Microevolution is defined as the changes that occur within a population over time. Usually when the evolution of a population is observable, it is considered microevolution because it’s taking place during a shorter number of generations. This does not create a new species, but rather a different variation. By contrast, Macroevolution is when two species come together to create a new one. There are four different processes that can occur over the course of a small number of generations. These processes are mutation, natural selection, gene flow and genetic drift. Mutations in species affect the DNA sequences of a cell’s genome while natural selection involves the heritable traits a species has that make it easier for them to survive and reproduce. The process of Genetic drift is an evolutionary process, which causes changes in allele frequencies over time; it might actually cause gene variants to disappear completely, which in turn reduces genetic variability. The forth aspect of microevolution is Gene flow which is the exchange of genes between populations, these are commonly of the same species.
One classic example of microevolution taking place is with the North American Sparrow. Not originally native to America, they were introduced in 1852. Over time, they have evolved in variations of color and size as they spread to the northern and southernmost parts of the U.S. Larger bodies allow the species to survive in lower temperatures. The birds that migrated to the south are smaller in size because of the warmer weather. The selection of larger bodied sparrows in colder climates is an example of natural selection.
Another Example of natural selection is the evolving resistance found in bacterial strands. Pests to Pesticides, Weeds to Herbicides, Pathogens to Medicine are all good examples occurring currently that scientist have been observing. A Bacterium strain contains large populations and short generation times cause a very quick resistance to the medicines we use to fight them off. Because of the large populations within the strands there are more and more combinations generated within the strands increasing the odds of a resistance to the antibiotics used to fend them off. Natural selection selects the strands holding the resistance within them. Bacteria is constantly adapting to our defenses causing the scientist who try to prevent them to constantly play catch up.
Other examples of this process would be the mosquito, which is evolving to resist common pesticides such as DDT, this is also the case with whiteflies. Essentially, microevolution affects us all. From the medicine we take in, to the food we eat, and even the lawns surrounding your home are constantly evolving to the world around it. One thing is always constant, and that is change.