Phylogenetics aims to establish evolutionary relationships between our planet’s organisms and to assemble the Tree of Life. In recent years a ‘high throughput ’ variant of this discipline has seen the light of day: phylogenomics. With the complete genome sequencing of numerous organisms, scientists are now able to compare a large number of genes across various species. Although phylogenomics has already allowed much progress in the reconstruction of the Tree of Life, it can lead to wrong conclusions, as Denis Baurain stresses in an article published in PLoS Biology.

What did the first animal to appear on Earth look like? A simple question to which it is nonetheless difficult to answer. Various scientific disciplines, each with their own approaches, try to go back in time to the very first animal. The best known of these disciplines is palaeontology. Palaeontologists reconstruct the history of Life on Earth on the basis of the relics of the past, fossils. The multitude of living beings who have succeeded one another on Earth have left traces which palaeontologists look for and seek to interpret. Hence, newspapers regularly recount the discovery of a new fossil bearing witness to the past existence of one or other species.

Less well known to the general public, another discipline buckles down to the task of tracing back the evolution of Life: phylogenetics. ‘Phylogenetics is the science which looks to identify evolutionary relationships between living beings with the ultimate goal of reconstructing the Tree of Life from the very origins of Life,’ explains Denis Baurain, a researcher at the Unit of Animal Genomics (GIGA and Faculty of Veterinary Medicine, ULg).  ‘In the case of animals, we would like to discover what our very first ancestor looked like and to know if it was simple or complex,’ continues the researcher, for whom phylogenetics is a genuine passion.

Evolutionary relationships, which are progressively refined with advances in scientific knowledge, are summarised in a phylogenetic tree. On this tree, which roughly looks like a genealogical tree, terminal leaves correspond to extant organisms whilst each internal node stands for the extinct ancestor of deriving branches which represent its descendants. The name of a node is that of the clade formed by this ancestor and all its descendants, and not that of the ancestor in question, which is impossible to identify as it is very unlikely to be a known fossil species in particular.