Since Darwin first sketched an evolutionary Tree of Life, many people have created trees that attempt to show how organisms are related to one another. The scientific name for the Tree of Life is “phylogeny.”
As new data become available, these phylogenies have evolved to reflect our growing understanding of biological evolution.
The most recent data suggests that the Tree of Life is really more of a Web of Life. Because of horizontal gene transfer, DNA can flow laterally, between species, as well as flowing vertically, from parent to child. In some organisms, up to two thirds of the genome is transfered laterally, between distantly related organisms. In addition to challenging our understanding of the Tree of Life and evolution, horizontal gene transfer challenges the idea of species.
Web of Life
Ford Doolittle’s image of the Web of Life forever changed the way we look at the Tree of Life. He presents overwhelming data showing the importance of horizontal gene transfer in evolution. In the past, it was observed that DNA was transfered vertically from parent to child. Researchers also observe that DNA can also be transfered from one organism to a distantly related organism. An extreme case of horizontal gene transfer occurs when two entirely different organisms merge to become one new organism. This type of merger is called endosymbiosis. Because of horizontal gene transfer, we now know that the Tree of Life is really more like a Web of Life.
Open Tree of Life
This project, launched with funding from the National Science Foundation in 2012, will produce an online, comprehensive first-draft tree of data for all 1.8 million named species, accessible to both the public and scientific communities. The biggest challenge to creating this Tree is dealing with horizontal transfer. Maybe this tree is really a network.
Trees of Genes
Many of the images showing the Tree of Life might more properly be called “Trees of Genes” since these trees are based on those genes known to be shared by all organisms. For example, the first trees based on DNA sequence data were based on ribosomes. Later trees used additional genes, but these genes are involved in information handling and don’t reflect the totality of a genome’s evolution.
Evogenao – Leonard Eisenberg’s Tree of Life is a wonderful teaching tool because it contains so many important lessons about biological evolution. Eisenberg created this tree based on information from Richard Dawkins’ book, The Ancestor’s Tale, and from information contained in a various refereed journals.
Circular Tree of Life – This elegant tree, at left, is based on comparisons of 31 conserved genes from 191 species. While the entire genomes of these 191 organisms is known, the researchers only used a small subset of genes to create this tree. These exclusive genes are involved in translation, a group of genes known to have the least amount of lateral gene transfer. To eliminate messiness and ambiguity from their results, they implemented special procedures to exclude instances of horizontal gene transfer. See: Toward automatic reconstruction of a highly resolved tree of life. Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P. Source European Molecular Biology Laboratory, Meyerhofstrasse 1, 69012 Heidelberg, Germany. Science. 2006 Mar 3;311(5765):1283-7.
3-Domains – Carl Woese created a huge breakthrough in understanding the Tree of Life when he compared of DNA sequences from diverse organims. In 1977, Woese published observations that the Tree of Life had three domains. One of these domains is the Archaea, which was previously considered to be closely related to bacteria. To the left is the “Big Tree” created by Norm Pace as an elaboration of Woese’s original work.
Five Kingdoms – While not a tree, this diagram (below) from Roger Whitaker and promoted by Lynn Margulis, was a significant breakthrough in understanding the Tree of Life in the late 1960s because it showed the relationships of fungi, plants, protists and prokaryotes (Monera). Thanks to work in cell biology, scientists were able to make more distinctions based on microscopic features of cells.
Tree of Life Poster – Neal Olander’s Tree of Life poster feature photographs of various creatures, with particular focus on the Eukaryotes. From his site, you may download a 24″x48″ poster in pdf format. Includes a timeline.
Tree of Life Websites
Interactive Tree of Life – This website offers an online tool for the display and manipulation of phylogenetic trees.
Tree of Life Web Pages – The Tree of Life Web Project is one of the most ambitious projects which includes a huge collection of online information about diverse organisms. This Tree is compiled collaboratively by hundreds of expert and amateur contributors.
Encyclopedia of Life – a global effort to document all 1.8 million named species of animals, plants, and other forms of life on Earth. For the first time in the history of the planet, scientists, students, and citizens will have multi-media access to all known living species, even those that have just been discovered.
Discover Life – Tree of Life – This interactive Tree of Life contains contains links to major groups of living things. Discover Life provides free on-line tools to identify species, share ways to teach and study nature’s wonders, report findings, build maps, process images, and contribute to and learn from a growing encyclopedia of life that over a million species pages.
Open Tree of Life – Launched with funding from the National Science Foundation in 2012, this project will produce an online, comprehensive first-draft tree of data for all 1.8 million named species, accessible to both the public and scientific communities.
Books and Articles on Tree of Life
Diversity Of Life: The Illustrated Guide to the Five Kingdoms 1999. ISBN #0763708623.by Lynn Margulis, Karlene Schwartz and Michael Dolan. This coloring book is packed with information about the vast variety of life on Earth.
Woese, Carl, The universal ancestor, Proceedings of the National Academy of Sciences, Vol. 95, Issue 12, 6854-6859, June 9, 1998, http://www.pnas.org/cgi/content/full/95/12/6854
Horizontal and Vertical: The Evolution of Evolution –
Crunching Data for the Tree of Life http://www.nytimes.com/2009/02/10/science/10tree.html