![]() ![]() They built a series of phylogenetic trees using data from individual yeast genes and employed an algorithm derived from information theory to find the areas of greatest agreement among the trees. But given that similar methods have produced trees of life that are rife with contradiction, Rokas and Salichos decided to delve deeper. The resulting tree was accurate according to standard statistical analysis. This involves stringing together all the sequence data from individual species into one mega-gene and then comparing that long sequence among the different species and creating a tree that best explains the differences. They first created a phylogenetic tree using the standard method, called concatenation. They started with 23 species of yeast, focusing on 1,070 genes. Rokas and his graduate student Leonidas Salichos explored that question by evaluating each gene independently and using only the most useful genes - those that carry the greatest amount of information with respect to evolutionary history - to construct their tree. “That poses a question: Why do you have this lack of agreement?” said Rokas. Scientists can rattle off examples of conflicting trees published in the same scientific journal within weeks, or even in the same issue. And we have no idea how some of the earliest animals to branch off the tree, such as jellyfish and sponges, are related to each other. These analyses filled in some of the sparse spots on the tree of life, but considerable disagreement still remains.įor example, it’s not clear whether snails are most closely related to clams and other bivalves or to another mollusk group known as tusk shells, said Rokas. But the last decade has seen an explosion in phylogenetic data, rapidly inflating the data pool for generating these trees. Researchers once used just one gene or a handful to compare organisms. Lining up the DNA of humans, chimpanzees and fish, for example, makes it readily apparent that humans and chimps are more closely related to each other than they are to fish. Building BlocksĪt the most basic level, scientists create phylogenetic trees by grouping species according to their degree of relatedness. “I think it will help us quite a bit in speeding up the reconstruction of the tree of life,” said Khidir Hilu, a biologist at Virginia Tech in Blacksburg. “Historically, the areas of the tree of life that have attracted a lot of attention and disagreement usually have to do with the most interesting episodes,” such as the origins of animals, vertebrates and flowering plants, said Antonis Rokas, a biologist at Vanderbilt University who led the new study.īased on the results of the new algorithm, scientists can select only the most informative genes to build phylogenetic trees, an approach that could make the process more accurate and efficient. They hope the new approach will help to clarify periods of evolution that are potentially the most illuminating but also the most conflicted, such as the Cambrian explosion - the rapid diversification of animal life that occurred about 540 million years ago. To resolve this paradox, the researchers developed an algorithm, based on information theory, to gauge the level of certainty in specific parts of the tree. “We are trying to figure out the phylogenetic relationships of 1.8 million species and can’t even sort out 20 yeast,” he said. “They report that every single one of the 1,070 genes conflicts somewhat,” said Michael Donoghue, an evolutionary biologist at Yale who was not involved in the study. ![]() Indeed, just as the spinal column and limbs created contrasting maps of primate evolution, scientists now know that different genes in the same organism can tell different stories.Īccording to a new study partly focused on yeast, the conflicting picture from individual genes is even broader than scientists suspected. The current version of the tree of life is more like a contentious wiki page than a published book, with certain branches subject to frequent debate. But while the abundance of data has helped resolve some of the conflict surrounding parts of the evolutionary tree, it also presents new challenges. ![]()
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