The Galapagos Islands
How it Works
There are four main steps in the process of Natural Selection:
- There is a population that has variation.
- Some variations help with survival and the individuals without that trail will die. The individuals with a favourable trait will survive and reproduce.
- The genes for the favourable trait are passed down to the offspring.
- In the next generation, there will be a higher number of individuals with the favourable trait.
Natural selection works only if the trait is genetic and can be passed down through generations from parents to offspring.
Who Came Up With the Theory
"I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection."
Charles Darwin, The Origin of Species
Darwin studied many species and theorised about evolution. Darwin found that natural selection is one of the main mechanisms for evolution, He used the theory of natural selection and his study of different species to support his theory of evolution.
What Are They
Genus and Species:
- Large Cactus Finch (Geospiza conirostris)
- Sharp-beaked Ground Finch (Geospiza difficilis)
- Vampire Finch (Geospiza difficilis septentrionalis)
- Medium Ground Finch (Geospiza fortis)
- Small Ground Finch (Geospiza fuliginosa)
- Large Ground Finch (Geospiza magnirostris)
- Darwin's Large Ground Finch (Geospiza magnirostris magnirostris) – possibly extinct (1957?)
- Common Cactus Finch (Geospiza scandens)
- Large Tree Finch (Camarhynchus psittacula)
- Medium Tree Finch (Camarhynchus pauper)
- Small Tree Finch (Camarhynchus parvulus)
- Woodpecker Finch (Camarhynchus pallidus) – sometimes separated in Cactospiza
- Mangrove Finch (Camarhynchus heliobates)
- Green Warbler-Finch (Certhidea olivacea)
- Grey Warbler-Finch (Certhidea fusca)
- Cocos Finch (Pinaroloxias inornata)
- Vegetarian Finch (Platyspiza crassirostris)
"Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends... Unfortunately most of the specimens of the finch tribe were mingled together; but I have strong reasons to suspect that some of the species of the sub-group Geospiza are confined to separate islands. If the different islands have their representatives of Geospiza, it may help to explain the singularly large number of the species of this sub-group in this one small archipelago, and as a probable consequence of their numbers, the perfectly graduated series in the size of their beaks." (pp403-420)
Darwin, Journal of Researches into the Natural History and Geology of the countries visited during the voyage round the world of H.M.S. Beagle, revised edition, Henry Colburn 1845.
Darwin assumed correctly of course - the different types of finch with different beak shapes and sizes came from separate islands in the Galapagos. Although Darwin didn't have enough data to use the finches as examples of natural selection in his book, they played a significant role in his formulation of the theory.
Different Beak Shape
Different Beak Size
The finches with beaks that are shaped to eat seeds still compete for resources within their species.
During dry years, there is more availability of large seeds so the finches with slightly larger beaks are able to collect and crack through the shells to eat the seeds. They thrive in seasons of drought and have more offspring than the finches with smaller beaks. The ones with smaller beaks are unable to collect and eat the larger seeds and can't survive. In the next generation there will be more finches with larger beaks.
It is the converse for wet years - the finches with smaller beaks are able to collect more food and survive to pass on the gene of smaller beaks to the next generation.
Natural Selection in the Galapagos Video
As shown from 10:50-12:04 in the video above, finches on the same island with very similar characteristics still continue to compete for resources and the birds with slight variations that help them to collect enough food for survival will pass those variations on to their offspring but those with variations that have a negative effect on how well they are able to compete for resources in the environment, will not survive and therefore will not be able to pass that characteristic on the their offspring.
Why The Finches Are Important
The finches can be used as a simple model to demonstrate and explain Natural Selection.
By Brittany Lewis