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Darwin's Diary |
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Introduction | 1809-1825 | 1826-1829 | 1831 | 1832 | 1833 | 1835 | 1836
1837 | 1838 | 1842-1854 | 1856 | 1858-1859 | 1881 | 1882 |
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January-March 1837 (Birth of a Theory)
Early in January, Darwin gives a group of poorly labeled birds
collected in the Galapagos to John Gould at London's Zoological Society. Gould is
one of several renowned naturalists eager to look at Darwin's collections. Darwin
thinks the birds are a jumbled mix of finches, wrens, and blackbirds, and of little
importance.
Six days later, Darwin returns to hear that his birds are not a
jumble after all. Their beaks had misled him into thinking they were very different
types of birds. In fact, they are
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"a most singular
group of finches, related to each other in the structure of their beaks, short
tails, form of body, and plumage: there are thirteen species ... all ... peculiar
to this archipelago."
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"The most curious
fact," Darwin observes, "is the perfect gradation in the size of the beaks in
the different species of geospiza [finch]." With different beaks and behavior,
Darwin's finches feed on different foods. Some easily crack hard nuts; others
peck insects out of plants. One species even rides on the back of iguanas, pecking
at them to feed on their blood.
A few weeks later, Gould relays more surprises. Darwin had
assumed that the mockingbirds he collected in the Galapagos were different varieties
of the same species. Now Gould tells him that they are all representatives of
distinct species, each inhabiting its own island.
The news helps lead Darwin to a radical idea: Could varieties of
birds, isolated on separate islands, somehow turn into new species?
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July 1837 (Birth of a Theory)
As experts continue sorting through the Beagle collection,
Darwin is driven to bold thoughts.
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"I [was] deeply
impressed by ... great fossil animals covered with armour like that on the
existing armadillos ... and ... by the ... character of most of the productions
of the Galapagos archipelago ... the manner in which they differ slightly on
each island of the group; none of these islands appearing to be very ancient
in a geological sense."
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In South America,
the fossil fields are packed with creatures distinct yet similar to the species
of today. In the Galapagos, distinct-yet-similar species inhabit different islands.
Could the similarities in appearance indicate actual blood relationships, like
those on a family tree?
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"It was evident that
such facts as these, as well as many others, could be explained on the supposition
that species gradually become modified; and the subject haunted me."
"In July I opened my first note-book for facts in relation to
the Origin of Species, about which I had long reflected, and never ceased working
on it for the next twenty years."
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In his first notebook
on the subject, Darwin sketches out a branch on what he envisions as the "tree of
life." He imagines an enormous tree, encompassing all of life on Earth, past and
present. New species branch off from their ancestors. Extinct species are like
"terminal buds dying." And at the root lies the common ancestor from which all
life sprang. Next to the sketch, Darwin writes, "Heaven knows whether this agrees
with Nature."
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1837 and onward (Birth of a Theory)
Gentlemen could admire the breeders' art at an annual pigeon
show at the Freemason's Tavern. But Darwin ventured far beyond the confines of
his social class to gather information, fraternizing with working-class fanciers
in their taverns. Darwin later keeps a pigeon roost of his own with baldheads,
pouters, fantails, and more.
Breeders "select" for traits in animals that they find
appealing. If pigeon breeders could derive fancy breeds from one common species,
couldn't nature evolve different species from one ancestral species?
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"It appeared to me
that ... by collecting all facts which bore in any way on the variation of animals
and plants under domestication ... some light might perhaps be thrown on the whole
subject [of the origin of varieties and species in nature] ...
"I ... collected facts on a wholesale scale ... by printed
inquiries, by conversation with skillful breeders and gardeners, and by extensive
reading. When I see the list of books of all kinds which I read and abstracted ...
I am surprised at my industry.
"I soon perceived that selection was the keystone of
man's success in making useful races of animals and plants. But how selection
could be applied to organisms living in a state of nature remained for some time
a mystery to me."
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Could nature "select"
for the traits of animals in the wild? Darwin notes, "organisms of every kind are
beautifully adapted to their habitats of life, -- for instance, a woodpecker or
tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I had always
been much struck by such adaptations."
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-> Go to 1838
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Introduction | 1809-1825 | 1826-1829 | 1831 | 1832 | 1833 | 1835 | 1836
1837 | 1838 | 1842-1854 | 1856 | 1858-1859 | 1881 | 1882 |
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