7.9 Phylogeny

Describe the types of evidence that can be used to infer an evolutionary relationship.

• Phylogenetic trees and cladograms show hypothetical evolutionary relationships among lineages that can be tested.
• Phylogenetic trees show the amount of change over time calibrated by fossils or a molecular clock, whereas cladograms do not show time scale or the evolutionary difference between groups.
• T raits that are either gained or lost during evolution can be used to construct phylogenetic trees and cladograms. The out-group represents the lineage that is least closely related to the remainder of the organisms in the phylogenetic tree or cladogram.
  • i. Shared derived characters can be present in more than one lineage and indicat e common ancestry. These are informative for the construction of phylogenetic trees and cladograms.
  • ii. Molecular data typically provide more accurat e and reliable evidence than morphological traits in the construction of phylogenetic trees or cladograms.

Explain how phylogenetic trees and cladograms can be used to infer evolutionary relatedness.

• Phylogenetic trees and cladograms can be used to illustrate speciation that has occurred. The nodes on a tree represent the most recent common ancestor of any two groups or lineages.
• Phylogenetic trees and cladograms can be constructed from morphological similarities of living or fossil species and from DNA and protein sequence similarities.
• Phylogenetic trees and cladograms represent hypotheses that are constantly being revised based on evidence.