Download Darwin`s Finches

Darwin’s Finches
The variety of finches of the Galapagos Islands is a result of natural selection and speciation.
The finches are split into 2 large groups – ground finches and tree finches. The species that live on the
ground each eat different types of seeds or cactus. The tree finches each eat different types of bugs. In each
species of bird the beak has become modified for its specific diet.
When Darwin visited the Galapagos Islands he concluded (and his conclusions are backed by years of
careful research by others) that the different species of finches were all descended from the same common
ancestor. Long ago, about 10,000 years ago, the volcanic islands were colonized by South American finches
that probably were blown out to sea by a storm. Apparently, conditions on the islands were favorable, and the
finches flourished.
Their descendants eventually populated all the islands by occasional island hopping. What followed
was speciation. In this example of speciation, many species arose from a common ancestor that was
introduced to a new environment with new opportunities and new problems for the species to survive.
The original ground finches from South America had the islands to themselves, as far as they were
concerned. There was a great variety of food. They were already well adapted for searching for small seeds
on the ground, but there were other plentiful untapped food resources – food not ordinarily eaten by finches.
However, the growing populations of finches eventually started to use up the available supply of small
seeds. Thus, natural selection began to favor birds that could also cope with larger seeds and with other food
sources. In time, the size and shape of the bird’s beaks changed through the process of natural selection as
each population began to adapt more closely to the different kinds of food found on each island.
As differences in lifestyles and specialization became magnified among diverging populations,
competition for food would have been reduced. After thousands of years of divergence on the Galapagos
Islands the different finch species were unable to interbreed. Clearly, speciation (the formation of new species)
had occurred.
Family Tree of Darwin’s Finches
Common Ancestor
(from South America)
DARWINS FINCHES
ANSWER IN YOUR NOTEBOOK IN COMPLETE SENTENCES
1. What are the 2 main groups of finches Darwin observed? What does each eat?
2. How did the finches probably end up on the Galapagos Islands when they were on the continent of South
America?
3. What was different on the islands that caused the beaks to change? How long did this change take?
4. What is speciation?
5. Look at the Family tree of Darwins Finches. List the different groups of finches.
6. What did the ancestral finch eat?
7. Explain how these finches are an example of natural selection.