Unknown human relative found

LOS ANGELES – DNA from a 40,000-year-old pinkie finger, belonging to a child and found in a cave in Siberia, indicates that the bone is from a previously unknown family of human relatives that lived among Neanderthals and modern humans, German researchers reported Wednesday.

The discovery, if confirmed by research already under way, would mark the first time that an entirely new species of hominid has been identified solely on the basis of DNA sequencing, the team reported online in the journal Nature. It also suggests that other currently unknown species could be similarly identified.

With the recent, and still controversial, discovery of the hobbit-like species Homo floriensis that survived in Indonesia until about 13,000 years ago, the evidence now indicates that at least four species of human-like creatures walked the Earth at the same time. The find suggests that “40,000 years ago, the planet was more crowded than we thought,” wrote evolutionary biologist Terence A. Brown of the University of Manchester in an editorial accompanying the report.

The new species shared a common ancestor with both modern humans and Neanderthals about 1 million years ago, based on the DNA sequences, according to the team led by anthropologists Johannes Krause and Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. That is about 500,000 years older than the last common ancestor shared by Neanderthals and modern humans.

“I like it because it makes us sort of a normal mammal,” said anthropologist Todd R. Disotell of New York University’s Center for the Study of Human Origins, who was not involved in the research. “At every other phase of evolutionary history, there has always been multiple species at any one time,” both for humans and other species. “We just happen to be the last one standing.”

The DNA sequences are from mitochondria, the tiny organelles within cells that provide power for all the activities of life. They thus provide a useful indicator of lineage but say little about the physical characteristics of the whole organism. And because the researchers have only the finger bone, found in the Altai Mountains in 2008, they are unable to draw any broader conclusions about its identity.

But Krause and his colleagues are now working feverishly to sequence the much-more-difficult-to-analyze DNA in the nucleus of cells in the hopes that that information will provide a much better picture of the new form of life they appear to have discovered.

Until the team has a complete sequence of nuclear DNA, “we are not saying this is a new species,” Paabo said at a news conference. But all the evidence so far suggests it is, he added.

The pinkie bone, from a child age 7 to 9 but of unknown gender, was found in the Denisova Cave in southern Siberia. The location is critical primarily for climatic reasons. While most hominid fossils have been found in equatorial regions, the heat and humidity of such places rapidly degrades DNA, making any sequencing problematic, if not impossible.

But DNA is preserved much better at higher altitudes and in colder climates.

The Denisova Cave shows signs of being occupied by humans and their relatives periodically for at least 125,000 years. The pinkie was found in a layer of soil and debris dating from 48,000 to 30,000 years ago. Bracelets and other ornamentation were also found in the layer, but experts cautioned that there is no evidence linking them to this specific bone.