Evolution, Natural Selection, and Speciation

00:00 16 marks

9. (a) Explain how evolution occurs through natural selection. [7]
(b) Outline the evidence for evolution provided by homologous structures. [4]
(c) Describe the concept of a species, including challenges in its definition. [4]

Part a

11 minutes 7 marks

Question

Explain how evolution occurs through natural selection. [7]

Hint Hint

Hint

Outline the key steps: variation, overproduction, competition, differential survival/reproduction, inheritance, change over time.

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Complete Answer

Evolution by natural selection involves variation within a population, overproduction leading to competition, differential survival and reproduction of better-adapted individuals, inheritance of advantageous traits, and a resulting increase in the frequency of these traits over generations.

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Part b

6 minutes 4 marks

Question

Outline the evidence for evolution provided by homologous structures. [4]

Hint Hint

Hint

Define homologous structures, relate them to common ancestry, and give an example like the pentadactyl limb.

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Homologous structures are structures with a similar underlying anatomy due to shared ancestry, but potentially different functions (e.g., pentadactyl limb). This similarity in basic form, despite functional divergence resulting from adaptation to different environments (adaptive radiation), supports evolution from a common ancestor.

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Part c

6 minutes 4 marks

Question

Describe the concept of a species, including challenges in its definition. [4]

Hint Hint

Hint

Define the biological species concept (interbreeding, fertile offspring) and list situations where it doesn’t apply well.

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A species is often defined by the Biological Species Concept as a group of organisms that can interbreed naturally to produce fertile offspring. Challenges to this definition include its inapplicability to asexually reproducing organisms, extinct organisms known only from fossils, geographically isolated populations, organisms forming ring species, and cases where distinct species hybridize.

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