When people travel to another area and successfully mate with people in the
population there, a transfer of genes occurs between the populations even though the
traveler returns home. For example, when U. S. soldiers had children in Southeast Asia
with Vietnamese women during the war there in the 1960's and early 1970's, they
altered the gene pool frequencies of the Vietnamese population.
This is an example of..
bottle neck
natural selection
coevolution
gene flow