Geneticists Trace Migration of Mideast Agriculturists to Europe

By Kurt Holden

"[Dr. Cavalli-Sforza] finds that after the introduction of agriculture in the Middle East about 10,000 years ago, farmers from there spread at the rate of one kilometer, or five-eighths of a mile, a year, eventually settling throughout Europe. "

—Louise Levathes, New York Times July 27, 1993

The world generally credits the Sumerians, who lived in the marshlands created by the Tigris and Euphrates rivers in southern Iraq, with the development of civilization. Although nearly contemporary river valley civilizations also developed in the Nile Valley of Egypt and the Indus Valley of Pakistan, the Sumerians seem to have been the first people to live in cities and to create a system of writing.

Scientists also regard the "fertile crescent," an arc linking Iran, Iraq, Syria, Lebanon, Jordan and Israel/Palestine, as the site of the earlier "neolithic revolution," when hunter-gatherers first learned to plant crops, and then created permanent settlements to cultivate, guard and harvest them. The evidence is the fact that wild ancestors of the food crops associated with traditional Middle Eastern and European agriculture are native to the fertile crescent.

Pinpointing the Birth of Agriculture

Now archeologists maintain they have pinpointed the time agriculture was born to just over l0,000 years ago, and the place to within a 100-mile radius of the Dead Sea, between present-day Jordan and Israel. Meanwhile, from unrelated studies, some biological scientists conclude that the agricultural technology developed in that period subsequently spread from the Middle East to northernmost and westernmost Europe not through cultural diffusion, but through actual migrations of the Middle Eastern people who developed it.

According to these scientists, who have examined the genetic makeup of modern populations throughout Europe, agricultural people spread from Turkey as far afield as Finland, Sweden and Ireland, intermarrying with the less numerous hunter-gathering clans they found occupying those lands in a migration that continued for some 6,000 years.

Dr. Frank Hole, an archeologist, and Joy McCoriston, an archeobotanist, both of Yale University, described in American Anthropology in March of 1991 the circumstances under which they believe agriculture was born. Starting around 12,000 BC, they wrote, the summertime climate in the Levant became increasingly hot and dry, reducing the supply of wild game and vegetation and drying up the small lakes upon which foraging people, who already were familiar with wild grain, had depended for water.

Core samples from the ancient lakes indicate the change in climate caused a shift toward Mediterranean-type vegetation, with leathery, water-retaining leaves. Annual grasses, which complete their life cycle in the spring with large seeds in hard cases that will endure through a dry season to germinate with the return of moisture, increasingly replaced perennial vegetation.

The time of this change represented a "convergence" of historical accidents, according to Dr. Hole. "People are ready, they have technology adapted to plant foods," he explained. "The plants themselves are proliferating. And the climate requires people to overcome long periods when foods are not available."

No such earlier convergence has been found elsewhere, according to the Yale scientists, who focused their study upon people of the Natufian culture, named after an archeological site in present-day Palestine called Wadi Al-Natuf. At the time of the climate change, the Natufians had developed the flint sickles and stone mortars and pestles needed to harvest and process wild grains and, based upon the seashell badges of rank found in their tombs, had a developed social structure.

They built stone houses and, the two scientists suspect, it was they who exploited a genetic mutation that occurred within the area's wild einkorn wheat as they began to plant and harvest it. In the wild, most of the wheat stalks shed their grains separately, which made them difficult to collect. Just over 10,000 years ago, however, a mutation had occurred that caused grains in a tiny percentage of the wheat to become fatter and stick more tenaciously to the stalk. The Natufians apparently saved for replanting a portion of the seeds they harvested, and, because the intact heads were less likely to be lost in the fields and more likely to be collected by the Natufians, each year an increasing percentage of the wheat planted was of the new and more nutritious variety.

No such domesticated seeds have yet been found in Natufian sites. Carbonized remains of domesticated grains have been recovered, however, from settlements inhabited by the immediate successors, and biological descendants, of the Natufians. Based upon mathematical calculations, scientists believe the change from wild einkorn wheat to the domestic variety could have been accomplished quite naturally by an agricultural people in as few as 22 years. Hole and McCoristan say the evidence points to the Natufians as the people who carried out this revolution.

Not only did the Natufians begin to live in well-constructed stone houses, but scattered hunting camps they formerly maintained for brief occupancy disappear from the archeological record. The record also shows, right after the end of the Natufian culture, the rapid spread not only of domesticated wheat, but also of barley, peas and beans. Scientists estimate that this first agricultural revolution spread northward into Turkey and Mesopotamia at the rate of about one kilometer per year. Animals were domesticated about 1,000 years later.

