Bacteria can utilize horizontally transferred DNA from other bacterial species to adapt and evolve to their changing environments. Natural transformation is a process that allows bacteria, which are able to express a regulated physiological state of competence, to take up and integrate free DNA from their surroundings. This uptake of DNA does not necessarily depend on DNA sequence, thus, indicating the potential of gene transfer from diverged donor organisms. Barriers active against such interspecies transfer are present at different phases of the transformation process. The functionality of these barriers will be discussed, and seen in relation to mechanisms that may enable bacterial cells to respond to environmental stress by adaptive evolution.