This figure was drawn in Darwin’s Notebook “B” in 1837, a year after his return from the Beagle voyage. His accompanying note states, “case must be that one generation then should be as many living as now…To do this & have many species in same genus (as is). REQUIRES extinction.” This example, among others, shows that Darwin started to formulate his ideas about "descent with modification" almost immediatley after the voyage, although it took him another two decades to finally publish his full-blown theory.
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