1.2 What Is Phylogeny?

Phylogeny is the study of evolutionary relationships between organisms and how different species are connected through common ancestry. Scientists use phylogeny to determine how closely related organisms are by comparing shared characteristics, such as anatomical features, developmental patterns, and genetic information. Species that share more traits inherited from a common ancestor are considered more closely related.

Phylogenetic trees are visual models that represent these relationships. They are not fixed diagrams, but scientific hypotheses based on the best available evidence at a given time. As new data become available—such as fossil discoveries or advances in DNA analysis—phylogenetic trees can be revised and improved. This makes phylogeny a dynamic and evidence-based field that reflects how scientific understanding evolves over time.

Understanding phylogeny helps scientists explain biodiversity, trace the origins of species, and identify evolutionary patterns. It also teaches an important scientific principle: biological knowledge is built through comparison, evidence, and continuous refinement, rather than absolute or unchanging answers.

Below are examples of phylogeny:

  1. Tree of life of amniotes that includes reptiles, birds, and mammals. All these classes of vertebrates evolved from the same ancestral form of the stem reptiles at the bottom of the tree (Sourse: https://www.researchgate.net/figure/Tree-of-life-of-amniotes-that-includes-reptiles-birds-and-mammals-All-these-classes-of_fig2_323780429) 
    Tree of life of amniotes that includes reptiles, birds, and mammals. All these classes of vertebrates evolved from the same ancestral form of the stem reptiles at the bottom of the tree. 
  2. Tree Of Life Human Evolution Biology Species Classification. Tree of life of all living beings. Phylogenetic tree of biological science with trunk orders/suborders and branches related life forms. Classification from simple organisms to modern humans. (Source: https://www.dreamstime.com/tree-life-human-evolution-biology-species-classification-tree-life-all-living-beings-phylogenetic-tree-biological-image131543711)
     
  3. Phylogenetic history of the Hominidaedliving apes and people (Source: https://www.researchgate.net/figure/Phylogenetic-history-of-the-Hominidaedliving-apes-and-people-Dates-are-based-on-genomic_fig1_317314464)
    Phylogenetic history of the Hominidaedliving apes and people. Dates are based on genomic analysis and are approximate. Source: NOVA Education, Classroom Activity, Ó 2010 WGBH Educational Foundation. Available at: http://www.pbs.org/wgbh/nova/education/activities/3416_id.html (accessed 08.01.16). Used with permission.