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Darwin’s 1837 notebook sketch headed “I think”
Tree of Life (Darwin's Notebook), 10 of 10 in OriginsIdea 1 of 6: "I think" and the First Branching
Origins 001—009

Tree of Life (Darwin's Notebook)

1837 CE

From the archiveOrigins10 artifacts
From the record · 01 / 06

"I think" and the First Branching

At the top of the page, Darwin writes "I think"—not "I know" or "It is so." Beneath it, he draws a trunk that splits into branches, which split again. Some branches end abruptly; others continue. The diagram is rough, but its meaning is clear: species are related like members of a growing, dividing tree. This is the opposite of a ladder of progress. It is a map of kinship.

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At the top of the page, Darwin writes "I think"—not "I know" or "It is so." Beneath it, he draws a trunk that splits into branches, which split again. Some branches end abruptly; others continue. The diagram is rough, but its meaning is clear: species are related like members of a growing, dividing tree. This is the opposite of a ladder of progress. It is a map of .