1. Lesson Module: Classification of Organisms
Tree of Life
Lesson Module: Classification of Organisms

2. You are here
Let’s take a quick tour of this tree. We are here, closely related to other vertebrates (in this limited sample of species, we are grouped with the three other mammal species in the sample).
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(see Science 300: )

3. The cotton in your shirt came from here You are here
The cotton fibers in your shirt (if you are wearing cotton) came from a plant that is located over in this part of the tree.
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4. What if, a billion years ago…
The cotton in your
shirt came from here
You are here
What if, a billion years ago…
It is fun to consider that about 1 billion years ago, a species underwent a speciation event. At that time, the two descendant species that resulted from that speciation event would have been very similar, as all species are soon after they split. If anyone had been around at the time to think about it (remember, this was nearly a billion years before humans walked the Earth), they might have wondered if it was actually very important for the future of the Earth for both of these similar species to survive. But, one billion years later, the descendants of one of those two species include all the green plants, and the descendants of the other species include humans, mushrooms, and of course all the other great diversity of animals and fungi (yes, we are more closely related to mushrooms than we are to plants). Ponder this point the next time that someone wonders why we need to protect biological diversity.
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5. The cotton in your shirt came from here You are here The E.coli
To finish our quick tour of the Tree of Life, we could also locate the bacteria that inhabit your gut…
The E.coli
in your gut
is here
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6. The cotton in your shirt came from here You are here The E.coli
…as well as the fungus that is on your foot. For fun, you might trace the lineages back from the fungus, ourselves, the plant, and the bacterium to convince yourself that our closest relative among these four is the fungus!
This tree is hard to see in any detail in a PowerPoint presentation. If you would like to have a wall-sized version of this poster, you can download the file from and print a poster-sized version. It is best seen when printed at least 54” wide (this can be done on several sheets if necessary).
The E.coli
in your gut
is here
The fungus
on your foot
is here
Download wall poster from:
(see Science 300: )

7. To AmphibiaTree and beyond…
Now biologists are working to fill out the tips of the Tree of Life. For instance, one group of biologists (including biologists at the University of Texas) is working on the Amphibian Tree of Life project, which aims to build a phylogenetic tree of all known amphibians. These databases are critical for many applications, including the development of rapid methods of identification, such as the Biocorder.
Download wall poster from:
(see Science 300: )