Second Early Human Migration

Modern humans are believed to have originated in Africa and then spread around the globe, migrating first from North Africa into the Middle East about 100,000 years ago. Scientists have now found evidence of a second, later migration out of Africa--from eastern Africa along the coast to southern Asia.

A. Silvanna Santachiara-Benerecetti of the University of Pavia in Italy and colleagues studied DNA contained within mitochondria--tiny structures inside every cell that generate energy for cellular activities--from people living in Africa, Asia and the Middle East.

People living in eastern Africa and Asia have a pattern in their mitochrondrial DNA that is clearly distinct from that found in people living in the Middle East, the scientists report in the December issue of the journal Nature Genetics. This supports the theory that there was a second migration out of Africa about 60,000 years ago along the eastern African coast toward Southeast Asia, Australia and the Pacific islands.

'Seahenge' Dated to 2050 B.C.

In August 1998, a ring of 55 oak timbers surrounding a large upside-down oak tree was discovered in a tidal pool in Holme Next the Sea in Norfolk, England. The structure, dubbed "Seahenge," was believed to have been constructed in the Bronze Age about 4,000 years ago as some kind of ceremonial site. Researchers have now determined the exact age of the monument.

Based on radiocarbon analysis of six samples from the trees and tree rings, Alex Bayliss of the Ancient Monuments Laboratory in London and colleagues determined the central stump dates to 2050 B.C. and was about 150 years old when it was felled, according to a report in the Dec. 2 issue of Nature. That means the site was built at the start of the Bronze Age. The surrounding posts were felled in April to June of the following year, 2049 B.C.

That's consistent with earlier findings that broad marks in the wood were made by metal axes of the type used in the early Bronze Age.

"These people were farmers who cleared much of Britain's forest land, and now we have dated one of their religious temples," David Miles, chief archaeologist for English Heritage, said in a statement. "It is tremendously exciting."

The Mummies' Viral Tale

An international team of scientists has studied the remains of 1,500-year-old Andean mummies to trace the transmission of a virus that causes leukemia and other diseases.

Kazuo Tajima of the Aichi Cancer Center Research Institute in Negoya, Japan, and colleagues from Chile analyzed DNA from the bone marrow of 104 mummies found in northern Chile for traces of the human T-cell leukemia virus type 1 (HTLV-1).

The virus, which like the one that causes AIDS is a retrovirus, is most commonly found in southwestern Japan and in South America.

Ancient DNA from HTLV-1 found in the mummies is similar to that found in people living today in the Andes and in Japan, the researchers found.

"This result provides evidence that HTLV-1 was carried with ancient Mongoloids to the Andes before the Colonial Era," the researchers report in the December issue of the journal Nature Medicine.

"Analysis of ancient HTLV-1 sequences could be a useful tool for studying the history of human retroviral infection as well as human prehistoric migration," they write.

Enzyme Linked to Disease

Scientists in recent years have been studying structures on the ends of chromosomes known as telomeres in the hopes that they will gain insight into cancer and aging. Telomeres appear to shorten every time a cell divides.

Now, scientists have identified the first human disease that appears to be caused by a defect in telomerase, an enzyme that keeps telomeres intact.

Kathleen Collins of the University of California at Berkeley and colleagues studied a rare congenital disease known as dyskeratosis congenita (DKC). By the age of 5, victims start to experience problems with tissues that are constantly replaced, such as skin. Children develop skin lesions, their nails and hair fall out, they develop anemia, and they often die from life-threatening infections or cancer by their twenties or thirties.

These patients have abnormally low levels of telomerase, suggesting that they might benefit from getting supplements of the enzyme, the researchers report in the Dec. 2 issue of Nature.

CAPTION: A structure of carefully arranged oak timbers -- dubbed " Seahenge"--in a Norfolk, England, tidal pool has been dated to 2050 B.C.