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Interpreting evolutionary trees and relatedness

Inheritance, variation and evolution • Classification of living organisms

Key concepts

What you'll likely be quizzed about

  • An evolutionary tree consists of lines that represent lineages and nodes that signify common ancestors from which multiple lineages diverge.
  • Each node indicates an ancestral population, and species that descend from the same node share traits inherited from that ancestor.
  • The arrangement of branches displays their relatedness; species that share a node nearer to the tips are more closely related.
  • Examples often show vertebrate and primate trees that visually clarify relatedness through branching order.

Flashcards

Test your knowledge with interactive flashcards

Role of fossils in tree building

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Fossils provide direct evidence of historical organisms and help contextualize divergence events, although gaps in records can limit insights.

Key notes

Important points to keep in mind

Nodes indicate common ancestors and shared ancestry.

Relatedness is based on shared ancestry, not superficial similarity.

Branch order reveals divergence sequence; closer nodes imply closer relationships.

Branch length may reflect genetic change or time; always refer to the legend.

Polytomies signify uncertainty regarding divergence order.

Molecular data often refine relationships inferred from morphology.

Fossil gaps and horizontal gene transfer may diminish confidence in certain trees.

Clarify assumptions and indicate tree rooting when discussing relationships.

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