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vert bar DARWIN DAY 12th February 2006

Charles Darwin and the theory of Natural Selection

The notion of evolution via genetic variation and natural selection, proposed by Charles Darwin, has become the central organizing principle in biology. Since the 1990s his birthday has been celebrated by public events to mark his outstanding contribution to science. The publication of his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life in 1859 laid the foundations for modern evolutionary thought.

No sooner had his book been published, than Darwin retreated from the public debate thus created and began putting his theories into practice through detailed studies on the biology of Carnivorous plants and the pollination of Orchids at his home in Kent, Downe House. In 1862, Charles Darwin published a book on the evolutionary biology of orchids, On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects. His practical work on British orchids allowed him to look at tropical orchids with greater understanding.

Charles Darwin and the Madagascan Comet Orchid
He discovered, for example, that the combination of a star-shaped white flower and a long narrow nectar spur indicated that the flower was moth-pollinated. Thus when examining the blooms of the Madagascan Comet orchid (Angraecum sesquipedale, right), which has a flower spur nearly one foot long (sesquipedale is Latin for One and a half foot – some say it refers to the flower stalk, others that it is an exaggerated reference to the spur!), he stated that “… in Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches !

Alfred Russel Wallace (one of Charles Darwin's greatest admirers and independent formulator of the theory of Natural Selection) came to the same conclusion, and went further as to say “That such a moth exists in Madagascar may be safely predicted; and naturalists who visit that island should search for it with as much confidence as astronomers searched for the planet Neptune” (Wallace 1867, 1871).

The supposed pollinator of Angraecum sesquipedale, a Sphinx moth (Xanthopan morgani praedicta) with a proboscis (tongue) 25 cm long was indeed found and described 41 years after Darwin's prediction. However, whilst the prediction still seems a near certainty, the actual incidence of this moth pollinating the Madagascan Comet Orchid has yet to be witnessed.