On this background, the concept of horizontal gene transfer between organisms emerged at the beginning of the 1990s as an alternative explanation for those conflictive phylogenetic events ( Hilario & Gogarten 1993). 1953), and the theoretical potential of cross-species gene transfer in evolution was soon proposed ( Syvanen 1985). On the other hand, mechanisms for the transfer of genetic material between micro-organisms were well known from the beginning of molecular biology and molecular genetics research ( Lederberg & Tatum 1946 Zinder & Lederberg 1952 Stocker et al. 1998), by grouping together species or species groups that are split by other morphological, physiological or molecular markers. It was soon realized, however, that different genes could lead to phylogenetic incongruence and conflictive phylogenies, mainly in micro-organisms ( Hilario & Gogarten 1993 Gupta & Singh 1994 Golding & Gupta 1995 Whitehouse et al. One of these molecular markers, the sequence of 16S RNA genes, was proposed to be a good tool for reconstructing old phylogenetic relationships ( Woese et al. In this review, I will discuss how horizontal gene transfer fits in with current evolutionary thinking, as well as the challenges that it proposes for the current evolutionary paradigm.Īt the beginning, the founders of molecular phylogenetics used molecular information from different proteins and genes to reconstruct phylogenetic relationships between organisms ( Zuckerkandl & Pauling 1965). But these acquisitions are primarily non-genealogical, questioning, in my opinion, the neo-Darwinian conception of a gradualist process driving the appearance of novel traits and functions. ![]() In this sense, it is a mechanism that permits the acquisition of evolutionary novelties. Horizontal gene transfer, ‘the non-genealogical transmission of genetic material from one organism to another’ ( Goldenfeld & Woese 2007), is a source of new genes and functions to the recipient of the transferred genetic material. 2008), is an important force driving the evolution of Bacteria and Archaea, as well as that of unicellular eukaryotes, and should therefore also be considered as part of the structure of any evolutionary synthesis. Today it seems evident, from the studies discussed below, that horizontal (or lateral) gene transfer, the direct visualization of which has been achieved recently ( Babić et al. Recently, several calls have been put forward for a new evolutionary synthesis ( Dean & Thornton 2007 Pigliucci 2007 Carroll 2008 Koonin 2009) that encompasses mechanisms other than mutation, natural selection and drift to explain evolutionary changes, such as developmental constraints and epigenetic modifications among others. Finally, I discuss how horizontal gene transfer fits in the current neo-Darwinian evolutionary paradigm and conclude there is a need for a new evolutionary paradigm that includes horizontal gene transfer as well as other mechanisms in the explanation of evolution. Moreover, I discuss the feasibility of reconstructing ancient phylogenetic relationships in the face of horizontal gene transfer. ![]() I review recent literature, asking, first, which processes are involved in the evolutionary success of transferred genes and, secondly, about the extent of horizontal gene transfer towards different evolutionary times. In this paper, I review the current standpoint on horizontal gene transfer in evolutionary thinking and discuss how important horizontal gene transfer is in evolution in the broad sense, and particularly in prokaryotic evolution. The contribution of horizontal gene transfer to evolution has been controversial since it was suggested to be a force driving evolution in the microbial world.
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