All humans are mutants, a new study suggests

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Researchers in Britain and China are using a new method to measure the rate of genetic mutation among humans — and it seems that all people in the world likely carry at least some new mutations.

For their study, published this week in the journal Current Biology, the researchers enlisted the help of two Chinese men whose families have lived in the same village for centuries. The two men are relatives, separated by 13 generations, and have a common ancestor believed to have been born around 1805. Because the human Y chromosome is passed down from father to son unchanged, except in the case of rare mutation, the researchers were able to analyze differences in the distant relatives’ versions of the Y chromosome, and then estimate the rate of human mutation from them.

That technique requires new and sophisticated sequencing technology. With the technology, the researchers discovered 12 mutations between the two men’s Y chromosomes. Eight were shown to have occurred in the lab, which means that four had occurred naturally in the family some time during the last 200 years, and were then passed down from generation to generation.

Based on their findings, the researchers estimate that human mutation probably occurs at a rate of about one mutation per 33 million nucleotides per generation. (This corroborates earlier, cruder estimates of the mutation rate.) Given the colossal number of nucleotides contained in a single person’s DNA, however, this rate suggests that every human should probably have some of their own unique genetic mutations. Don’t worry. They’re almost all totally harmless. But greater knowledge of human mutation is crucial for understanding the history of human evolution — and for understanding how humans differ from one another.