Tree of Life Project Aims for Every Twig and Leaf
By CARL ZIMMER - THE NEW YORK TIMES
Added: Mon, 04 Jun 2012 20:56:59 UTC
In 1837, Charles Darwin opened a notebook and drew a simple tree with a few branches. Each branch, which he labeled with a letter, represented a species. In that doodle, he captured his newfound realization that species were related, having evolved from a common ancestor. Across the top of the page he wrote, “I think.”
Two decades later Darwin presented a detailed account of the tree of life in “On the Origin of Species.” And much of evolutionary biology since then has been dedicated to illuminating parts of the tree. Using DNA, fossils and other clues, scientists have been able to work out the relationships of many groups of organisms, making rough sketches of the entire tree of life. “Animals and fungi are in one part of the tree, and plants are far away in another part,” said Laura A. Katz, an evolutionary biologist at Smith College.
Now Dr. Katz and a number of other colleagues are doing something new. They are drawing a tree of life that includes every known species. A tree, in other words, with about two million branches.
“I think it is an amazing step forward for our community if it can be pulled off,” said Robert P. Guralnick, an expert on evolutionary trees at the University of Colorado who is not part of the project.
Until recently, a complete tree of life would have been inconceivable. To figure out how species are related to one another, scientists inspect each possible way they could be related. With each additional species, the total number of possible trees explodes. There are more possible trees for just 25 species than there are stars in the universe.
Scientists have overcome this problem by developing computer programs that find the most likely relationship among species without having to consider every possible arrangement. With enough processing power, those computers can now analyze tens of thousands of species at a time.
Yet these studies have thrown spotlights on only small portions of the tree of life. “Nobody has tried to put all these results together,” said the leader of the new effort, Karen Cranston, a biologist at the National Evolutionary Synthesis Center in Durham, N.C.
Last year, Dr. Cranston and other experts gathered at a meeting called by the National Science Foundation, where they came up with a plan for a single tree of life. On May 17, the National Science Foundation announced that it was awarding the team a three-year grant of $5.7 million.
The first goal of the project, known as the Open Tree of Life, is to publish a draft by August 2013. For their raw material, the scientists will grab tens of thousands of evolutionary trees that are archived online. They will then graft the smaller trees into a single big one.
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