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We're all mutants, say scientists
Each of us has at least 100 new mutations in our DNA, according to research published in the journal Current Biology.
Scientists have been trying to get an accurate estimate of the mutation rate for over 70 years.
However, only now has it been possible to get a reliable estimate, thanks to "next generation" technology for genetic sequencing.
The findings may lead to new treatments and insights into our evolution.
In 1935, one of the founders of modern genetics, JBS Haldane, studied a group of men with the blood disease haemophilia. He speculated that there would be about 150 new mutations in each of us.
Others have since looked at DNA in chimpanzees to try to produce general estimates for humans.
However, next generation sequencing technology has enabled the scientists to produce a far more direct and reliable estimate.
They looked at thousands of genes in the Y chromosomes of two Chinese men. They knew the men were distantly related, having shared a common ancestor who was born in 1805.
By looking at the number of differences between the two men, and the size of the human genome, they were able to come up with an estimate of between 100 and 200 new mutations per person.
Impressively, it seems that Haldane was right all along.
Unimaginable
One of the scientists, Dr Yali Xue from the Wellcome Trust Sanger Institute in Cambridgeshire, said: "The amount of data we generated would have been unimaginable just a few years ago.
"And finding this tiny number of mutations was more difficult than finding an ant's egg in an emperor's rice store."
New mutations can occasionally lead to severe diseases like cancer. It is hoped that the findings may lead to new ways to reduce mutations and provide insights into human evolution.
Joseph Nadeau, from the Case Western Reserve University in the US, who was not involved in this study said: "New mutations are the source of inherited variation, some of which can lead to disease and dysfunction, and some of which determine the nature and pace of evolutionary change.
"These are exciting times," he added.
"We are finally obtaining good reliable estimates of genetic features that are urgently needed to understand who we are genetically."
Galaxy's 'cannibalism' revealed
The vast Andromeda galaxy appears to have expanded by digesting stars from other galaxies, research has shown. When an international team of scientists mapped Andromeda, they discovered stars that they said were "remnants of dwarf galaxies". The astronomers report their findings in the journal Nature.
This consumption of stars has been suggested previously, but the team's ultra-deep survey has provided detailed images to show that it took place. This shows the "hierarchical model" of galaxy formation in action. The model predicts that large galaxies should be surrounded by relics of smaller galaxies they have consumed.
The scientists charted the outskirts of Andromeda in detail for the first time. They discovered stars that could not have formed within the galaxy itself. Pauline Barmby, an astronomer from the University of Western Ontario, Canada, who was involved in the study, told BBC News the pattern of the stars' orbits revealed their origin. "Andromeda is so close that we can map out all the stars," she said. "And when you see a sort of lump of stars that far out, and with the same orbit, you know they can't have been there forever."
Andromeda, which is approximately 2.5 million light-years from Earth, is still expanding, say the scientists. The researchers also saw a "stream of stars" of a nearby galaxy called Triangulum "stretching" towards Andromeda. Dr Scott Chapman, reader in astrophysics at the Institute of Astronomy, University of Cambridge, UK, was also involved in the research. He said: "Ultimately, these two galaxies may end up merging completely.
- "Ironically, galaxy formation and galaxy destruction seem to go hand in hand."
Nickolay Gnedin, an astrophysicist from the University of Chicago, US, who was not involved in this study, described the work as showing "galactic archaeology in action".