Geospizini
A group of finches exemplifying adaptive radiation in beak form.
Geospizini, also known as Darwin's finches or Galápagos finches, are a group of about 18 species of passerine birds classified as the tribe Geospizini (or subfamily Geospizinae). They are a classic example of adaptive radiation, noted for remarkable diversity in beak form and function, and are found only on the Galápagos Islands except for the Cocos finch from Cocos Island. They belong to the tanager family and are not closely related to true finches; their closest known relative is the South American dull-coloured grassquit (Asemospiza obscura).
- common_name
- Darwin's finches
- scientific_classification
- Tribe Geospizini (or subfamily Geospizinae)
- number_of_species
- about 18
- size_range
- 10 to 20 cm (4 to 8 in)
- weight_range
- 8 to 38 grams (0.3 to 1.3 oz)
- distribution
- Galápagos Islands and Cocos Island
- first_collected
- Second voyage of HMS Beagle, with Charles Darwin on board
Lore & Background
The birds were first collected during the second voyage of HMS Beagle when Charles Darwin visited the Galápagos Islands as a gentleman naturalist. Darwin was unaware of their significance at the time, concentrating mainly on geology and leaving bird shooting to his servant Syms Covington. After the voyage, Darwin presented the finches to the Zoological Society of London on 4 January 1837, and they were given to ornithologist John Gould for identification. On 10 January 1837, Gould reported that the birds Darwin had thought were blackbirds, 'gross-beaks' and finches were actually 'a series of ground Finches which are so peculiar [as to form] an entirely new group, containing 12 species.'
Reader's Guide
Darwin's finches are significant as a classic example of adaptive radiation, illustrating how a single ancestral finch species that arrived on the Galápagos Islands more than a million years ago diversified into multiple species with different beak forms adapted to various food sources. Their role in the development of Darwin's theory of evolution by natural selection is notable: after Gould identified the finches as distinct species, Darwin realized that if finch species were confined to individual islands, this would help account for the number of species on the islands. In the second edition of The Voyage of the Beagle (1845), Darwin wrote that 'one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.' The finches remain a key example in evolutionary biology, demonstrating how geographical isolation and ecological pressures can drive speciation. Their beaks show a nearly perfect gradation in size and shape, from that of a large gros-beak to that of a warbler, as Darwin noted.
Did You Know?
- The term 'Darwin's finches' was first applied by Percy Lowe in 1936 and popularised by David Lack in 1947.
- The closest known relative of the Galápagos finches is the South American dull-coloured grassquit (Asemospiza obscura).
- Darwin was unaware of the significance of the finches during the voyage and mostly left bird shooting to his servant Syms Covington.
- John Gould identified 12 species of ground finches from Darwin's specimens, reporting them on 10 January 1837.
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