10 Scientific Images That Changed How We Looked at the World - Popular Mechanics -- Darwin's Phylogenetic Tree of Organisms(Date: 1837) Scrawled in one of his famous notebooks ("red transmutation notebook B"), this is the first branching diagram of the lineage of organisms. The best part is the "I think" scribbled up top. "I think…this may become one of the most important discoveries in human history."
