Cousins

Some geneticists are claiming that we are all descended from a single small band of people who left Africa perhaps 65,000 years ago. Nicholas Wade has the story in the NY Times:

Everyone in the world can be placed on a single family tree, in terms of their mitochondrial DNA, because everyone has inherited that piece of DNA from a single female, the mitochondrial Eve, who lived some 200,000 years ago. There were, of course, many other women in that ancient population, but over the generations one mitochondrial DNA replaced all the others through the process known as genetic drift. With the help of mutations that have built up on the one surviving copy, geneticists can arrange people in lineages and estimate the time of origin of each lineage....

Although there is general, but not complete, agreement that modern humans emigrated from Africa in recent times, there is still a difference between geneticists and archaeologists as to the timing of this event. Archaeologists tend to view the genetic data as providing invaluable information about the interrelationship between groups of people, but they place less confidence in the dates derived from genetic family trees....

Dr. Macaulay's team has been able to estimate the size of the population in Africa from which the founders are descended. The calculation indicates a maximum of 550 women, but the true size may have been considerably less. This points to a single group of hunter-gatherers, perhaps a couple of hundred strong, as the ancestors of all humans outside of Africa, Dr. Macaulay said.

As the story is presented here, it seems a bit too deterministic: I doubt that a group of 200 ppl would have decided one day that the neighborhood had gone to hell so they'd all head for Australia. Still, the basics are interesting.