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Common ancestry and evolutionary trees

Review your understanding of common ancestry and evolutionary trees in this free article aligned to NGSS standards.

Key points

  • Each modern species has a series of ancestral species stretching back through time. This series of ancestors is a species’ evolutionary lineage.
  • A common ancestor is an ancestral group of organisms that is shared by multiple lineages. For example, an early mammal species, which existed sometime in the distant past, is a common ancestor of whales, cats, humans, and all other modern mammals.
  • An evolutionary tree models the relationships between different lineages and their common ancestors.
  • Evolutionary trees have a branching pattern. The tips of the branches represent modern groups of organisms. The branch points, or places where the branches split, represent common ancestors that existed in the past.
  • Species that share a common ancestor in the more recent past are more closely related. Species that share a common ancestor in the more distant past are less closely related.
A diagonal line starts at the bottom of a diagram and travels up and to the right. It is labeled species C at the top. Two diagonal lines branch off of this main line and travel up and to the left until they reach the same level as the top of the main line. The shorter of these lines branches off near the top and is labeled species B. A slightly longer line branches off near the bottom and is labeled species A. The point where the shorter line branches off from the main line is labeled common ancestor of species B and C. The point where the longer line branches off from the main line is labeled common ancestor of species A, B, and C.
An evolutionary tree showing the relationships between three species. The labeled branch points represent common ancestors. Image created with Biorender.com.

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