Evolutionary change and phylogenetic relationships in light of horizontal gene transfer

Horizontal gene transfer has, over the past 25 years, become a part of evolutionary thinking. In the present paper I discuss horizontal gene transfer (HGT) in relation to contingency, natural selection, evolutionary change speed and the Tree-of-Life endeavour, with the aim of contributing to the understanding of the role of HGT in evolutionary processes. In addition, the challenges that HGT imposes on the current view of evolution are emphasized.The author has been supported by a grant of Spanish DGI (CGL2013-41375-P).Peer reviewe