however, the final shape and size of these structures is

distinctly different and the molecular players involved in limb

identity are reviewed. Finally, the authors raise the interesting

and yet unanswered question of how the tetrapod limb has

been adapted from a common ancestor. This provides a link

with the final chapter, which puts everything previously

discussed into the greater context of evolution. This chapter

emphasizes the re-emergence and coming together of evolu-

tionary and developmental biology in the molecular era,

which now provides researchers with tools to address some

previously intractable questions.

This book gives a succinct overview of vertebrate pattern-

ing and concentrates on areas in which we begin to gain

an understanding of the molecular mechanisms involved.

The account of some pressing questions currently addressed

makes it very up to date and therefore the book should be on

the reading list of any student committed to this exciting and

rapidly progressing research area.

DOI 10.1002/bies.20035

Published online in Wiley InterScience (www.interscience.wiley.com).

The long debate about‘‘spontaneous generation’’

Things Come to Life: Spontaneous Generation Revisited

(2002). Henry Harris pp. 168þ ix. Oxford University Press:

Oxford. Price: £20.00. ISBN 0 19 851538 3.

Reviewed byAdam WilkinsThe BioEssays Editorial Office10/11 Tredgold LaneNapier Street, CambridgeCB1 1HN, UK

The idea of ‘‘spontaneous generation’’, the belief that

living things can arise from inanimate material (either dead

organisms or the earth itself), was one of the most durable

concepts in the history of Western civilization. Although it pre-

dated the writings of Aristotle, it was Aristotle’s endorsement

that legitimized it and helped ensure its acceptance for nearly

two millenia. Indeed, the idea only finally passed out of

mainstream scientific discourse in the 19th century. The great

longevity of the idea of spontaneous generation is impressive

testimony to its tenacity and appeal.

Yet, in most biology courses and texts, the disproof of

spontaneous generation is treated in a rather summary, even

dismissive, fashion as if the idea were a house of cards simply

waiting for the merest touch to collapse. In this traditional

perspective, the disproof of spontaneous generation involved

three crucial, sequential experiments. These were carried

out, respectively, by Francesco Redi (1626–1698), Lazzaro

Spallanzani (1729–1799) and, finally, by Louis Pasteur

(1822–1895). The latter is generally regarded as having

administered the coup de grace.

In this book, Things Come to Life, the distinguished Oxford

cell biologist Henry Harris shows that the history of the idea of

spontaneous generation, and its disproof, are considerably

more complex and interesting than this potted version implies.

As an intrinsic part of this tale, Harris describes the persona-

lities, lives and key beliefs not only of the three traditional

‘‘heroes’’ of the story but those of other individuals who played

important parts in it. Altogether, the serious scientific debate

about spontaneous generation spanned several centuries and

involved many individuals and diverse ideas and approaches.

Intriguingly, as Harris makes clear, the domain of living things

in which spontaneous generation was believed to operate

had already contracted considerably even before the first

experiments. This had taken place simply through common

observation of what did—and did not—occur. If Ovid (43 BC–

17AD), and other Roman contemporaries, saw nothing impro-

bable, for instance, in the idea that frogs could be generated

from mud, by the 1600s, the realm of action of spontaneous

generation had effectively narrowed down to insects. And it

was Redi’s experiment, showing that flies could only come

from rotting meat that had been exposed to other flies, that

provided critical evidence against the operation of sponta-

neous generation even for these animals. It would seem that

the idea that living things could spontaneously arise from non-

living matter was finished.

Yet it soon acquired a new lease on life—the phrase seems

inevitable—with the discovery of microbial forms and, in parti-

cular, the ‘‘animacules’’ (protozoa) that had been revealed by

the use of themicroscope byAnton van Leeuwenhoek (1632–

1723). These new, even smaller forms of life, truly did seem at

first to arise without precursor forms.

Spallanzani’s experiments, involving heat-treated media

kept away from potentially contaminating air, addressed this

issue. They were designed to show that effectively sterilized

media could not support the generation of newmicrobial forms

unless exposed to air carrying the ‘‘germs’’ of pre-existing

microbes. This should have disposed of the idea of sponta-

neous generation of microbial life but the fact that some of

Spallanzani’s treated flasks did become over-runwith bacteria

or molds left room for doubt about his conclusion. In effect, the

heat-resistance of spores ofmanymicrobes raised a technical

Book reviews

590 BioEssays 26.5 BioEssays 26:590–591, � 2004 Wiley Periodicals, Inc.

problem that opponents of the idea of spontaneous generation

had to deal with. Furthermore, those who continued to believe

in the phenomenon argued that the various sterilization treat-

ments harmed the air and that it was this that prevented

development of the organisms in the flasks that did not show

microbial growth. This proposition, in turn, fuelled a debate

about the most appropriate experimental procedures to test

the idea, a debate that went on for more than a century. A

relatively large part of Harris’ account is devoted to this work,

starting with the experiments of John Turbeville Needham, of

Great Britain, in the 1740s.

Pasteur’s experiments, in the 1860s, using heated media

and swan-necked flasks, which effectively prevented the entry

of spores while allowing the diffusion of ‘‘normal’’ air from the

outside, effectively ended this controversy. If, even with

access to non-damaged air, there was no growth in sterilized

culture media, the most reasonable conclusion was that even

microbes must come from previously existing microbes. Yet,

as the history describedbyProfessorHarris shows, therewere

die-hard opponents of Pasteur who refused to accept the

Pasteurian ‘‘proof’’ and who attempted to keep alive the idea

of spontaneous generation, one of whom was active into the

early 1900s. By then, however, the world of scientific ideas,

influenced especially by Virchow’s and Darwin’s arguments

for the continuity of living forms, had moved on. Indeed, as

the author emphasizes, there can never be a single experi-

mental proof of a universal negative. The idea of spon-

taneous generation finally withered away, in the 19th century,

not because Pasteur had categorically put paid to it but

because spontaneous generation simply seemed less and

less probable, as the counter-evidence piled up. In turn, this

meant that fewer and fewer individuals werewilling to continue

the argument.

Yet, as Harris points out in his last chapter, the idea lives on

in one very important area—the study of the origins of life.

Some formof chemical ‘‘spontaneous generation’’ on the early

Earth is, indeed, only one of three possible explanations to

explain the origins of life on this planet and, to most scientists,

it is the most appealing. The other two are seeding (deliberate

or accidental) from some other source in the Universe, which

simply moves the problem to another location without solving

it, or some form of Creation, which moves the question out

of science into the realm of religion. Given that creationist

opponents of evolutionary theory almost inevitably come back

to the problem of the origin of living things as the weak point of

evolutionary biology (though the issue really exists outside

standard Neodarwinian explanations), the problem of sponta-

neous generation persists. It exists, however, in a form that is

quite different from that which pre-occupied post-Rennais-

sance biologists for several centuries, whose history is so

elegantly brought to life in this book by Henry Harris.

DOI 10.1002/bies.20046

Published online in Wiley InterScience (www.interscience.wiley.com).

Book reviews

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