Explaining evolution 9 – Darwin’s Finches


Blog 9 in our GCSE Science series on evolution looks at Darwin’s Finches.

Explaining evolution 9 – Darwin’s finches

The AQA GCSE Combined Science syllabus poses the question: ‘How do new species of plants and animals develop?’  The finches of the Galapagos Islands (or Darwin’s finches) are a good example of how evolution explains the development of a range of related species.

During his voyage around the world during the 1830’s Charles Darwin collected many natural specimens including some birds from the Galapagos Islands.  These islands are volcanic and are relatively new land masses, having risen out of the sea.  They are approximately 970 km from mainland South America, so organisms on the island have been isolated from most land-based animals.

Darwin collected a range of (what he thought were) unrelated birds from the islands. These birds had different body sizes and different beak sizes and shapes, but, on closer examination by bird experts, were all found to be different species of the finch family and distantly related to those found on mainland South America.

Darwin came to the conclusion that seed-eating finches had flown to the Galapagos Islands from mainland South America and flourished because there was sufficient seed and nuts. Random mutations produced some birds with a smaller body size and beaks. These birds also survived because they were able to locate and eat other types of smaller food (e.g. insects in wood bark and under stones) that was not easily available to the larger seed-eating birds.  If there was an abundance of seeds and fruit the larger seed-eating finches may not have required the insect food.

These smaller birds survived and passed on their characteristics to their offspring. Because of the range and locations of available insect food even smaller finches survived, some with more pointed beaks, and again passed on their characteristics to their offspring.

Over many thousands of generations new species of smaller finches with slender, thin, insect-eating beaks evolved from the original large finches with strong, thick, seed-eating beaks.  The species of smaller finches varied from island to island as each group developed their own characteristics.

Observations of ‘Darwin’s finches’ support the following points in the AQA GCSE Combined Science syllabus:

  • individual organisms within a particular species may show a wide range of variation because of differences in their genes;
  • individuals with characteristics most suited to the environment are more likely to survive to breed successfully.

The first point refers to ‘genes’, an area of science not then available to Darwin and his colleagues, but which now provides a secure foundation for evolution.  The next blog in the series, Explaining evolution 10 – Recent evidence to support evolution, looks at this in more detail.

John Roach

Tutor

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