was written in 1842
agrees with an entry in my fathers Diary:--

"1842. May 18th went to Maer. June 15th to Shrewsbury, and on 18th to
Capel Curig.... During my stay at Maer and Shrewsbury (five years after
commencement) wrote pencil sketch of my species theory." Again in a
letter to Lyell (June 18, 1858) he speaks of his "MS. sketch written out
in 1842{18}." In the _Origin of Species_, Ed. i. p. 1, he speaks of
beginning his speculations in 1837 and of allowing himself to draw up
some "short notes" after "five years' work," _i.e._ in 1842. So far
there seems no doubt as to 1842 being the date of the first sketch; but
there is evidence in favour of an earlier date{19}. Thus across the
Table of Contents of the bound copy of the 1844 MS. is written in my
father's hand "This was sketched in 1839." Again in a letter to Mr
Wallace{20} (Jan. 25, 1859) he speaks of his own contributions to the
Linnean paper{21} of July 1, 1858, as "written in 1839, now just twenty
years ago." This statement as it stands is undoubtedly incorrect, since
the extracts are from the MS. of 1844, about the date of which no doubt
exists; but even if it could be supposed to refer to the 1842 Essay, it
must, I think, be rejected. I can only account for his mistake by the
supposition that my father had in mind the date (1839) at which the
framework of his theory was laid down. It is worth noting that in his
Autobiography (p. 88) he speaks of the time "about 1839, when the theory
was clearly conceived." However this may be there can be no doubt that
1842 is the correct date. Since the publication of _Life and Letters_ I
have gained fresh evidence on this head. A small packet containing 13
pp. of MS. came to light in 1896. On the outside is written "First
Pencil Sketch of Species Theory. Written at Maer and Shrewsbury during
May and June 1842." It is not however written in pencil, and it consists
of a single chapter on _The Principles of Variation in Domestic
Organisms_. A single unnumbered page is written in pencil, and is headed
"Maer, May 1842, useless"; it also bears the words "This page was
thought of as introduction." It consists of the briefest sketch of the
geological evidence for evolution, together with words intended as
headings for discussion,--such as "Affinity,--unity of type,--foetal
state,--abortive organs."

{18} _Life and Letters_, ii. p. 116.

{19} _Life and Letters_, ii. p. 10.

{20} _Life and Letters_, ii. p. 146.