Welcome to the age of ancient DNA sequencing

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A cave in Iran where the bones of ancient human farmers were found. Their DNA was sequenced to unlock the mystery of who the earliest farmers were in the region. (credit: FEREIDOUN BIGLARI)

The greatest technological revolution in human history arguably happened about 12,000 years ago, when humans first stopped living as hunter gatherers and became farmers. This so-called Neolithic Revolution transformed human culture, our genomes, and our ecosystems. But the origins of farming have remained a mystery. Was there one eureka moment, when an early Neolithic person realized the seeds they scattered in fall had sprouted into grains two seasons later? Or, more intriguingly, did several groups of people start farming independently?

Two new studies published this month in Science and Nature magazines use DNA analysis of ancient human bones to conclude that farming arose in multiple regions simultaneously. The Science study focused on four farmers who lived between 9,000 and 10,000 years ago in the mountainous Zagros region of Iran. The Nature study analyzed 44 individuals (farmers as well as hunter-gatherers) from Armenia, Turkey, Israel, Jordan, and Iran who lived between 14,000 and 3,500 years ago. By sequencing parts of these ancient people’s DNA, researchers could determine their likely ancestry as well as what populations are descended from them today. The researchers conclude that there are at least two groups of ancient humans who discovered farming separately in the Middle East and then exported the Neolithic revolution across large parts of the continent.

The secrets of ancient DNA

Over the past decade, modern DNA sequencing techniques have allowed scientists to recover strands of genetic material from decayed bones that have been infused with microbes over thousands of years. Now, those techniques are widely accessible and highly refined. It starts with how researchers pick their bones. If possible, they’ll extract DNA from the petrous bone in the inner ear, a goldmine for genetic material that can yield roughly 100 times more ancient DNA than other parts of the skeleton. Then researchers use a process called in-solution hybridization, which uses special probes made from DNA or RNA that attach to the desired ancient human DNA, fishing it out of a soup of other genetic material from other organisms that accumulated in the decomposing bone. Techniques like these are making it easier than ever for us to sequence ancient DNA and reconstruct the human past.

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