Adaptive mutation was re-proposed in 1988 by John Cairns who was studying "Escherichia coli" that lacked the ability to metabolize lactose. He grew these bacteria in media in which lactose was the only source of energy. In doing so, he found that the rate at which the bacteria evolved the ability to metabolize lactose was many orders of magnitude higher than would be expected if the mutations were truly random. This inspired him to propose that the mutations that had occurred had been "directed" at those genes involved in lactose utilization.</ref>