Tree of life

New technique sheds fresh light on the origin of species

By Kirtiman Awasthi
Published: Friday 31 March 2006

a group of scientists at the European Molecular Biology Laboratory (embl) in Heidelberg, Germany, has developed a computational method to reconstruct the tree of life -- a representation of evolution and the relationships between different life forms.

The tree of life was developed by German biologist Ernst Haeckle in 1870. It is based on the theory of evolution proposed by Charles Darwin. Human beings figure at the top of the tree, reptiles in the middle and bacteria at the base. However, uncertainty remains over the position of bacteria and other microbes.

The tree of life has several uses including tracking the origin and spread of emerging diseases and their vectors, bio-prospecting for pharmaceutical and agrochemical products and evaluating risk factors for species conservation and ecosystem restoration.

The new model is based on genetic information available for different species. dna sequences of complete genomes provide us with a direct record of evolution," says Peer Bork, who headed the project. The researchers identified 36 genes universally present in 191 species whose genomes have been sequenced to reconstruct their relationship. This tree can also be easily automated and updated. The study was published in Science (Vol 311, No 5765, March 3, 2006).

Using this open source resource, the authors looked at the evolutionary history of bacteria. They found that Acidobacteria (group of ecologically important bacteria) was a sister group of Proteobacteria (a group of mostly pathogenic bacteria). The study confirmed the hypothesis on the origin of bacteria. We now know that the first bacterium was probably a type called gram-positive and likely lived at high temperatures -- suggesting that all life arose in hot environments, the researchers say. Another finding was that smaller genomes evolve faster than bigger ones.

According to the theory of evolution, all organisms descended from a common ancestor and so share common genes. But some of the genes may have been laterally transferred. Organisms inherit most genes from their parents, but over the course of evolution, organisms swap genes with each other through horizontal gene transfer (hgt)," says Francesca Ciccarelli, the lead author. Because hgt does not tell anything about ancestors, the researchers identified and excluded them from the analysis.

The researchers now expect to classify microbes from unexplored regions like the ocean floor to further improve understanding of life on the planet. This may also help resolve the evolution versus creationism debate.

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