7.2 Evidence for Evolution
Notes
Many independent lines of evidence support evolution.
- Fossils show organisms changed over time; deeper rock layers usually hold older fossils.
- Homologous structures have the same basic bone structure but different uses (human arm, whale flipper, bat wing). They point to a common ancestor.
- Analogous structures have the same use but different structure (bird wing and insect wing); they do not show close relationship.
- Vestigial structures are reduced parts with little or no use (whale hip bones).
- Embryology: early embryos of vertebrates look similar.
- DNA and protein comparisons: more similar sequences mean a more recent common ancestor.
Practice
A human arm, a cat leg and a whale flipper have the same set of bones. These are:
Same structure with different functions shows common ancestry.
Species A's hemoglobin differs from humans' by 1 amino acid, species B's by 12, and species C's by 45. Which species is most closely related to humans?
Fewer differences means a more recent common ancestor.
Some snakes have tiny leftover hip bones that they do not use for walking. These are:
Vestigial structures are reduced remnants from ancestors.
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