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3 Posts tagged with the charles_darwin tag
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Ian Kitching, together with colleagues at the University of California, National University of Singapore and the University of Erlangen, Germany, has published a review paper charting the history of Charles Darwin’s prediction of coevolution between a long-spurred orchid, Angraecum sesquipedale, and a long-tongued hawkmoth, Xanthopan morganii praedicta, from Darwin’s first observations in 1862 to the final demonstration of successful pollination in the wild in 2004.

 

Angraecum NaturalHistoryMuseum_PictureLibrary_012880_IA.jpg

Angraecum Sesquipedale

 

Darwin wrote in his 1862 work On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing:

 

I fear that the reader will be wearied, but I must say a few words on the Angræcum sesquipedale, of which the large six-rayed flowers, like stars formed of snow-white wax, have excited the admiration of travellers in Madagascar. A whip-like green nectary of astonishing length hangs down beneath the labellum. In several flowers sent me by Mr. Bateman I found the nectaries eleven and a half inches long, with only the lower inch and a half filled with very sweet nectar. What can be the use, it may be asked, of a nectary of such disproportional length? We shall, I think, see that the fertilisation of the plant depends on this length and on nectar being contained only within the lower and attenuated extremity. It is, however, surprising that any insect should be able to reach the nectar: our English sphinxes have probosces as long as their bodies: but in Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches!

 

A moth with such a long proboscis, Xanthopan morganii praedicta, was not described until 41 years after the publication of this book, and it was not observed to visit Angraecum until 1992, with further work to prove pollination since then.  Ian and colleagues discuss issues of co-evolution and predation in this excellent paper.

 

Xanthopan morganii praedicta NaturalHistoryMuseum_PictureLibrary_037535_IA.jpg
Xanthopan morganii praedicta


Arditti, J., Elliott, J., Kitching, I.J. & Wasserthal, L.T. 2012. ‘Good Heavens what insect can suck it’ – Charles Darwin, Angraecum sesquipedale and Xanthopan morganii praedicta. Botanical Journal of the Linnean Society 169: 403-432.

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Charles Darwin spent much of his later life at Downe in Kent: thinking, writing and experimenting in an emphatically rural landscape.  But he retained an interest in marine animals, a fascination that developed in his early years at university and during his extended voyage around the world on HMS Beagle.


Professor Phil Rainbow (Keeper of Zoology) has published a keynote presentation in the journal Marine Ecology on the influence of marine biology on Charles Darwin - and the influence of Darwin on marine biology.

 

Darwin made his first forays into the world of marine biology as a medical student in Edinburgh from 1825 to 1827. He came under the influence there of the Lamarckian Robert Grant, and developed an understanding of the simple organisation of the early developmental stages of marine invertebrates. Yet Darwin could not accept Lamarckian transmutation - a complex set of ideas on evolution that preceded the idea of natural selection.  (Lamarck was a French scientist who, among other ideas, argued that a characteristic [such as larger muscles as a result of frequent exercise] acquired during an organism's life would be passed on to descendants and resulted in evolutionary change: Darwin's later development of natural selection as an explanation for evolution discredited Lamarck's ideas.)

 

The voyage of the Beagle gave him intense exposure to a wide range of marine environments around the world and led to Darwin's perceptive theory on the origin of coral reefs, an origin still mainly accepted today. This theory was linked closely to the uniformitarianism (gradual geological change over millions of years) of the geologist Charles Lyell, depending on the slow, gradual growth of billions of coral polyps keeping pace at sea level with slow sinking of land to produce an atoll.

 

Darwin's interest in variation in animals and plants led him to examine many different organisms, both wild and domestic. However, he was aware that his unusual scientific background meant that he had not developed a his reputation on the basis of detailed scientific study in a particular area.  Therefore, from 1846 to 1854 Darwin focused on barnacle diversity and revolutionised understanding of barnacles, producing the monographs Living Cirripedia that are still relevant today.

 

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Capitulum mitella

 

Darwin's barnacle studies gave him the credibility to pronounce on the origin of species; he found great variation in morphology, and a series of related species with remarkable reproductive adaptation, culminating in the presence of dwarf males. Barnacles laid out an evolutionary narrative before him, and contributed greatly to his qualification and confidence to write with authority on the origin of species by 1859.


PS Rainbow (2011) Charles Darwin and marine biology. Marine Ecology. doi:10.1111/j.1439-0485.2010.00421.x

 

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Charles Darwin is best known as an evolutionary biologist but he also had significant success as a geologist.  His first three scientific books after his account of the voyage of the Beagle explored the geology of coral reefs, volcanic islands and South America: The Structure and Distribution of Coral Reefs (1842); Geological Observations of Volcanic Islands (1844); and Geological Observations on South  America (1846).

Dr Brian Rosen, a Scientific Associate in the NHM Department of Zoology, gave an invited public lecture, hosted by the Bermuda Institute of Ocean Sciences (BIOS) in their ‘Distinguished Lecture Series’ in November 2010, entitled ‘Red or Blue? Darwin's Bermuda Dilemma and his Enduring Subsidence Theory of Coral Reefs’, in which he discussed Darwin's ideas and conclusions.

Darwin's subsidence theory of the origin of coral atolls was based on the idea that the world's ocean floors as a whole were subsiding, and that atolls had developed as coral growth kept pace with sea level on the sinking foundations of former volcanoes. The sheer scale and simplicity of Darwin's idea was reflected in his famous coral reef map, on which he shaded atolls and most other oceanic reefs in blue (inferring subsidence), and most reefs elsewhere in red (inferring uplift or stability).

Darwin's theory was initially acclaimed but over time it seemed too revolutionary for many - alternative ideas such as sea level changes were preferred.  However, by the mid twentieth century, it became clear that the reef deposits of most atolls did indeed extend hundreds of metres beneath their surfaces - far deeper than can be explained by glacial sea level changes alone. 

We know now that atolls do form because islands sink gradually as a  consequence of tectonic plate movement.  While Darwin was correct about  the subsidence, tectonic plate movement and sinking as a reason was not proposed until 1912, althougth this was hotly contested until scientific explanation in the 1950s and 1960s.

Although Darwin did not visit Bermuda, he included it in his coral reef book. Bermuda's reefs - being essentially ring-like in arrangement, and with a central lagoon - are atoll-like, but for other reasons Darwin was equivocal about whether it was a true atoll, so he left it uncoloured on his reef map. In his lecture Brian Rosen attempted to resolve Darwin's dilemma, based on the fact that the sea levels at Bermuda have fluctuated over time.