 Darwin’s theory first took written form in reflections in a series of notebooks begun during the latter part of the Beagle voyage and continued after the return of the Beagle in October of 1836. His reflections on the possibility of species change are first entered in March of 1837 (“Red Notebook”) and are developed in the other notebooks (B–E) through July of 1839 (Darwin 1836–1844 [1987]; Hodge 2013a, 2003). Beginning with the reflections of the third or “D” Notebook, composed between July and October of 1838, Darwin first worked out the rudiments of what was to become his theory of natural selection. In the parallel “M” and “N” Notebooks, dating between July of 1838 and July of 1839, and in a loose collection called “Old and Useless Notes”, dating from approximately 1838–40, he also developed many of his main ideas on human evolution that would only be made public in the Descent of Man of 1871 (see below).