Gilles Didier is a researcher in applied mathematics at the Institut Montpellierain Alexander Grothendieck (IMAG), a joint research unit of the Université de Montpellier and the CNRS, France. He is particularly interested in the modeling of biological evolution. Stéphane Guindon is a researcher at the Computer Science, Robotics and Microelectronics Laboratory of Montpellier (LIRMM), a joint research unit of the Université de Montpellier and the CNRS France. His studies focus on probabilistic models describing evolution at different time scales.