Experimental evolution is the use of experiments or controlled field manipulations to explore evolutionary dynamics. Evolution may be observed in the laboratory as populations adapt to new environmental conditions and/or change by such stochastic processes as random genetic drift. With modern molecular tools, it is possible to pinpoint the mutations that selection acts upon, what brought about the adaptations, and to find out how exactly these mutations work. Because of the large number of generations required for adaptation to occur, evolution experiments are typically carried out with microorganisms such as bacteria, yeast or viruses, or other organisms with rapid generation times. However, laboratory studies with foxes and with rodents (see below) have shown that notable adaptations can occur within as few as 10-20 generations and experiments with wild guppies have observed adaptations within comparable numbers of generations. More recently, using experimental evolution followed by whole genome pooled sequencing, an approach known as Evolve and Resequence (E&R) is becoming popular in fruit flies.