Charles Darwin in his most famous work, surprisingly, almost no mention of the fossil that he picked up in South America , apart from brief references in 'Introduction.
"WHEN on board HMS 'Beagle,' as naturalist, I was much struck with Certain facts in the distribution of the Inhabitants of South America, and in the geological relations of the present to the past Inhabitants of That continent. These Seemed to me facts to throw Some light on the origin of species-that mystery of mysteries, as it Has Been Called by one of Our greatest philosophers. "
"WHEN on board HMS 'Beagle,' as naturalist, I was much struck with Certain facts in the distribution of the Inhabitants of South America, and in the geological relations of the present to the past Inhabitants of That continent. These Seemed to me facts to throw Some light on the origin of species-that mystery of mysteries, as it Has Been Called by one of Our greatest philosophers. "
Fig.1. Il fossile che Darwin attribuisce a un piccolo mammifero roditore, dalla formazione di Monte Hermoso nell´Argentina (Pliocene inferiore), da DARWIN 1840, Fossil Mammalia Pl. XXXII. Al contrario un intero capitolo di " Origin of Species " è dedicato alle lacune del record geologico è l'apparente mancanza di fossili di transizione. Questa discrepanza era nota già a Lamarck, che aveva postulato (e formulato una teoria) che le specie non sono fisse, è i limiti discreti tra di loro sono il risultato di una preservazione incompleta di forme di transizioni durante l'atto di fossilizzazione. Questa idea verra adoperata anche da Darwin (" Chapter IX, on the imperfection of the geological record ").
A meta del 19. secolo era chiaro che specie si potevano estinguere, ma rimase il problema di come queste estinzioni avvengono e come dopo una di queste fasi il pianeta veniva ripopolato. Anche Darwin durante il suo viaggio sul Beagle, ancora prima della formulazione della sua teoria di trasmutazione, si chiedeva se delle specie possono morire e in che modo vengono rinate (escludendo una creazione divina), un'idea che era stata anche ipotizzata dal geologo italiano Giovanni Battista Brocchi nel 1814 (dimostrando ancora una volta il profondo cambio di pensiero in quei decenni).
Osservando fossili simili all'odierna Mara ( Dolichotis patagonum ), A South American rodent that resembles a small deer, Darwin thought that species were replaced in time by similar forms together (Owen will determine the fossils belonging to a relative of today 's tuco-tuco tucutucu or small rodent of the genus Ctenomys ). However, these forms remains
concrete entities in space and time, for example at Warri, the fox endemic and extinct Darwin could still look on the Falkland Islands, wrote in 1834 "... indisputable proof of the ITS individuality as a species ..." . Darwin start working on his theory after his return home, and in a first attempt to try to reconcile his view of the species as concrete entities with a possible jump through transmutation of species specific, ie, a species could give "birth" to a new species within a short time.
Continued ...
Fig.2. The three possible relationships of fossil forms of a certain horizon and recently elaborated by Darwin between 1832 and 1835. In case A, the giant sloth / armadillo giant extinct and are replaced by the recent species. The species does not have a direct connection between them. In molluscs (case C), Darwin observed a continuum of species that persist through geological time. The case is B an intermediate version of the first two, the fossil remains of the peculiar South American rodents are relatively modern with rodent species, which occur over geological time (ELDREGE 2008). Bibliography:
DARWIN, CR (1859): On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London: John Murray. [1st edition]
Darwin, CR ed. (1840): Fossil Mammalia Part 1 No. 4 of The zoology of the voyage of HMS Beagle. By Richard Owen. Edited and superintended by Charles Darwin. London: Smith Elder and Co.
Eldredge, N. (2009): A Question of Individuality : Charles Darwin, George Gaylord Simpson and Transitional Fossils. Evo. Edu. Outreach 2(1): 150-155
ELDREDGE, N. (2008): Experimenting with Transmutation: Darwin, the Beagle, and Evolution. Evo. Edu. Outreach 2(1): 35-54
QUATTROCCHIO, M.E.; DESCHAMPS, C.M.; ZAVALA, C.A.; GRILL, S.C. & BORROMEI, A.M. (2009): G eology of the area of Bahia Blanca, Darwin´s view and the present knowledge: a storay of 10 million years. Revista de la Asociacion Geologica Argentina 64(1): 137-146
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