DNA ‘switches’ separate Neanderthals from modern humans: study

NEW YORK

How can creatures as different in body and mind as present-day humans and their extinct Neanderthal cousins be 99.84 percent identical genetically?

Four years after scientists discovered that the two species' genomes differ by a fraction of a percent, geneticists said on Thursday they have an explanation: the cellular equivalent of "on"/"off" switches that determine whether DNA is activated or not.

Hundreds of Neanderthals' genes were turned off while the identical genes in today's humans are turned on, the international team announced in a paper published online in Science. They also found that hundreds of other genes were turned on in Neanderthals, but are off in people living today.

Among the hundreds: genes that control the shape of limbs and the function of the brain, traits where modern humans and Neanderthals differ most.

"People are fundamentally interested in what makes us human, in what makes us different from Neanderthals," said Sarah Tishkoff, an expert in human evolution at the University of Pennsylvania, who was not involved in the new study. Discovering the differences in gene activation is "an amazing technical feat," she said, and goes a long way to answering that riddle.

The discovery also underlines the power of those on/off patterns. Together, they add up to what is called the human epigenome, to distinguish it from the human genome. The genome is the sequence of 3 billion molecules that constitute all of a person's DNA while the epigenome is which bits of DNA are turned on or off even as the molecular sequence remains unchanged.

In the last few years, research on the epigenome has shed light on how gene silencing leads to cancer, for instance, and how identical twins with identical DNA sequences can be very different. The epigenome exerts such powerful effects that it is often called the "second genetic code."

Now it has offered clues to what makes modern humans distinct.

Genes for strong limbs

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DNA 'switches' separate Neanderthals from modern humans: study