Charles Darwin relied on his notebooks. In them, he jotted private ideas, questions, fragments of conversations, and sketchy drawings related to his thinking on "transmutation"—what we now call "evolution." The notebooks reveal a great mind homing in on a great idea: Plants and animals are not fixed and unchanging.…

Analysis of fossil collagen shows that unusual South American ungulates (like Toxodon platensis, seen here) were more closely related to horses and their allies than to other living placental mammals. Illustration © Peter Schouten

We may have Charles Darwin's children to thank for the surviving handwritten pages of the naturalist's "On the Origin of Species" manuscript. Most of the original 600 pages are lost, and of the 45 pages that exist today, many were repurposed by Darwin's brood of 10 children as art supplies.

Tracing the evolution of Charles Darwin's thoughts about evolution is becoming an increasingly accessible project, thanks to a growing cache of publicly available digitized Darwin manuscripts on the Museum's site.