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Coming into America
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Tracing the Genes 3 pages: | 1 | 2 | 3 |

Written by
Maggie Villiger

July 20, 2004 -- The archaeologists in "Coming Into America" mostly rely on artifacts like tools to help piece together the history of the first Americans. But in recent years, scientists have begun turning to genetic evidence as they trace the earliest human migrations around the globe.

The predominant theory is that modern humans evolved in Africa and then migrated through the Middle East to Europe and Asia, beginning some time between 40,000 and 60,000 years ago. What was the route for early humans into the Americas? Scientists compare the DNA of indigenous people in the New World with that of people in Europe and Asia, looking for similarities. The more alike two people's DNA, the more closely related they are - it's as if tiny maps of our ancient origins are hidden within our cells. Anthropologists are using genetics to figure out where some of the first Americans came from, and when.

Photo of a mitochondrion
Mitochondria -- like the one pictured above -- are found within every cell that produces energy. They retain their own genes from generation to generation.

Mother's side of the family
One group of scientists tracks maternal lineage through what's called mitochondrial DNA (mtDNA). This is genetic material found inside mitochondria - structures within every cell that produce energy. What's useful about mitochondria is that they retain their own genes from generation to generation. Their genes aren't a mixture of those from both parents, like all the other genes in our cells. Instead, mtDNA comes solely from your mother, when some of her mitochondria are included in the egg that eventually becomes you. Everyone, whether male or female, gets their mtDNA from their mom, unchanged.

So mtDNA isn't reshuffled every generation in the normal course of inheritance. What does happen, though, is that over the centuries small mutations take place regularly, that are then passed on to future generations. This is the unique process that scientists take advantage of to help figure out both the age and origins of human populations.

3 pages: | 1 | 2 | 3 |

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