 To give an example: perhaps the most famous result from Lenski’s long-term evolution experiment is the origin of citrate utilization in just one of the twelve E. coli lineages (Blount et al. 2008). Citrate is present in the bacterial growth medium and is a potential energy source, but one that E. coli lack the ability to use aerobically (i.e., in the presence of oxygen)—or, at least they were unable to, until around 31,500 generations into the experiment when one strain accumulated the mutations relevant to growing on citrate. This new capacity gave the population a relative advantage over non-citrate-eating strains.