Darwin's Other Books: “Red” and “Transmutation” Notebooks, “Sketch,” “Essay,” and Natural Selection

Study of Darwin's unpublished works, freely available on-line through the American Natural History Museum, reveals the origins of his thoughts on evolution

Brocchi, Darwin, and Transmutation: Phylogenetics and Paleontology at the Dawn of Evolutionary Biology

Giambattista Brocchi's (1814) monograph (see Dominici, Evo Edu Outreach, this issue, 2010) on the Tertiary fossils of the Subappenines in Italy—and their relation to the living molluscan fauna—contains a theoretical, transmutational perspective ("Brocchian transmutation"). Unlike Lamarck (1809), Brocchi saw species as discrete and fundamentally stable entities. Explicitly analogizing the births and deaths of species with those of individual organisms ("Brocchi's analogy"), Brocchi proposed that species have inherent longevities, eventually dying of old age unless driven to extinction by external forces. As for individuals, births and deaths of species are understood to have natural causes; sequences of births and deaths of species produce genealogical lineages of descent, and faunas become increasingly modernized through time. Brocchi calculated that over 50% of his fossil species are still alive in the modern fauna. Brocchi's work was reviewed by Horner (1816) in Edinburgh. Brocchi's influence as a transmutational thinker is clear in Jameson's (1827) "geological illustrations" in his fifth edition of his translation of Cuvier's Theory of the Earth (read by his student Charles Darwin) and in the anonymous essays of 1826 and 1827 published in the Edinburgh New Philosophical Journal—which also carried a notice of Brocchi's death in 1827. The notion that new species replace older, extinct ones—in what today would be called an explicitly phylogenetic context—permeates these essays. Herschel's (1830) discussion of temporal replacement of species and the modernization of faunas closely mirrors these prior discussions. His book, dedicated to the search for natural causes of natural phenomena, was read by Charles Darwin while a student at Cambridge. Darwin's work on HMS Beagle was in large measure an exploration of replacement patterns of "allied forms" of endemic species in time and in space. His earliest discussions of transmutation, in his essay February 1835, as well as the Red Notebook and the early pages of Notebook B (the latter two written in 1837 back in England), contain Brocchi's analogy, including the idea of inherent species longevities. Darwin's first theory of the origin of species was explicitly saltational, invoking geographic isolation as the main cause of the abrupt appearance of new species. We conclude that Darwin was testing the predicted patterns of both Brocchian and Lamarckian transmutation as early as 1832 at the outset of his work on the Beagle

Chelicerata, Merostomata

17 p. : ill. ; 24 cm.Includes bibliographical references (p. 17)."The functional morphology of burrowing was investigated in Limulus polyphemus with particular attention paid to the role played by the dorsal setae and prosomal shape. The burial process can be broken down into four discrete stages. Stage 1 involves active burial by downward flexion of the prosoma and a promotor-remotor swing (normal walking) by the prosomal legs. Sand is forced over the prosoma and anterior one-third of the opisthosoma, and a channel between these two structures is kept clear. Stage 2 involves no further burial, but rather active intake of water through one or both channels, deflection of the current back toward the gills underneath the opisthosoma, and expulsion of the current under one or both posterior opisthosomal projections. Stage 3 is the final burial phase and is effected both by forward walking and forceful flapping of the opisthosoma into the substratum; burial ceases when the last posterior opisthosomal projection is finally buried. The telson is covered throughout this process. Stage 4 is a long period of dormancy. The dorsal setae, distributed on the margins of the carapace, are mechanoreceptors that aid in keeping the organism buried. Their action is integrated with all other anatomical and behavioral aspects of burrowing, so that burrowing cannot be entirely disrupted by suppression of the tactile setae. Prosomal shape is at least partially explicable in terms of burrowing efficiency. The frontal arch is a necessary concomitant to a mode of burrowing that utilizes only normal promotor-remotor (walking) activity of the appendages; the arch effectively presents a horizontal edge to the substratum upon flexure of the prosoma of approximately 15 degrees. The high angle of slope of the margin of the carapace creates a thick wall of sediment that covers the rest of the body and allows burial within a minimum amount of space. The coaxial exite of the sixth prosomal appendage is a curved structure that probably deflects the current of water entering at the channel back toward the opisthosomal gill appendages, although they do not carry out this function alone. It may or may not be used to clean the gills, which is the function usually attributed to it. Limulus polyphemus possesses many anatomical similarities with trilobites. Detailed knowledge of the functional morphology of L. polyphemus may, if carefully applied, serve as a model for interpretation of trilobite morphology hitherto incompletely understood. In particular, the nature and role of the sensory dorsal setae and the functional aspects of the anterior arch in L. polyphemus appear to have a direct bearing on the interpretation of closely comparable structures in certain trilobites"--P. 16-17

How does genetic diversity change towards the range periphery? An empirical and theoretical test

Question: How does genetic diversity change as one moves along a species' range, towards the periphery? Previous work shows contradictory evidence for an increase, decrease or no clear trend along the range