The Tree of Life
This Tree of Life diagram is based primarily on the evolutionary relationships so wonderfully related in Dr. Richard Dawkins’ The Ancestor's Tale, and timetree.org. The smallest branches are purely illustrative. They are intended to suggest the effect of mass extinctions on diversity, and changes in diversity through time. This diagram is NOT intended to be a scholarly reference tool! It is intended to be an easy-to-understand illustration of the core evolution principle; we are related not only to every living thing, but also to everything that has ever lived on Earth.
Educational posters of this Tree of Life are available from our shop. We also make custom posters of the Tree of Life using a design and size of your choice. Contact us at https://www.evogeneao.com/contact-us
Go to our page for teachers to see how the Tree of Life is used in the classroom to teach evolution.
Distortions and Limitations
In order to make the Tree of Life uncluttered and easy to understand, a number of distortions have been purposefully built in.
First, and most importantly, this Tree of Life is drawn from the human, mammalian point of view. That is why humankind, instead of some other organism, occupies a branch tip at the end of the tree, and why our vertebrate cousins (animals with a backbone) occupy a large part of the tree. This falsely suggests that humans are the ultimate goal of evolution. In fact, if that asteroid or comet that hit the earth 66 million years ago and helped wipe out the dinosaurs, had instead missed the earth, there might not be a dominant, tool-using, space-faring species on earth. Or if one evolved, it might be a dinosaur, not a mammal.
Second, the world of bacteria holds far more genetic diversity, and accounts for a vastly larger proportion of biomass than animals do, yet bacteria occupy only a relatively small portion of the tree. Trees of Life drawn from the bacterial point of view look very different: on these diagrams, the whole world of animals and plants occupy only a tiny part of the tree.
Third, this tree of life diagram suggests life steadily increased in diversity through time, such that the greatest diversity appears to exist at the present time. This is not at all the case in life history and only appears that way in this diagram because, for space reasons, only a few of the main branches of life that have gone extinct are shown. The evidence suggests that many more branches have gone extinct than exist today. One estimate concludes that 99% of species that have ever existed on earth are now extinct. If the diagram could be drawn to really reflect life history, the greatest diversity in major body plans would probably appear early in the Cambrian Period, around 530 million years ago. Only a few major body plans survived the Cambrian, but these few have evolved into the diversity we have today.
Fourth, for space reasons many minor branches of life have not been included or labeled on the Tree of Life diagram. Also, the diagram suggests a specific time of common ancestry where branches join, but DNA data only suggest a broad time window in which the common ancestor lived.
Fifth, this Tree of Life diagram breaks out Birds as a separate major branch, although the scientific consensus now is that birds are a branch of theropod dinosaurs that survived the mass extinction 66 million years ago. The branch could be labeled "Avian Dinosaurs," but to make the diagram easier for folks to follow, the more familiar designation "Birds" has been retained. Follow the Bird branch back in time to its connection to the rest of the dinosaurs, and the intimate connection between birds and dinosaurs is easily seen.
Sixth, most current study on the beginning of life on earth proposes that 1) Bacteria and Archaea probably evolved from a common ancestor, either a non-living proto-cell, or something alive but more primitive than either, but now long gone, and 2) that Eukaryotes evolved from Archaea. Everything alive on earth today can trace ancestry back to that common ancestor between Bacteria and Archaea, which is known as LUCA (Last Universal Common Ancestor). Hug, et al., 2016 (Nature Microbiology 1:16048)
In order to keep the diagram simple and easy to understand for beginning students, the Tree of Life diagram shows a simple, traditional progression from Bacteria to Archaea to Eukaryotes.
Seventh, for a very recent common ancestor, we can reasonably be sure it didn't look too different from a modern descendant, and fossil data is often available to guide the illustrations of them that we've created for our Tree of Life Explorer interactive web feature
But science has only an approximate idea of what really ancient common ancestors may have looked like. On the Tree of Life Explorer we've made highly speculative illustrations of these ancient ones, and we've assumed in most cases that they looked like a modern example of the next oldest branch on our Tree of Life. This assumes that little evolutionary change has taken place in the form of that organism, which is a big, and probably wrong assumption. But we decided to follow that admittedly flawed protocol, rather than just replace those common ancestor illustrations with a big question mark. Teachers are encouraged to explore this issue with their classes, as it is a great way to dive deeper into the study of evolution.
Teachers are encouraged to examine issues raised in the Distortions and Limitations text about the Tree of Life diagram, for those students able to dive a bit deeper into evolution.
How to Use the Tree of Life
The geologic time scale on the Tree of Life begins at the center bottom, at Earth's birth, more than four thousand million (4 billion) years ago. As you move away from this center point toward the outer margin of the tree, geologic time gets younger and younger, until at the outer curved edge of the tree you arrive at the present day. Times on the geologic time scale are shown at the base of the diagram in millions of years before present. These are traced through the tree of life along curved, dashed time lines. All points on a curved, dashed time line are of the same age. For example; any point on the dashed time line labeled '1000' represents a time 1000 million years (that's equal to one billion years) in the past. Similarly, any point on the outer margin of the tree represents time today. Any point on the tree of life can be placed in geologic time by using these curved time lines. Click the diagram below to enlarge.
Biological evolution proposes that all living things, including humans, have a common ancestor with any other living thing. On the Tree of Life you can explore when in the distant past these common ancestors lived. For example, explore when the common ancestor between fish and humans lived by using the partial Tree of Life diagram below. Begin by tracing the human branch back through time along the yellow guide lines. Start at the point on the outer margin of the tree (in other words, today) that is labeled 'humans'. Follow it back in time down the dark brown mammal branch to where it joins the light brown mammal-like reptile branch, then continue back to the point where you meet the bright blue fish branch. This point on the Tree of Life represents the common ancestor between humans and fish (in this case, salmon), and, by using the time scale, you can see that this creature lived roughly 430 million years ago. The time of a common ancestor between any two of life's branches, large or small, on the Tree of Life can be found in the same way.
Want to try another one? Follow the Reptile branch back in time to the point where it meets the Amphibian branch. Compare this to the curved time lines and you can see that this meeting point, which represents the time when the common ancestor between amphibians and reptiles lived, was about 355 million years ago. Each of the major branches on the Tree of Life are color coded to make them easier to distinguish from neighboring branches.
Our Understanding Will Evolve
As our understanding of life's history improves (by further discoveries in the fossil record and genetics), some of the branching relationships and times of common ancestors depicted on this tree of life will inevitably become outdated.
Our Tree of Life in Other Languages
Visitors and customers of Evogeneao come from all over our planet. Folks in Japan, Australia, Thailand, Sweden, Germany, United Kingdom, France, Belgium, Turkey, The Netherlands, Spain, Ukraine, Argentina, Mexico, India and many other wonderful places have voiced their support for evolution, and the fact that all Life on Earth is One Big Extended Family. In this spirit, Martha Ruszkowski translated the Evogeneao Tree of Life page into Ukrainian! If any Evogeneao visitors feel moved to do a translation of the tree of life page, other parts of Evogeneao, or just the diagram, into their own language, we would love to include it in this section of the website and acknowledge your authorship and web presence.
Dr. Emanuele Serrelli from University of Milano Bicocca used Evogeneao in a science fair in Milan, Italy in fall of 2013. We also donated a box of Evogenao tee shirts for the event, and they were a big hit! These are some of the exhibits Dr. Serrelli created to explain evolution the Evogeneao way.