Think about it. As you travel back in time though your family history, the number of ancestors you have roughly doubles with every generation. Using the most conservative estimate of generation time — 32 years — in the year 1152, you had as many as 134,217,728 potential ancestors. And since genes are scrambled with every generation, it’s very likely you share little to no genetic relation to most of them. They might as well be strangers!
DNA companies use two DNA tests, a Y-chromosome DNA which provides information about your male line ancestry, and a mitochondrial DNA (mtDNA) test which provides information about your female line ancestry. These tests supposedly yield more accurate information, but they still suffer from major pitfalls. For example, if two males have similar DNA on their Y-chromosome, they likely share a more recent common ancestor than individuals with dissimilar DNA, but any estimate of when or that common ancestor lived and who they are is almost entirely speculative. Mitochondrial DNA tests are similarly limited. The rate of mutation in the whole mtDNA genome is one to three percent per generation, so the time gap between mutations could be as many as 100 generations. This means that a lot of people share the same mtDNA, and their common ancestor could be as close as one generation or as far as fifty or more.
DNA testing companies often take this ambiguity and fill in the blanks with impressive stories that you can show your friends and relatives. Though fascinating, these tales share more in common with astrological horoscopes than historical accounts.
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