Short essay – Evolution and Natural Selection



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SHORT ESSAY – Evolution and Natural Selection
A species of birds lives on an island. The thickness of the birds' beaks varies within the population. The birds feed mainly on seeds from plants. Birds with thinner beaks can eat only small seeds. Only birds with thicker beaks can crush and eat large seeds. There are many small seeds during years with more rain. During dry years, there are very few small seeds and many large seeds. The large seeds are harder to crush than small seeds.

The graph below shows the average beak thickness in the bird population from 1979 to 1985: 1980 and 1982 were dry years; 1984 was a wet year; 1979, 1981, 1983, and 1985 received normal rainfall.




  • Explain why the average beak thickness changed between wet and dry years.

  • Explain how beak thickness would have changed during the next ten years, 1986 to 1996, if these years were wet years.

  • Name and explain the process that led to this change.


SHORT ESSAY – Evolution and Natural Selection
A species of birds lives on an island. The thickness of the birds' beaks varies within the population. The birds feed mainly on seeds from plants. Birds with thinner beaks can eat only small seeds. Only birds with thicker beaks can crush and eat large seeds. There are many small seeds during years with more rain. During dry years, there are very few small seeds and many large seeds. The large seeds are harder to crush than small seeds.

The graph below shows the average beak thickness in the bird population from 1979 to 1985: 1980 and 1982 were dry years; 1984 was a wet year; 1979, 1981, 1983, and 1985 received normal rainfall.




  • Explain why the average beak thickness changed between wet and dry years.

  • Explain how beak thickness would have changed during the next ten years, 1986 to 1996, if these years were wet years.

  • Name and explain the process that led to this change.


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