The Tree of Life was an expression used by Charles Darwin to describe the diversity of organisms on Earth and their evolutionary history. There are only two life forms, eukaryotes, which gather their genetic material in a nucleus, and prokaryotes, such as bacteria, which have their genetic material floating freely in the cell. Until recently, eukaryotes, which include humans, were divided in five groups. But now, European researchers have found that the Tree of Life has lost a branch. After doing the largest ever genetic comparison of life forms, they concluded that there are only four groups of eukaryotes. But read more...
You can see on the left how the Tree of Life has lost a branch. (Credit: University of Oslo, Norway) As said one of the researchers about their study, "all non-bacterial life on Earth -- called eukaryotic life -- can now be divided into four main groups instead of the five groups that we have been working with up to now."
The University of Oslo team was composed of three researchers of the Centre for Ecological and Evolutionary Synthesis (CEES), Professor Kjetill Jakobsen, Associate Professor Kamran Shalchian-Tabrizi, and PhD Student Marianne Aastebøl Minge. They've worked with other scientists of the Department of Zoology and Animal Biology and of the Department of Genetic Medicine and Development, at the University of Geneva, Switzerland.
So how exactly did they conduct their research? Let's read Apollon, the University of Oslo research magazine. "The findings come from the largest ever genetic comparison of higher life forms on the planet. Of 5,000 genes examined, researchers identified 123 common genes from all known groups of organisms; these common genes have been studied more closely. The study has required long hours of work from the researchers and an enormous amount of computing resources -- supplied through a large network of computers at the University of Oslo."
Here is how life forms are now classified. "All life on Earth can be divided into two essentially different life forms -- eukaryotes and prokaryotes. The eukaryotes gather their genetic material in a nucleus, while the prokaryotes (bacteria and archaea) have their genetic material floating freely in the cell. Eukaryotic organisms -- such as humans -- can, as a result of the new findings, be divided into the following four categories:
- Plants (green and red algae, and plants)
- Opisthokonts (amoebas, fungi, and all animals—including humans)
- Excavates (free-living organisms and parasites)
- SAR (the new main group, an abbreviation of Stramenophiles, Alveolates, and Rhizaria, the names of some of its members)"
And here are more 'philosophical' explanations about the Tree of Life. [It] "tells the story of life on Earth, and our research can say something about how quickly life developed. Our discovery suggests that there were fewer big 'events' than we have previously assumed in the development of higher life forms. The more we know about the branches on the Tree of Life, the more we can find out about life's Big Bang, the beginning of life on Earth," says Shalchian-Tabrizi. "Three billion years ago, there was only bacteria and Archaea. Eukaryotic life, which comprises all multi-celled organisms, developed in the sea -- probably between 1.2 and 1.6 billion years ago. It was not before about 500 million years ago that the first creatures crept onto land."
For more information, this research work has been published by PLoS ONE, an open-access scientific journal, on August 29, 2007 under the title "Phylogenomics Reshuffles the Eukaryotic Supergroups." You also can read this Wikipedia page. Finally, I recommend a visit to the Tree of Life Web Project. "The Tree of Life Web Project (ToL) is a collaborative effort of biologists from around the world. On more than 9000 World Wide Web pages, the project provides information about the diversity of organisms on Earth, their evolutionary history (phylogeny), and characteristics." But be warned: you might be overwhelmed by the variety of topics and spend lots of time on this site -- at least if you're interested in this subject.
Sources: Lars Hoff, Apollon, University of Oslo research magazine, January 21, 2008; and various websites
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