What is genetic anthropology?

Genetic anthropology is an emerging discipline that combines DNA and physical evidence to reveal the history of ancient human migration. It seeks to answer the questions, "Where did we come from, and how did we get here?"

DNA studies indicate that all modern humans share a common female ancestor who lived in Africa about 140,000 years ago, and all men share a common male ancestor who lived in Africa about 60,000 years ago. These were not the only humans who lived in these eras, and the human genome still contains many genetic traits of their contemporaries. Humanity's most recent common ancestors are identifiable because their lineages have survived by chance in the special pieces of DNA that are passed down the gender lines nearly unaltered from one generation to the next. These ancestors are part of a growing body of fossil and DNA evidence indicating that modern humans arose in sub-Saharan Africa and began migrating, starting about 65,000 years ago, to populate first southern Asia, China, Java, and later Europe. Each of us living today has DNA that contains the story of our ancient ancestors' journeys.

The Story of Human Migration Also is Told in the DNA of Parasites and Pets.

Recent studies of bacteria called Streptococcus mutans, which cause tooth decay, reveal that distinct lineages of the bacteria exist in different geographic regions of the world. The geographical distribution of these lineages reflects the pattern of human migration from the ancestral homeland in Africa. S. mutans is transmitted almost entirely from human mother to child during birth, resulting in the preservation of its lineages over thousands of years. S. mutans is only one of many types of human parasites whose DNA lineages follow the pattern of human migration.

The correlation with human migration is present but less distinct for pets. Studies of domestic cats’ mtDNA reveal that they share a most-recent common ancestor who lived in the Middle East about 70,000 to 100,000 years ago. Wild cats, motivated by the desire to get mice and other food from humanity’s first farmers, seem to have domesticated themselves about 10,000 to 12,000 years ago. Genetic markers in house cats’ mtDNA reveal that the cats followed the same migratory patterns as early human farmers.

How do genes tell the story of our ancient ancestors' migrations?

When DNA is passed from one generation to the next, most of it is mixed by the processes that make each person unique from his or her parents. Some special pieces of DNA, however, remain virtually unaltered as they pass from parent to child. One of these pieces is carried by the Y chromosome, which is passed only from father to son. Another piece, mitochondrial DNA (mtDNA), is passed (with few exceptions) only from mother to child. Since the DNA in the Y chromosome does not mix with other DNA, it is like a genetic surname that allows men to trace their paternal lineages. Similarly, mtDNA allows both men and women to trace their maternal lineages.

Both the Y chromosome DNA and mtDNA are subject to occasional harmless mutations that become inheritable genetic markers. After several generations, a particular genetic marker is carried by almost all male and female inhabitants of the region in which it arose. When people leave that region, they carry the marker with them. By studying the genes of many different indigenous populations, scientists can trace when and where a particular marker arose. Each marker contained in a person’s DNA represents a location and migration pattern of that person’s ancient ancestors.

For example, roughly 70% of English men, 95% of Spanish men, and 95% of Irish men have a distinctive Y-chromosome mutation known as M173. The distribution of people with this mutation, in conjunction with other DNA analyses, indicates that the men's ancestors moved north out of Spain into England and Ireland at the end of the last ice age.

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