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Charles Darwin's very radical ideas on the structure
of the living world transformed biology from a collection of
curious but disconnected facts into a vigorous and unified science.
His theory of evolution by natural selection originated during
a five-year voyage around the world as a naturalist on board
HMS Beagle under the command of captain Robert FitzRoy.
The voyage had three missions, two official and one unofficial.
The official missions were to map the east and west coasts of
South America, and to complete a series of chronometric readings
while circumnavigating the globe. The chronometric readings
are related to the the way in which navigators determine longitude.
If a sailor knows what local time corresponds to noon Greenwich
time, then he simply takes a sighting on the angle of the sun,
knowing that at noon, the sun is directly overhead in Greenwich.
It is then a simple calculation to determine how many degrees
he has travelled from Greenwich. The unofficial mission was
to repatriate three Tierra del Fuegian natives captured by FitzRoy
during the previous voyage of the Beagle. Fuegians were
normally hostile to shipwrecked sailors and FitzRoy hoped that
by educating these captives and teaching them English manners,
they would ultimately convert their countrymen to developing
a friendly attitude towards sailors.
FitzRoy was terrified of the lonliness and isolation
that he would face as captain (the captain on the previous voyage,
on which FitzRoy was first mate, committed suicide, and FitzRoy
himself was emotionally high-strung and mentally unstable).
As captain of an English ship, he would be restricted from any
close relationships with his crew. He therefore hit upon the
idea of inviting a gentleman of appropriate social standing
to be his guest and companion. In return, the companion would
have a rare opportunity to visit exotic locales and see new
and wonderous sights. The position was offered to the naturalist
and clergyman Leonard Jenyns, who declined because of his parish
responsibilities. Jenyns recommended John Henslow, a famed botanist
and clergyman, who declined because of his family situation.
Henslow, who was also Darwin's friend and mentor, recommended
Darwin as the best qualified person who would be likely to accept.
Darwin's father, Robert, was most unhappy about
the situation and forbade him from accepting the offer. But
he did leave an out by saying that if Charles could find one
reasonable man to convince him otherwise, then he would allow
Charles to go. Darwin enlisted the aid of his uncle, Josiah
Wedgewood, and finally received his father's blessing. The Beagle
departed on 27 December 1831 on what was meant to have been
a three-year voyage, and returned on 2 October 1836. On 16 September
1835 the Beagle reached the Galapagos Archipelago, a
cluster of islands on the equator 600 miles west of South America.
During his five weeks in the Galapagos, Darwin
found the giant tortoises that differed from one another so
greatly that anybody with half an eye could immediately say
which island they came from. Two forms of iguanas lived in the
islands. Each type had affinities with the common South American
green iguana, yet they had adapted so profoundly to different
ecologic niches in the islands that they had evolved into separate
genera. Conolophus, adept at living on the arid islands
and feeding on the sharp-spined Opuntia cactus became the land
iguana, while Amblyrhynchus, with its flattened tail
for swimming, its strong claws for hauling itself out on the
water, and its blunt, shortened snout for scraping algae off
of rocks, became the marine iguana. Moreover, many islands developed
their own races of these unusual lizards. Many of the birds
that Darwin found, especially the land birds, were endemic species
found nowhere else on earth. Here were thirteen different types
of finches whose beeks were modified to different sub-environments
on the islands.
The Galapagos islands were volcanic in nature
and relatively recently formed, Darwin reasoned, and the animals
that dwelt there had to have come from someplace else. Those
most closely resembling the Galapagos community were the animals
that lived closest to the islands on the mainland. But they
were not the same animals. Why?
Why? That was the question that plagued Darwin.
Why? Eight years after his return, Darwin wrote to his close
friend and colleague, Sir Joseph Hooker: "At last gleams
of light have come, and I am almost convinced (quite to the
contrary to the opinion I started with) that species are not
(it is like confessing a murder) immutable." According
to Genesis, God created all plants and animals, and they have
not changed significantly since that time. Yet the only way
that Darwin could explain all of his observations was that they
had indeed changed. The pivotal role of the Galapagos islands
in shaping Darwin's new world view is clear from a passage in
his ornithological notebooks:
"If there is the slightest foundation
for evolution, the zoology of the Galapagos will be well worth
examining..."
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