This theory of the exact time and place of the domestication of plants is, however, still disputed, as is another relatively new theory that the agriculturists carried the new techniques of agriculture with them as they multiplied and spread out from the scene of its invention. This hypothesis questions the earlier and still widely held theory of cultural diffusion, whereby neighboring hunter-gatherer clans would observe what the agriculturists were doing, and then adopt the techniques themselves.

Early Farmers and the Spread of Languages

The cultural diffusion theory was sharply challenged by the publication in May 1991 in the British journal Nature of an analysis of the genetic make-up of people at some 3,300 sites across Europe. The analysis was undertaken by Dr. Robert R. Sokal, Dr. Neal L. Oden and Chester Wilson of the State University of New York at Stony Brook. It established that, progressing from southern Turkey, near where agriculture originated, toward northern Europe, certain genes become scarcer in the human populations.

These results support the theory that as an original population pressed outward, intermarrying with hunter-gatherer populations in its path, its original genes were only gradually diluted. The present-day biological gradient also correlates with what is known of the spread of agriculture, whose routes and timing have been established from the archeological record.

This record indicates agriculture being practiced in eastern and central Turkey around 10,500 years ago, in western Turkey between 7,500 and 8,000 years ago, in southern Europe between 7,000 and 7,500 years ago, Central Europe 6,000 to 6,500 years ago, France and north Germany 5,500 to 6,000 years ago, Sweden and Russia 5,000 to 5,500 years ago, and in the British Isles and Finland between 4,500 and 5,000 years ago.

The hypothesis that genetic and cultural change moved in tandem from the Middle East through the Balkans as agriculture enabled populations to increase and forced them to seek new land was first proposed several years ago by Dr. Luca L. CavalliSforza and Dr. Robert J. Ammerman at Stanford University. They argued that agriculture was transmitted by the physical movement of people, not by the exchange of information.

Dr. Colin Renfrew, an archeologist at Cambridge University in England, seized upon this hypothesis for his own theory that Indo-European languages were not spread throughout Europe, Iran and northern India by successive waves of warlike conquerors from the area of the present-day Ukraine, but evolved from the language carried with the agriculturists.

This association of Indo-European languages with advancing agricultural people from the Middle East is hotly disputed, however. Archeologist Marija Gimbutas of the University of California at Los Angeles, an exponent of the belief that the Indo-Europeans were conquerers, disputes the idea that their language may have been spread by agricultural migration.

"It is more complicated than that," Dr. Gimbutas maintains. In some areas of Spain and France as well as in parts of Eastern Europe, she says, farming was successfully transmitted without migration of the farmers themselves. She therefore finds Dr. Renfrew's hypothesis on the spread of Indo-European languages "not acceptable. "

In fact, it is the theories of Cavalli Sforza and Gimbutas that are easily reconciled. The former believes that the sole direct survivors of the agriculturists who started spreading from the Middle East 10,000 years ago are the Basques of southwestern France and adjacent areas of Spain. Their language is unrelated to any other spoken in Europe.

This clears the field for Dr. Gimbutas' hypothesis that between 6,000 and 4,000 years ago, horsemen migrated very rapidly out of the steppes of southwestern Russia, spreading their Kurgan culture and the original Indo-European language across a Europe already occupied by the remnants of hunter-gatherers and by the Middle Eastern agriculturists who had largely replaced them.

Dr. Cavalli-Sforza's genetic survey supports this incursion. "We discovered an area of population expansion that almost perfectly matched Gimbutas' projection for the center of Kurgan culture," he explains.

Commenting imaginatively in Nature on the agricultural migration model of Ammerman and Cavalli-Sforza, Dr. J.S. Jones of University College, London, writes that the impact of the migrations of ever-increasing agricultural people on the hunter-gatherers who were in their path must have resembled "a process of gentrification—or even yuppification—from the east." The evidence gathered by evolutionary biologist Sokal and his colleagues, however, indicates that the hunter-gatherers who survived the meeting of cultures were absorbed into the advancing population of farmers. These studies, Jones writes, demonstrate that in their biological make-up modern Europeans "still reflect the migrations of ancient farmers who spread from the Middle East."

Kurt Holden, a retired film-maker, divides his time between Washington, DC and the Mideast.