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Darwin's Diary

Introduction | 1809-1825 | 1826-1829 | 1831 | 1832 | 1833 | 1835 | 1836
1837 | 1838 | 1842-1854 | 1856 | 1858-1859 | 1881 | 1882


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

"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."

"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?

July 1837 (Birth of a Theory)

As experts continue sorting through the Beagle collection, Darwin is driven to bold thoughts.

"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."

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?

"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."

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."

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?

"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."

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."

-> Go to 1838


Introduction | 1809-1825 | 1826-1829 | 1831 | 1832 | 1833 | 1835 | 1836
1837 | 1838 | 1842-1854 | 1856 | 1858-1859 | 1881 | 1882

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