17.3.2

Evidence for Evolution

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The Evidence for Evolution by Natural Selection

The theory of evolution by natural selection has three main evidence sources:

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Evidence from fossils

  • Fossils are the remains or traces of ancient life.
  • Fossils are found in rocks and have been preserved by natural processes.
  • Fossils show the gradual changes in organisms over vast periods of time.
  • They can help us to see physical similarities in organisms, but not all organisms leave a fossil behind when they die. This means there are big gaps in the fossil record that we have.
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Evidence from DNA

  • Genomes of different species can be sequenced and compared to see how similar they are to each other.
  • Even distantly related organisms share a surprising amount of the same DNA, implying that organisms shared a common ancestor.
  • The more similar the genomes are to each other, the more closely related they are; this often confirms what fossil evidence tells us.
  • In eukaryotes, we can also sequence mitochondrial DNA, which has been used to examine human evolutionary relationships through the maternal line.
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Molecular evidence

  • Molecular evidence includes any evidence from biological molecules, including DNA, but also comparisons of RNA, amino acid sequences, and overall protein structure.
  • Some proteins, like cytochrome c in mitochondria (used in respiration), are highly conserved across organisms. By looking at small changes in highly conserved proteins, we can work out relatedness of different taxa.
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Importance of evidence

  • Sometimes, organisms we think are closely related because of their physical characteristics have more differences in their genome sequence than we might expect.
  • This is why it is important to use a variety of evidence to confirm evolutionary relationships.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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