Understanding Evolution

The Tree Room :

How to build a tree
by the Understanding Evolution team

Evolutionary trees (also called phylogenetic trees) represent the relationships among different lineages, but how do we know what these relationships are in the first place? Are evolutionary trees set in stone? Are they based on facts that are simply obvious to scientists? On the contrary, biologists have to put a lot of scientific study into figuring out how different species and groups of species are related to one another. They make detailed anatomical observations and measurements, travel all over the world to collect DNA samples, and run programs on computers that may take days or weeks to finish — all for the purpose of better understanding the Tree of Life. Even very broad patterns — such as the now well-established idea that robins are more closely related to Tyrannosaurus than they are to mice — may be the result of years of scientific study and debate.

Life collage
Figuring out how such diverse organisms are related to one another evolutionarily is the subject of much scientific study.

Most learners don't need a complete understanding of how scientists construct phylogenetic trees, but knowing even the basics of how trees are built will help anyone get more out of the trees they see. In this module, we'll review those basics:

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French Angelfish by Eugene Weber © California Academy of Sciences; Yellow Fritillary, Chalk White Nudibranch, and Galapagos Tortoise by Gerald and Buff Corsi © California Academy of Sciences; Bacteria (Escherichia coli) from Rocky Mountain Laboratories, NIAID, NIH; Black Widow Spider by George W. Robinson © California Academy of Sciences; Deer Fern © Br. Alfred Brousseau, Saint Mary's College; Honey Mushroom by Dr. Robert Thomas and Dorothy B. Orr © California Academy of Sciences; Whitebark Pine by Charles Webber © California Academy of Sciences; Farmer by Neil Palmer, International Center for Tropical Agriculture (CC BY-SA 2.0)

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