Darwin Beagles

Biology came of age on November 24, 1859, the day Charles Darwin published On The Origin
of Species by Means of Natural Selection. His book presented the first convincing case for
evolution and led the way in the emergence of biology from a bewildering chaos of facts into a
cohesive science. In biology, evolution refers to all the changes that have transformed life on
Earth from its earliest beginnings to the seeningly infinite diversity that characterizes it today.
Darwin addressed the sweeping issues of biology: the great diversity of organisms, their origins
and relationships, their similarities and differences, their geographical distribution, and their
adaptations to the surrounding environment.
Darwin made two points in The Origin of Species. First, he argued from the evidence that
species were not specifically created in their present forms, but had evolved from ancestral
species. Second, Darwin described a mechanism for evolution, which he termed natural selection.
Evolutionary change is based mainly on the interactions between populations of organisms and
their environments. The Origin of Species was truly radical, for not only did it challenge
prevailing scientific views, but it also shook the deepest roots of Western culture. Darwin’s view
of life contrasted sharply with the conventional paradigm of an Earth only a few thousand years
old, populated by immutable (unchanging) forms of life that had been individually made by the
Creator during the single week in which he formed the entire universe. Darwin’s ideas subverted a
world view that had been taught for centuries.

THE VOYAGE OF THE BEAGLE — Darwin was 22 years old when he sailed from England
with the Beagle in December 1831. The primary mission of the voyage was to chart poorly
known stretches of the South American coastline. While the crew of the ship surveyed the coast,
Darwin spent most of his time on shore, collecting thousands of specimens of the exotic and
exceedingly diverse fauna and flora of South America.
As the ship worked its way around the continent, Darwin was able to observe the various
adaptations of plants and animals that inhabited such diverse environments as the Brazilian
jungles, the expansive grasslands of the Argentine pampas, the desolate lands of Tierra del Fuego
near Antartica, and the towering heights of the Andes Mountains. He realized that the fauna and
flora were very distinct from the life forms of Europe. The plants and animals living in temperate
regions of South America were taxonomically closer to species living in tropical regions of that
continent than to species in temperate regions of Europe. Furthermore, the South American
fossils that Darwin found, though clearly different from modern species, were distinctly South
American in their resemblance to the living plants and animals of that continent. Darwin was
perplexed by the peculiarities of the geographical distribution of species.
A particularly puzzling case of geographical distribution was the fauna of the Galapagos
Islands, which lie on the Equator about 900 km. west of the South American coast. Most of the
animal species on the Galapagos live nowhere else in the world, although they resemble species
living on the South American mainland. Among the birds Darwin collected on the Galapagos
were 14 types of finches that, although quite similar, seemed to be different species. Some were
unique to individual islands, while other species were distributed on two or more islands that were
close to each other. Darwin wondered about the relationships of the island finches to one another
and to the finches on the mainland, which were different.
By the time the Beagle sailed from the Galapagos, Darwin had read Lyell’s Principles of
Geology. Darwin was doubting the church’s position that the Earth was static and had been
created only a few thousand years ago. By acknowledging that the Earth was very old and
constantly changing, Darwin had taken an important step toward recognizing that life on Earth
had also evolved. He would soon realize that evolution was the only rational explanation for the
relationships between the species he had collected, particularly those from the Galapagos Islands.

At the time Darwin collected the Galapagos finches, he was not sure whether they were
actually different species or merely varieties of a single species. Soon after returning to England in
1836, he learned from ornithologists (bird specialists) that the finches were indeed separate
species. He began to reassess all that he had observed during the voyage of the Beagle and in
1837 began the first of several notebooks on the origin of species.

Darwin began to perceive the origin of new species and adaptation as closely related
processes. A new species would arise from an ancestral form by the gradual accumulation of
adaptations to a different environment. For example, if one species became fragmented into
several localized populations isolated in different environment by geographical barriers, the
populations would diverge more and more in appearance as each adapted to local conditions,
gradually, over many generations, becoming dissimilar enough to be designated separate species.
This is apparently what happened to the Galapagos finches. Among the differences between the
birds are their beaks, which are adapted to the specific foods available on their home islands.
Darwin anticipated that explaining how such adaptations arise was essential to understanding
evolution.

Bibliography
1. Biology by Neil A. Campbell C.1986
2. Aol.www.charlesdarwin.com
Science