Microevolution is a process that results in a change in gene frequency within a population over a relatively short amount of time. It is due to gene flow, selection, and genetic drift. Common examples include the peppered moth and bacterial resistance to antibiotics. For example, in pre-industrial revolution England, there were mainly white peppered moths, with the frequency of black moths approaching 1 percent. Once soot covered the trees in those areas of England, due to factory smoke, the white moths stood out against the darker trees and due to natural selection, birds consumed mostly white moths leaving behind the black ones, that blended into the background. The gene frequency increased for the darker variety and for the white moths, it decreased. Eventually, due to microevolution, the population became mostly black. However, when clean air laws were established, the frequency shifted yet again, to white moths. This is microevolution. A new species doesn't result, however, particular adaptive traits will increasely occur in the population. Macroevolution on the other hand, takes place over a geologically longer period of time, where small accumulated changes result in the formation of a new species. An example of macroevolution is the Horse. It went from a small dog-sized herbivore and eventually, through mutation and adaptive radiation, went through the transitional stages of toes to hooves and short limbs to the long limbs horses possess today. Pressures from a changing environment and selection for particular mutations resulted in modern day horses.