin bottles that open through holes
in the hull to the sea outside. The sailor presses them with a lever to
squeeze out water and make the boat more buoyant, or lets them fill to make
it denser, so he can make his submarine rise or sink.

I would not risk sailing in his boat but I have long admired its designer,
Giovanni Borelli (1608-79). He taught in Messina, Pisa and Rome, publishing
books on an epidemic, on physical mechanics and on an erupt-ion of Etna.
His final book (with the submarine in) appeared only after his death. It
has now been translated from Latin to English for the first time.

On the Movement of Animals is a textbook of biomechanics. The submarine
appears as a digression following a discussion of how fishes might use the
gas-filled swim bladders in their body cavities to control depth. Borelli
had a clear grasp of Archi-medes’s principle and applied it both to the
submarine and to the fish. He understood the resolution of forces into components
and used it well in an analysis of pennate muscles. He also knew Galileo’s
work and, as we shall see, the principle of levers, but there his knowledge
of mechanics ended. Newton’s laws of motion were published eight years after
Borelli’s death.

Most of the book is about muscles and how they work the skeleton. For
example, Borelli found that a strong young man could just hold a weight
of 26 pounds at arm’s length (see above). The biceps and brachialis muscles
(ID in the diagram) could then just balance the moment at the elbow. What
force, Borelli asked, must they exert? The hand and forearm weigh about
1 pound and have their centre of gravity at H, halfway along AB, so he took
account of them by adding 2 pounds to the weight R. The line OI is the perpendicular
from the elbow joint to the line of action of the muscles and is one-twentieth
as long as OB. Therefore the muscles must exert (26+2) X 20 = 560 pounds.
In a further experiment, Borelli arranged his young man in a different position,
with the elbow too strongly bent for the brachialis to be used, and calculated
the force in the biceps alone.

So far, it is hard to fault the argument. Unfortunately, Borelli went
on and got into muddles with which some modern students would sympathise.
The muscles are pulling with a force of 560 pounds at I and with an equal,
opposite force at DT. Therefore, he claimed, the total force in them is
1120 pounds, or would be that if each muscle were a single structure. According
to his theory, however, the muscles are built from tiny segments in series,
each no more than a twentieth of a finger’s breadth long. (He had not seen
sarco-meres: these segments were a figment of his imagination.) By adding
up the forces in successive segments he got an enormous total which cannot
be proved wrong (he still predicts the correct force at the ends of the
muscles) but does nothing to help our understanding.

Borelli got into deeper trouble when he tried to calculate the forces
in leg muscles, in a standing jump. He started with a static problem, calculating
muscle forces for a man standing with legs bent, as if about to jump. He
then tried to move to the dynamic case by an argument that confused force
with momentum and reached the spectacular conclusion that the total force
(the sum of the forces in all the leg muscles) was 2900 times body weight.
(Modern calculations give peak forces of about eight times body weight in
the knee extensor muscles, and less in other muscle groups, in a standing
jump.) He was not the first person to apply physical mechanics to animals.
Galileo had argued that large animals need relatively thicker bones; Boyle
had studied the effects of pressure changes in fishes as well as on gases;
and Steno had discussed the geometry of muscles. However, Borelli was the
first to calculate the forces in muscles from the external forces on the
body (still an important activity in biomechanics), and he defined the subject
by writing its first textbook.

He set out the book as a series of propositions and proofs as if it
were a mathematical text, and illustrated it with 18 plates of about 15
diagrams each. In the new edition these plates are supplied as loose leaves
in a pouch in the back cover, making them rather easily lost or stolen.
Paul Maquet has made a most satisfactorily clear translation and has added
a few useful pages of preface and notes.

This book was important in the history of biology. Parts of it are tedious,
but much is fascinating. If I had not been lucky enough to get it to review
I would have asked for a copy for Christmas.

* Springer-Verlag London. Telephone: 01-947 5885.

R. McNeill Alexander is a professor of zoology at the University of
Leeds. His recent book, Dynamics of Dinosaurs and other Extinct Giants,
is published by Columbia University Press.