Wednesday, January 30, 2008

Blue-eyed humans have a single, common ancestor

New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.

What is the genetic mutation
“Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes”. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. The switch’s effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour – a condition known as albinism.

Limited genetic variation
Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.” Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.

Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour.

Nature shuffles our genes
The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”

Friday, January 18, 2008

Polynesians: Genetic Relationship to Melanesians

The origins and current genetic relationships of Pacific Islanders have generated interest and controversy for many decades. Now, a new comprehensive genetic study of almost 1,000 individuals has revealed that Polynesians and Micronesians have almost no genetic relation to Melanesians, and that groups that live in the islands of Melanesia are remarkably diverse.

The study, “The Genetic Structure of Pacific Islanders,” is published in the January issue of PLoS Genetics (http://www.plosgenetics.org). It involved researchers from Temple, University of Maryland, Yale, Binghamton University, the Marshfield Clinic Research Foundation, Victoria University in New Zealand, Mackay Memorial Hospital in Taiwan, and the Institute for Medical Research in Papua New Guinea.

The researchers analyzed more than 800 genetic markers (highly informative microsatellites) in nearly 1,000 individuals from 41 Pacific populations, as opposed to prior small-scale mitochondrial DNA or Y chromosome studies, which had produced conflicting results.

“The first settlers of Australia, New Guinea, and the large islands just to the east arrived between 50,000 and 30,000 years ago, when Neanderthals still roamed Europe,” says Jonathan Friedlaender, professor emeritus of anthropology at Temple and the study’s lead author. “These small groups were isolated and became extremely diverse during the following tens of thousands of years. Then, a little more than 3,000 years ago, the ancestors of the Polynesians and Micronesians, with their excellent sailing outrigger canoes, appeared in the islands of Melanesia, and during the following centuries settled the islands in the vast unknown regions of the central and eastern Pacific.

“Over the last 20 years there have been many hypotheses concerning where the ancestors of the Polynesians came from in Asia, how long it took them to develop their special seafaring abilities in Island Melanesia, and how much they interacted with the native Melanesian peoples there before they commenced their remarkable Diaspora across the unexplored islands in the Pacific,” he adds.

According to Friedlaender, one scenario called the ‘fast train hypothesis,’ which is supported by the mitochondrial evidence, suggests that ancestors of the Polynesians originated in Taiwan, moved through Indonesia to Island Melanesia, and then out into the unknown islands of the Pacific without having any significant contact with the Island Melanesians along the way. A counter argument called ‘slow boat hypothesis,’ which the Y chromosome evidence supports, suggests that the ancestors of the Polynesians were primarily Melanesians, and that there was very little Asian or Taiwanese influence. A third position, called the “entangled bank hypothesis,” suggests these ancient migrations simply can’t be accurately reconstructed by looking at the genetics of today’s populations, even in the context of the available archaeological evidence.

In their paper, the researchers state that their analysis is consistent with the scenario that the ancestors of Polynesians moved through Island Melanesia relatively rapidly and only intermixed to a very modest degree with the indigenous populations there.

“Our genetic analysis establishes that the Polynesians’ and Micronesians’ closest relationships are to Taiwan Aborigines and East Asians,” says Friedlaender. “Some groups in Island Melanesia who speak languages related to Polynesian, called Austronesian or Oceanic languages, do show a small Polynesian genetic contribution, but it is very minor – never more than 20 percent.

“There clearly was a lot of cultural and language influence that occurred, but the amount of genetic exchange between the groups along the way was remarkably low,” he says. “From the genetic perspective, if the ancestral train from the Taiwan vicinity to Polynesia wasn’t an express, very few passengers climbed aboard or got off along the way."

Friedlaender adds that this study also confirms and expands their findings from previous studies about the genetic diversity of Island Melanesians—among the most genetically diverse people on the planet, showing further that their diversity is neatly organized by island, island size, topography and language families.

Thursday, January 17, 2008

First Temple Seal Found in Jerusalem

A stone seal bearing the name of one of the families who acted as servants in the First Temple and then returned to Jerusalem after being exiled to Babylonia has been uncovered in an archeological excavation in Jerusalem's City of David, a prominent Israeli archeologist said Wednesday.

A crescent moon, the symbol of the chief Babylonian god Sin, appears on the top of the altar.

Under this scene are three Hebrew letters spelling Temech, Mazar said.

The 2,500-year-old black stone seal, which has the name "Temech" engraved on it, was found earlier this week amid stratified debris in the excavation under way just outside the Old City walls near the Dung Gate, said archeologist Dr. Eilat Mazar, who is leading the dig.

According to the Book of Nehemiah, the Temech family were servants of the First Temple and were sent into exile to Babylon following its destruction by the Babylonians in 586 BCE.

The family was among those who later returned to Jerusalem, the Bible recounts.

The seal, which was bought in Babylon and dates to 538-445 BCE, portrays a common and popular cultic scene, Mazar said.

The 2.1 x 1.8-cm. elliptical seal is engraved with two bearded priests standing on either side of an incense altar with their hands raised forward in a position of worship.

The Bible refers to the Temech family: "These are the children of the province, that went up out of the captivity, of those that had been carried away, whom Nebuchadnezzar the king of Babylon had carried away, and came again to Jerusalem and to Judah, every one unto his city." [Nehemiah 7:6]... "The Nethinim [7:46]"... The children of Temech." [7:55].

The fact that this cultic scene relates to the Babylonian chief god seemed not to have disturbed the Jews who used it on their own seal, she added.

The seal of one of the members of the Temech family was discovered just dozens of meters away from the Opel area, where the servants of the Temple, or "Nethinim," lived in the time of Nehemiah, Mazar said.

"The seal of the Temech family gives us a direct connection between archeology and the biblical sources and serves as actual evidence of a family mentioned in the Bible," she said. "One cannot help being astonished by the credibility of the biblical source as seen by the archaeological find."

The find will be announced by Mazar at the 8th annual Herzliya Conference on Sunday.

The archeologist, who rose to international prominence for her recent excavation that may have uncovered King David's palace, most recently uncovered the remnants of a wall from Nehemiah.