The Japan Times
November 1, 2000

Japanese form unique genetic group due to long isolation, study says

Modern genes point to African origins

PARIS (AFP-Jiji) The groundbreaking theory that Homo sapiens originated in Africa before slowly spreading across the world has been powerfully backed by new research into variations in the male sex chromosome.

The "out of Africa" hypothesis, sketched in 1987, is based on mitochondrial DNA — scraps of genetic tissue only inherited from the maternal side — that were found in ancient fossils.

This suggested that modern man first appeared on the scene in Eastern Africa about 150,000 years ago, leaving between 35,000 and 89,000 years ago on a relentless push in which the species eventually conquered the planet.

A major research effort from scientists in eight nations, published Monday in November's issue of the U.S. journal Nature Genetics, has now validated the theory, and in so doing has devised a potent tool to probe the very earliest origins of mankind.

The team drew up a genetic family tree of mankind thanks to small variations in the genes of 1,062 men in communities around the world.

The researchers identified 167 markers — specific genetic sequences called alleles located in the Y chromosome, one of the two sex chromosomes (X and Y) which only men carry. Women carry two X chromosomes.

Variations in these markers corresponded astonishingly to the geographical location of where the men live.

In other words, the markers reflected the waves of human migration that unfolded across the world over tens of thousands of years. Each ripple caused a tiny disturbance in the male gene pool as the species intermingled and the Y chromosome adapted to the process of natural selection.

Samples were taken from men in 22 geographical areas in countries that included Pakistan, India, Cambodia, Laos, Australia, New Guinea, the U.S., Mali, Sudan, Ethiopia and Japan.

Their allele mutations were then assembled into 10 types, called haplogroups.

Like branches off a family tree, they show a migration from Eastern Africa into the Middle East, then Southern and Southeast Asia, then New Guinea and Australia, followed by Europe and Central Asia. Among the findings:

The findings "take historical population genetics, or 'archaeogenetics,' a quantum leap forward," says a commentary in Nature Genetics by a team from the McDonald Institute for Archaeological Research in Cambridge.

The research was especially important, given that it came from DNA of living populations rather than genetic material teased out of rare fossils, it said.

The technique was to take samples of genetic tissue, amplify them and then search for the markers using a chromatographic analysis.

The study was led by Peter Underhill of California's Stanford University.