The Most Precise Tree of Life Ever Drawn

The first tree of life - the schema designating the evolutionary relationships between all living beings - was created in 1870 by the German scientist Ernst Haeckel. The procedure of mapping the tree more precisely has greatly improved since, especially by taking into consideration the advances in DNA analysis. By comparing and quantifying the resemblances and differences of various genomes, scientists get a direct clue of how evolution has actually taken place. This information is more accurate than any fossil comparison or theoretical scenario about how one animal might have changed into another. However, given the sheer size of the DNA codes, this analysis takes a lot of time and the precise mapping of the entire tree is intricate.

Now a group at the European Molecular Biology Laboratory (EMBL) in Heidelberg has taken the challenge of developing a computational method capable of doing automatically what geneticists have done themselves until now.

Peer Bork, Associate Coordinator for Structural and Computational Biology at EMBL, whose group carried out the project said: "For a long time the overwhelming amount of data (the human genome alone contains enough information to fill 200 telephone books) has made it very difficult to pinpoint the information needed for a high-resolution map of evolution. But our study shows how this challenge can be tackled by combining different computational methods in an automated process."

The study has given some very interesting insights about the common origin of all life. Francesca Ciccarelli and Tobias Doerks of Bork's group identified 31 genes that go back to the earliest forms of organisms. These genes have clear relatives in 191 organisms, ranging from bacteria to humans. By studying the relationships between those genes they managed to depict how life evolved.

"Even using such genes, you might get the wrong answer," says Ciccarelli. "Organisms inherit most genes from their parents, but over the course of evolution, a few have been obtained when organisms swapped genes with their neighbours in a process called horizontal gene transfer (HGT). Obviously, the latter class of genes does not tell you anything about your ancestors. The trick was to identify and exclude them from the analysis."

"This procedure drastically reduced the 'noise' in the data, making it possible to identify as yet unknown details of early evolution," says Tobias Doerks. "For example, 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."

Besides discovering such clues about the earliest forms of life, the study also sets the stage for incorporating into the tree of life various unknown species such as the ones living on the ocean floor or in the soil. "With the new high-resolution tree in hand, it is now possible to classify genetic material from this unexplored microbial world and further our understanding of life on the planet", said Bork.

Photo credit: George Carruth