Genetics and Human Variation

Throughout history, humans have been highly mobile creatures. Populations have moved across the landscape, migrated to new regions of the world, and interacted with other groups of people. As they encounter other populations, they may have exchanged genes with other populations through various mating practices causing the shift in their population genetic makeup. This movement of alleles from one population to another is known as gene flow. This exchange of alleles will eventually cause the populations to become more similar genetically over time. As populations increase in size, gene flow causes an increase of variation within populations as new genes are being introduced while causing a decrease in variation between populations.

Many factors can influence gene flow, such as geographic distance, geographic barriers, and nonrandom mating. It has been well documented that geographic space limits gene flow between populations because they have less of a chance of coming into contact with one another. Similarly, geographic barriers have limited gene flow in the past as people migrating on foot generally choose the most efficient way to move across the landscape. This means that landforms, such as mountain ranges and large bodies of water, will interrupt population movement and limit gene flow between groups on either side of the landform.

Nonrandom mating refers to the pattern of mate choice within a population and influence genotype and phenotype frequencies. For example, the creation of social race in the U.S. made it culturally taboo to mate between races for much of our history. This has greatly influence the rate of genetic exchange between social races influencing genetic phenotypic variation within our country.

Due to the vast coverage of people across the world, humans show less genetic diversity than other primates due to our increased ability to exchange genes. Other primates exists in small pockets of the world (i.e. have great geographic space between groups) and, therefore, are limited in their ability to exchange genes and the populations become more genetically diverse over time. The recent development of large genetic databases, such as the Human Genome Diversity Project (HGDP) and 1000 Genomes Project has made it possible for anthropologists to examine the relationships of population genetic structures and phenotype between populations around the world. A link to the HGDP is provided if you would like to learn more about this project.

Overall, population genetic structures are ever-changing and are influenced by many environmental and cultural factors. The rate of gene flow can change over time as culture changes. However, as the human population continues to increase, people are living closer together, and the rate of human movement increases due to improved travel, populations will become more genetically similar due to increased gene flow between groups. Given the relatively low genetic variation in the human population, people who appear to have great phenotypic variation likely are fairly similar genetically.