Sunday, January 19, 2014

Ancient DNA sparks new mystery

it.” DNA from a 400,000-year-old leg bone is breaking records. It also raises questions about how closely ancient humanlike creatures were related to each other. The genetic material is four times older than any other recovered from a pre-human ancestor, or hominid. And scientists say the DNA links this individual, recovered from Spain, with a much later humanlike group called Denisovans. Their remains have been found only in East Asia’s Siberia.

The newly studied leg bone turned up nearly a decade ago. Scientists retrieved it from among
the fossil remains of at least 28 individuals. All were found in a cave in Spain known as the “pit of bones.” All belonged to a humanlike species that resembled people but existed long before them.

A species is a group of living things that can produce offspring that can survive and reproduce. All species — from people to boa constrictors to red maples — evolve. That means they change slowly over long periods of time. This change, or adaptation, usually occurs in response to natural variations in DNA. A long and spiral-shaped molecule, DNA is found inside almost every cell of the body. It holds the operating instructions that tell a cell what to do. Each parent passes along half of his or her DNA to any offspring. So when DNA morphs, as it often does, offspring can inherit these altered cellular instructions.

Matthias Meyer studies the DNA instructions, or genes, of ancient species at the Max Planck Institute in Leipzig, Germany. His team’s new discoveries from the ancient leg bone were published Dec. 4 in Nature.

Most scientists consider bones from the Spanish pit to be the remains of a species known as Homo heidelbergensis. This hominid may be an ancestor of Neandertals, an ancient species that roamed Europe. What stunned the scientists was the leg bone’s genetic links to Denisovans.

A finger bone and two teeth found in Siberia — far from Spain — are the only known evidence of Denisovans. And those fossils indicate Denisovans lived more than 350,000 years after the leg bone’s owner.

Two types of DNA carry the genetic material in each individual. The form found inside a cell’s nucleus contains genes inherited from both parents. A second type of DNA possesses material passed along only from a child’s mother. It’s found outside the nucleus, in mitochondria (MI toh KON dree ah). These are segments of a cell where energy is produced. Meyer’s team focused on this mitochondrial DNA.

John Hawks at the University of Wisconsin-Madison studies ancient humanlike species. The new DNA study makes a surprising connection between ancient humanlike groups, he told Science News. However, he said, it also raises important questions about where and how those hominids might have come together.

Concludes Hawks: “The Denisovan connection is fascinating, but I’m cautious about how to interpret it.

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