"The recovery of history is really a jigsaw puzzle," said Peter Underhill, PhD, senior research scientist in the department of genetics and one of the study's authors. "You have to look at genetics, material culture (archeological findings), linguistics and other areas to find different lines of evidence that reinforce each other."
The researchers' mathematical analysis showed that a pair of mutations on the Y chromosome, called Eu9, predicted the presence of certain figurines from the Neolithic period with 88 percent accuracy and the presence of painted pottery with 80 percent accuracy. The study is published in the September issue of Antiquity.
"The strength of the association is very surprising," said Roy King, MD, PhD, associate professor of psychiatry and behavioral sciences at Stanford who co-authored the study. "The genetic measures are very precise, and archaeology is pretty precise - either a figurine is there or it isn't. The strength of the correlation is driven by the strength of our measures."
It is known that agriculture spread from the Middle East to Europe during the Neolithic period about 12,000 years ago, but for many years archeologists have debated how this occurred. Was it due to the movement of people or to the movement of ideas? Previous genetic analysis of people living today suggests a migration - that the people moved - but critics have questioned this view. The latest study reinforces evidence of a migration in which people brought their ideas and lifestyle with them.
Genetics can answer the question in a roundabout way. Human DNA sequences today may shed light on our ancestors because some portions of the human genome change very slowly. One of these is the Y chromosome. Women carry two X chromosomes, while men have one X and one Y. The X and Y cannot exchange DNA like the 22 pairs of non-sex chromosomes in humans or the paired X chromosomes in women. As a result, a man should have a carbon copy of the Y chromosome of his father, grandfather and so on. But sometimes a harmless mutation, a misspelling in the genetic code, occurs. The mutation will be passed on to all the man's male descendants. If millions of men have the same mutation, then they all share a distant paternal ancestor.
Underhill studies pairs of mutations on the Y chromosome in current populations. He combines data about the geographic distribution of the mutations with information about when the mutations arose to trace historical migrations.
While reading a previous paper on Y-chromosome mutations in Science that Underhill co-authored, King thought the geographic distribution of some pairs of mutations paralleled that of Neolithic decorative ceramics. King, a psychiatrist with a PhD in mathematics and a deep interest in art history, called Underhill and suggested they compare the two sets of data.
Critics argue that the contemporary gene pool does not reflect what happened thousands of years ago because people have moved around too much since then. Many also see genetics as an entirely separate line of investigation from archaeological work. Researchers had compared genetic studies to language evolution, but no one had attempted to link genetics and material culture. Underhill agreed to undertake the analysis with King.
The Science paper Underhill co-authored described the Y chromosomes of more than 1,000 men in 25 different Middle Eastern and European geographic regions. They found that the frequency of four pairs of mutations was highest in the Middle East but also significant in eastern and southern Europe. While it is likely that all the mutations studied originated prior to the Neolithic period, the distribution suggested a westward migration.
The researchers took the distribution of the four pairs of Y-chromosome mutations found to originate in the Middle East and compared it to the regions where certain decorated ceramics have been found in Neolithic sites. They focused on figurines and pottery with painted geometric and abstract designs. Most of the figurines are female; researchers have speculated that they were used for magic or religious purposes, as amulets or charms, or even as dolls for children, King said.
The researchers found a strong correlation in their study between the Y-chromosome mutations and the presence of certain artifacts. Nonetheless, Underhill remains cautious. "No gene on the Y chromosome is going to program you to make pottery," he said. Instead, the Y-chromosome mutation pairs used in the study are simply population markers that in this case were compared to ceramics. The same mutations could be compared to many different types of artifacts.
King and Underhill hope that archaeologists will follow them in trying to blend these two lines of historical evidence. They are continuing to gather genetic data from areas in Greece near Neolithic archaeological sites and in western Turkey, which researchers believe to be the jumping-off point for Neolithic migration.
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