For the first time, scientists have demonstrated that a coevolutionary process is dependent on ecological conditions. Researchers in France studied two bacteria — a predator and a prey — over 300 generations in a controlled environment. Under certain conditions, the prey becomes resistant to the predator, which itself evolves so that it can attack this new prey. In addition, the scientists issued a warning against the previously envisaged use of this predator (Bdellovibrio bacteriovorus) as a “living antibiotic” because, like other antibiotics, this could lead to the selection of resistant pathogenic bacteria.