Explosions of biodiversity under the microscope

‘We are empiricist methodologists in a kind of way. We identify the fuzziest and most complicated areas of the Tree of Life and tackle them one after the other in order to assemble a complete tree,’ points out Denis Baurain. Besides homoplasy and orthology issues, specialists in phylogenetics are confronted with other difficulties. ‘At the dawn of the Cambrian, 550 million years ago, there was probably an explosion of animal diversity. Yet it is sometimes difficult to retrace the chronology of events which occur so rapidly,’ continues the researcher. Episodes of brutal diversification indeed pose problems for specialists. During these episodes, organisms evolve rapidly to remain competitive and colonise new ecological niches. This is what is called adaptive radiation. ‘That was the case notably for modern mammals, which have diversified in very little time,’ adds Denis Baurain. Moreover, like yeast, living beings can evolve in a regressive direction, which means they lose in complexity in comparison with their ancestors. ‘That is why parasites are often wrongly thought to be primitive organisms.’

Homoplasy, gene duplication and transfer, adaptive radiation, regression; evolutionary history is far from being a walk in the park, which it is easy to trace back. But, phylogenomics – ‘provided that it is used appropriately,’ stresses Denis Baurain – is very effective and should enable specialists to one by one solve the mysteries of the Tree of Life.