Gene flow

Gene flow (also known as gene migration) is the transfer of genes from one population to another.

Migration into or out of a population may be responsible for a marked change in gene pool frequencies (the number of individual members with a particular trait). Immigration may result in the addition of new genetic material to the established gene pool of a particular species or population, and conversely emigration results in the removal of genetic material.

Gene flow is not absolute, however, and the idea that desirable and undesirable traits are completely under genetic control—an idea that gave birth to the eugenics movements in the United States in the early 1900s, and in Nazi Germany in the 1930s—is demonstrably incorrect.

It has been demonstrated that the Great Wall of China has hindered the natural flow of plant genes. Examples of the same species which grow on either side have been shown to be genetically different.

There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, and animals tend to be more mobile than plants. Greater mobility of an individual tends to give it greater migratory potential.

Although there is no documentary evidence for gene flow in humans, and it has only been demonstrated in insect populations, genes can flow between species, as when bacterial DNA is transferred to animals or plants.