Résumé
The maximum likelihood approach to molecular was proposed as an alternative to the maximum parsimony method after cases of inconsistency of the latter have been described. The maximum likelihood method relies upon statistical modelling of : sites (columns of a set of aligned sequences) are seen as realisations of a random variable whose distribution depends on evolutionary parameters, including the evolutionary tree. The merits and limits of this approach are discussed. The need for appropriate models is stressed, and an example involving a nonstationary process of DNA sequence evolution is presented, allowing discussion about the thermophilic nature of the common ancestor to extant life forms.