Evolution's Rocky Beginnings
Charles Darwin, Geologist. Sandra Herbert. xxii + 485 pp.
Cornell University Press, 2005. $39.95.
In February 1859, Charles Darwin received the Wollaston Medal, the
highest honor bestowed by the Geological Society of London, in
recognition of his scientific contributions to the field. He was
ecstatic; he had reached the pinnacle of geology. Eight months
later, in November 1859, he published On the Origin of Species
by Means of Natural Selection. Forever after, Darwin would
be famous as a biologist. Sandra Herbert sets out to explain how the
two sides of his scientific life and work were related and why we
should remember Darwin the geologist.
Charles Darwin (1809-1882) grew up with all the material advantages
of a gentle-born Englishman. He also enjoyed certain
"propitious circumstances," as Herbert describes them,
that help to explain why a young man of means with an insatiable
curiosity about the natural world would choose geology as his
vocation. Europe was at peace following the devastating Napoleonic
Wars, and Britain, the most prosperous and powerful country, ruled
the waves. Scientific exploration was the order of the Admiralty,
and so Darwin could hope to emulate the Pacific voyages of Captain
James Cook. He also wanted to visit the tropics, as had Alexander
von Humboldt, a naturalist whose method of exploration and style of
writing influenced Darwin greatly. Like Humboldt, Darwin would
combine physical and biological investigations.
Darwin's study of geology began at Edinburgh University, where his
father sent him to study medicine in 1825. Darwin showed little
interest in that profession and two years later "went up"
to the University of Cambridge to prepare for the Anglican ministry.
It was there under the mentorship of John Stevens Henslow, professor
of mineralogy and later professor of botany, that Darwin learned how
different were the theories of the Earth being taught at Edinburgh
and Cambridge. As Herbert makes clear, geology in the 1820s and
1830s was a field full of big debates. This intellectual excitement
and the chance to make a lasting contribution attracted the
ambitious young Darwin. Such eagerness caught the attention of
others at Cambridge, namely Adam Sedgwick, professor of geology.
Sedgwick took Darwin to Wales in 1831, where he learned to do
fieldwork and to feel joy in making scientific discoveries.
What made Darwin an active researcher, not simply a well-grounded
student, was his round-the-world voyage aboard H.M.S.
Beagle (1831-1836). Herbert recounts in colorful detail
(both in words and pictures) the five years Darwin spent exploring
South America and the islands of the Atlantic and Pacific. She also
concentrates on what Darwin read during the voyage and thereby is
able to show how Darwin observed, collected samples and interpreted
these data in response to his growing knowledge and experience. This
careful reconstruction displays Herbert's impressive mastery of all
that Darwin wrote (letters, diaries, notebooks, publications) and
all that has been written about him. Such comprehensiveness can, at
times, leave a reader in a tangled bank of names and commentaries.
Herbert calls her thick description and topical approach a
"sinuous" history. Hence she picks up the three volumes of
Charles Lyell's Principles of Geology (1830-1833) just as
Darwin did during the voyage. In later chapters she returns to Lyell
again and again as Darwin worked through his notes, wrote up his
results and sharpened his ideas.
The voyage of the Beagle supplied Darwin with a lot more
than specimens and observations—it gave him an identity. He
became a scientific author. After his return to England, he
published three books on geology and more than a dozen articles. In
these works, he developed a grand theory of the Earth. Darwin tried
to explain geological phenomena by the elevation and subsidence of
the Earth's crust. Herbert refers to Darwin's research on the causes
and consequences of vertical movements as "simple"
geology. (Simple meant "having one mechanism or
operation," not "unsophisticated.") This work marked
Darwin as a bold theorist. It also put him outside the mainstream of
geological research, which, as Herbert explains, focused on the
identification, ordering and correlation of strata. Darwin was not
so much interested in stratigraphy as he was in volcanoes, mountains
and earthquakes. He was a structural theorist on a continental scale.
Darwin's most successful application of simple geology and his most
lasting contribution to the science was his explanation of the
origin of coral reefs. (They build up on the sides of slowly
subsiding seamounts.) He then tried to apply his theory of vertical
crustal movements to account for the parallel roads of Glen Roy,
Scotland. This proved to be his decisive failure. Soon after he
propounded his explanation, the roads were reinterpreted as remnants
of glaciers. Ice, not the rise and fall of the crust, explained the
phenomena. Darwin's grand theory of the Earth did not work, and for
Herbert, this was a key factor in ending his active career as a geologist.
Another factor, of course, was evolution. By the early 1840s, Darwin
was devoting his full energy to the species question. In developing
his theory of natural selection, he had to work against an apparent
lack of geological evidence; nowhere in the fossil record was there
a clear example of the transmutation of one species into another.
Herbert, too, has to work against an apparent lack of evidence; the
connection between Darwin's geology and his biology is not obvious.
Herbert, however, makes a strong case for reading deeper into the
ways Darwin understood changes in time and changes in space. Rocks
rise and sink; species appear and go extinct. What happens on one
part of the globe is connected to another. Gradually, over long
periods, small changes can accumulate into great effects. Continents
will emerge, as do new animals and plants. For Herbert, what geology
gave to Darwin was a gradualist's sense of time and a global
perspective. For historians, what Herbert has presented is a broader
view of the science of Charles Darwin.