Tree of Life (Darwin's Notebook)
"I think…"—a hesitant notebook sketch where evolution branches into view.
Visual Provenance
This is a direct reproduction of page 36 from Darwin's private Notebook B. The scrawled handwriting and rough sketch are preserved to show the tentative, private nature of this revolutionary idea. It captures the moment of hesitation—'I think'—before the theory of evolution was fully formed.
"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.
Darwin's Notebook B
Scribbled on page 36 of a private notebook, this simple sketch marks the quiet moment when the structure of life on Earth was first visualized as a branching tree rather than a ladder.
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Lyell's Principles
Tree of Life (Darwin's Notebook)
Mendel's Laws
Lyell's Principles
Tree of Life (Darwin's Notebook)
Mendel's Laws
From Beagle Specimens to a Diagram
Notebook B was written soon after Darwin returned from the HMS Beagle voyage. Confronted with fossils, island species, and geographic patterns, he began to suspect that species change over time. The Tree of Life sketch is where these observations crystallize into a single image. The page ties field notes, museum collections, and private doubt into a visual hypothesis.
Origins as Branching, Not Separate Acts
Many earlier origin stories imagine species created individually or arranged in a static hierarchy. Darwin's tree suggests something different: all living forms might descend from shared ancestors, branching again and again. The origin of any one species becomes a local fork in a much longer process. This shift reframes human identity too—placing us as one twig on a vast, shared tree, not as an exception set apart from nature.
From Notebook to Origin of Species
More than twenty years later, Darwin included a more polished branching diagram in On the Origin of Species. By then, the idea of common descent was supported by extensive evidence from fossils, geography, and comparative anatomy. The little "I think" sketch did not prove evolution by itself, but it mapped the path his thinking would follow—and gave later readers a symbol for the theory.
Artifact Profile
Connections Across the Archive
The Tree of Life sketch connects cosmic and planetary origins to the diversity of life. It links deep-time fossils such as stromatolites, Dickinsonia, Tiktaalik, and Archaeopteryx into a single branching story. Later, the formal Tree of Life diagram turns this intuition into a structured biological map. Together, they show that the origin of species is not a single event, but a pattern spreading across the history of Earth.
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Data Source: The Human Archives
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