Variation in Mollusca. The most abundant forms vary most.
Brentwood | Essex
My dear Sir
I am much obliged by your very friendly note & for your commendatory remark
upon my monog
As a general rule among the Mollusca I may say that the Genus most abundant in species & the species most abundant in individuals will present the greatest variation as we might naturally expect altho this rule like most others is not without exceptions I have found some species of fossils which are but rare or sparingly exhibited present very great diversity of character this possibly may have arisen from a paucity of individuals in one locality—while another locality which has not been examined or perhaps removed might have furnished them more abundantly & the apparently rare species might not in reality have been so altho no doubt some animals have a greater tendency to change than others or possess a less adaptability to altered conditions by which of course greater permanence of character will be maintained. In regard to the the special genus Lucina there is I believe every possible variation between what are called sectional divisions & the line of demarkation is extremely shadowy fading away in a most evanescent manner. The same may I believe be said of any other extensive Genus such as Helix, Unio, Cerithium, Conus Cypræa &c &c which have been divided into sections but which merge imperceptibly the one into the other
I presume that you are still employed collecting & arranging data for your work of which the essay published is you tell us but an outline I hope that I may live to see it & that you may have health & strength to complete the work you have begun I may add in reference to your remark about the obloquy thrown upon it that it has been a great surprise to me that so much toleration has been accorded to you as seems to me to have been the case I admired your courage in so boldly avowing your opinions
The mistake into which Authors like that of the vestiges fell
by treating the organic world as a chain of developement in a continuous line instead of
as an ever diverging ramification of being had furnished the opponents of the Theory of
the origin of beings by the natural process of production out of a preexisting form with
the means of an easy victory & it was in the midst of the general gratulation at
this ``scotching of the snake'' that your sounder views came upon the world &
backed by the reputation that you had previously so justly acquired
Believe me Dear Sir | Yours very truly | Searles Wood
Feb. 18. 62
Chas Darwin Esq
- f1 3452.f1CD's letter has not been found. The reference is to the first part of Wood's monograph on Eocene bivalves, which was published in December 1861 (S. V. Wood 1861--77).
- f2 3452.f2Evidently CD's question concerned whether species belonging to large genera of molluscs were more variable and wider ranging than those from small genera; this had a bearing on his principle of divergence, first outlined in Origin, pp. 111--30 (see also Kohn 1985). In order to demonstrate the connection between large genera and variable species, CD had already given the results of his extensive tabulation of the genera listed in the floras of various countries in Origin, pp. 54--8. For a discussion of CD's objective in relation to his botanical work, see Browne 1980 and 1983.
- f3 3452.f3In the introduction to Origin (pp. 1--6), CD explained that he regarded the work as an abstract of a larger work yet to be completed. The only part of this larger work that was published during CD's lifetime was Variation (1868). The remaining draft chapters of what CD called his `big book' were published posthumously as Natural selection.
- f4 3452.f4The first edition of Vestiges of the natural history of creation was published anonymously in 1844 ([Chambers] 1844). It argued for a designed progressive evolution of life, and aroused a storm of protest and criticism. Robert Chambers was thought by many to be the author of the work, but this was not confirmed publicly until 1884, well after his death. See Secord 1989 and Secord ed. 1995.