13 Phylogenetic Trees: Modeling Evolution

Andrea Bierema

 

Learning Objectives

Students will be able to:

  • Provide accurate explanations of a phylogenetic tree, which is a scientific model that explains how species are evolutionarily related to each other.
  • Convert relevant information into a phylogenetic tree.
  • Identify common ancestors on a phylogenetic tree.
  • Label shared derived characteristics on a phylogenetic tree.

The History of Life: Looking at the Patterns

The central ideas of evolution are that life has a history—it has changed over time—and that different species share common ancestors.

Here, you can explore how evolutionary change and evolutionary relationships are represented in “family trees,” how these trees are constructed, and how this knowledge affects biological classification. You will also find a timeline of evolutionary history and information on some specific events in the history of life: human evolution and the origin of life.

The Family Tree

The process of evolution produces a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships.

By studying inherited species’ characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent them on a “family tree,” called a phylogeny. The phylogeny you see below represents the basic relationships that tie all life on Earth together.

The Three Domains

This tree, like all phylogenetic trees, is a hypothesis about the relationships among organisms. It illustrates the idea that all of life is related and can be divided into three major clades, often referred to as the three domains: Archaea, Bacteria, and Eukaryota. We can zoom in on particular branches of the tree to explore the phylogeny of particular lineages, such as Animalia (outlined in red). Then we can zoom in even further to examine some of the major lineages within Vertebrata. Just click the button in the center of the image below.

The tree is supported by many lines of evidence, but it is probably not flawless. Scientists constantly reevaluate hypotheses and compare them to new evidence. As scientists gather even more data, they may revise these particular hypotheses, rearranging some of the branches on the tree. For example, evidence discovered in the last 50 years suggests that birds are dinosaurs, which required adjustment to several “vertebrate twigs.”

Understanding Phylogenies

The following diagram describes the different components of phylogenetic trees. Click on the Information tab in each box to learn more!

For additional help on understanding phylogenies, see Learn.Genetic’s “Tree Diagrams” video and “Tree Diagrams” interactive.

 

Exercise

Let’s see what you learned!

You can also go back to the HHMI Biointeractive’s Lizard Evolution lab. Once you launch the interactive, click on the module tab to the left, and select “Module 2: Phylogeny.”

Want even more practice? Try Nova Lab’s The Evolution Lab!

Attribution

This chapter is a modified derivative of Understanding Evolution. 2020. University of California Museum of Paleontology. 22 August 2008 <http://evolution.berkeley.edu/>.