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Is carbon dating accuracy

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The work was funded by the Howard Hughes Medical Institute. A family tree of Indo-European languages suggests they began to spread and split about 9,000 years ago.

Scientists attempt to date genetic changes by tracing back to such spread, using a statistical model that assumes genes have a certain mutation rate over time."No matter how we [changed] the analysis or assumptions, we couldn't get a date of around 6,000 years," says Gray."This kind of study is exactly what linguistics needs," says April Mc Mahon, who studies the history of languages at the University of Sheffield, UK. So suggests new research that tracked changes in two genes thought to help regulate brain growth, changes that appeared well after the rise of modern humans 200,000 years ago.That the defining feature of humans — our large brains — continued to evolve as recently as 5,800 years ago, and may be doing so today, promises to surprise the average person, if not biologists."A different way to look at is it's almost impossible for evolution not to happen." Still, the findings also are controversial, because it's far from clear what effect the genetic changes had or if they arose when Lahn's "molecular clock" suggests — at roughly the same time period as some cultural achievements, including written language and the development of cities.

Lahn and colleagues examined two genes, named microcephalin and ASPM, that are connected to brain size.

"The genetic evolution of humans in the very recent past might in some ways be linked to the cultural evolution," he said.

Other scientists urge great caution in interpreting the research.

If those genes don't work, babies are born with severely small brains, called microcephaly.

Using DNA samples from ethnically diverse populations, they identified a collection of variations in each gene that occurred with unusually high frequency.

That does not mean one population is smarter than another, Lahn and other scientists stressed, noting that numerous other genes are key to brain development.