Who am I?

Our DNA is passed from generation to generation. This genetic information is copied perfectly most of the time, but occasionally small changes (mutations) occur that are then passed on. As groups of humans moved around the world over many thousands of years, they acquired different mutations in their DNA. The more DNA differences there are between different populations, the more distantly related they are.

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Fossils from ancient human populations can be examined using radioisotope dating. This method measures natural radioactivity to determine how long ago the fossils were buried. This information can be used to plot the movement of human populations. Combined with DNA analysis, linguistics and archaeology, fossil evidence is revealing how and when humans populated the planet.

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In 1987, US scientists looked at variations in mitochondrial DNA to trace the origins of the first modern human females. Mitochondrial DNA is passed on by mothers (but not fathers) to their children, and so can be used to trace the female line. Their results supported the 'Out-of-Africa' theory: the mitochondrial DNA of every population in the world today can be traced back to early African mitochondrial DNA. Scientists suggest our most recent common female ancestor lived in Africa about 200,000 years ago.

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All your body's cells contain mitochondria, tiny sausage-shaped 'powerhouses'. Mitochondria have their own small amount of DNA, which make proteins needed to generate energy for the cell. All your mitochondria are copies of the 100,000 that were inside your mother's egg cell, which went on to make you. Your father's sperm also contained mitochondria but they were lost after his sperm entered the egg. So mitochondria are passed from a mother to her sons and daughters, but only her daughters pass them on to their children.

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In 1998, Mike Hammer from the University of Arizona looked at variation in Y-chromosome DNA to trace the origins of the first modern human males. The Y-chromosome is passed by fathers to their sons and is responsible for maleness, so it can be used to track the male line. His results support the 'Out-of-Africa' theory: the Y-chromosome DNA of every man in the world traces back to an early African Y-chromosome. He believes that our most recent common male ancestor lived in Africa around 150-200 thousand years ago.

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