Darwin’s hesitant doodle let the tree of kinship take shape on a single page. With those branching lines he envisioned a common ancestry for all life, a radical idea that transformed biology and humbled humanity within nature’s web.

In 1837, a young Charles Darwin opened his private notebook and sketched a crude, branching diagram. Above it, he wrote two words: 'I think.' That drawing — a simple tree of lines and forks — would become one of the most important ideas in scientific history. It was the first visual expression of evolution by common descent: the notion that all living things share a single origin, and that life diversifies through gradual change. Each branch represents a lineage, splitting and adapting, some ending, others continuing — all connected. What makes this artifact extraordinary is not its precision, but its honesty. It is a glimpse into the moment an idea is born. A tree, not of kingdoms or gods, but of genes and time. In place of fixity, Darwin imagined flow. Instead of creation as a single act, he saw it as unfolding — slow, continuous, branching. This small sketch cracked open the static view of life that had endured for millennia. And it began with uncertainty, with humility. With 'I think.'