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Field guide to evolutionary trees

How to build a tree

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The Tree Room : How to build a tree :

True trees

Here, we've seen that tree building depends on which characters are analyzed and the method of construction. Understanding how trees are built helps us make sense of why trees sometimes change when new evidence is considered — for example, why a newly discovered hominin fossil may cause a revision of our branch of the Tree of Life. Science is an ongoing process, and new evidence or new insights into an analysis sometimes prompts scientists to reevaluate their hypotheses. Phylogenetic hypotheses are no different. If new evidence relevant to an evolutionary tree is uncovered, biologists must figure out whether this evidence supports the current understanding of evolutionary relationships in the group or a different one. Changing trees simply reflect a better informed understanding of the Tree of Life.

This all means that trees are not set in stone — and yet neither do they change all the time. On the contrary, most of the relationships depicted in evolutionary trees that we encounter in modern articles and textbooks are so well supported (and continue to be supported by newly discovered evidence) that few of the connections represented on them are likely to change. In addition, as we gather more clues from new genetic data and deploy more powerful techniques for analyzing these data, we can expect some relationships that scientists are currently debating — like the relationships among early animal lineages — to be clarified. After all, all of these efforts to gather a wide range of evidence and apply different techniques aim to converge on the same tree — the tree that represents the true history of life.

animal tree
One hypothesis regarding the relationships among early animal lineages. Additional research is likely to reveal which of the several hypotheses regarding these relationships is most accurate.

To learn even more about tree building, visit these Understanding Evolution resources:

Animal tree adapted from Nosenko, T., F. Schreiber, M. Adamska, M. Adamski, M. Eitel, J. Hammel, … and G. Wörheide. 2013. Deep metazoan phylogeny: When different genes tell different stories. Molecular Phylogenetics and Evolution 67:223-233.

Ostrich photo by Nevit Dilmen (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Moon jellyfish (Cnidaria) photo by Alexander Vasenin (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Ctenophore photo by Kevin Raskoff (Mertensia on oceanexplorer.noaa.gov) [Public domain], via Wikimedia Commons

Placozoa photo by Bernd Schierwater [CC BY 4.0], via Wikimedia Commons

Porifera photo by Nhobgood (talk) Nick Hobgood (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Choanoflagellata photo by Dhzanette (http://en.wikipedia.org/wiki/Choanoflagellate) [Public domain], via Wikimedia Commons

How to build a tree
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Evo examples
Feeling lost? Review tree basics with the primer.