For the past 26 years, Dr. Luigi Cavalli-Sforza has been the leading researcher on the genetics of the world's human population . In 1994, he and Paolo Menozzi and Alberto Piazza published a book entitled The History and Geography of Human Genes (Princeton University Press), which gave the first synthesis of his research in this fascinating area.
Cavalli-Sforza began by stating that his research is preliminary because at the time it was begun, the technology had not yet been developed enough to allow him to conduct resea as it is done today. Therefore, he hopes his work will induce people to conduct more research in this area of genetics. His work is a basis on which people can study genetic variation, l archeology and linguistics with genetics.
To understand Cavalli-Sforza's discussion, one must first understand the concept of genetic distance and genetic drift. Genetic distance is the percentage difference of the occurrence of a certain gene type between different regions. These distances can then be plotted on a map to show the concentrations, and thereby movements, of that type of gene (i.e. genetic drift). Such mapping of genetic distance can help explain historical events and natural selection. For example, the Duffy gene is found in a 100 percent concentration in mid-Africa, and the frequency declines as one moves away from this area. It is thought that the reason for such a high concentration of this gene in this one area is because the Duffy Gene gives resistance to a special type of malaria, which is carried by a specific parasite common in this area. This is a simplified example of natural selection.
Another example is the RH negative gene, which is found in only a small number of today's population. Cavalli-Sforza displayed a map of the world, on which was depicted his work on the frequency of the RH negative gene. The people of the Basque region have a greater than 50 percent concentration of the RH negative gene,. The frequency decreases in relation to the dstance from the Basque region into the rest of the world until there is very little evidence of this gene. This genetic mapping helps to show that a mutation from RH positive to RH negative occurred somewhere in the Basque area of Europe maybe as much as 40,000 years ago, as he discussed later. The mutation could have happened in one individual and then spread throughout the entire population. The mutation and consequent spread could have occurred because this gene enhanced some characteristic or trait that was helpful to the individual. This is the process of natural selection.
Cavalli-Sforza then went on to discuss genetic distance mapping and how it relates to archeological finds by discussing the population theory popular among paleontologists today. According to Cavalli-Sforza , there were two real origins of humans in Africa. Some 2.5 million years ago, homo erectus appeared with five times less brain capacity than modern man. However, he was walking on two legs so his hands were free for making stone tools. By 100,000 a new species appeared that looked similar to modern humans. This group spread from Africa to the east by boat along coastal routes. Some 50-60,000 years ago these people arrived in New Guinea. In Asia it took longer for this new species to settle because of the colder climate and the need to travel overland to reach this area. Approximately 12,000 years ago this species populated Asia and traversed the Bering Sea over the then-present land bridge to the Americas, migrating to the tip of South America.. Europe was occupied by these new, more modern humans approximately 40,000 years ago. Before this invasion into Europe, the continent was home to the Neandertals.
Cavalli-Sforza showed that one can calculate the time that it took for these early peoples from Africa to travel to the diverse regions of the world by using genetic distancing. He showed slides of charts to prove his point.
The Principal Component was the first method used to synthesize genetic distancing. Cavalli-Sforza began his early research in this area working only with the frequency of blood types found in specific regions. One can plot the data from the blood types onto charts. Cavalli-Sforza introduced this blood-type data in chart form using two principal components (two axes), and found that when the blood samples are compared between groups of people representing the major continents, the six African populations points fall relatively close together, as do the Asian populations. European populations are mixed and not as distinguishable as are the South East Asians, Oceanians, and Native Americans. When a third component is added (third axis), the population samples fall into identifiable groups. This separation becomes heightened as different components, or axes, are added.
Cavalli-Sforza posited that the origin of agriculture was a response to hunger. Approximately 10,000 years ago people began to realize that they could no longer gather sufficient food only by hunting and gathering. There could also have been a change in the flora, fauna, weather patterns, or a dramatic population increase which effected the available food resources. Thus, people began domesticating plants and animals by initially cultivating local plants and herding sheep. The centers of this activity were in the Middle East, Northeastern China adjacent to Korea, and southern Mexico.
According to Cavalli-Sforza, the first agriculture in the Near East was practiced in present-day Turkey. Agriculture arrived in England only 4,000 years later and spread slowly. Contrary to today's understanding that agricultural concepts migrated, he posited that agriculture was brought by people who^M migrated to less settled areas, thus displacing the settled people. The increased agricultural production allowed for improved nutrition and subsequent population growth, which therefore spawned migration.
Genetic distancing maps show almost identical patterns between genetic distancing and the spread of agriculture in Europe. It is fortunate that wheat and barley could be cultivated easily in Europe. This was not true south of the Sahara, and this is why one does not see a similar pattern of agricultural or population expansion into this area.
Thus, to combine the concept of components with the isolation of the Basques which began the discussion, Cavalli-Sforza introduced actual, historical influences which effected the genetic make-up of Europe:
* The first component to influence European genetics was the migration from the Near East in conjunction with the spread of agriculture.
* The second component was the migration of people who spoke a Uralic language from east of the Urals.
* The third component was the migration of peoples from the steppes east of the Urals who arrived in Europe approximately 5-6,000 years ago . These people had domesticated and were riding the horse, and also possessed the weaponry of the early Bronze Age populations. Because of their new mode of transportation they conquered large expanses of territory, traveling into Europe and into India from the Steppe, thus spreading the Indo-European language and customs into these regions.
* The fourth component consisted of at the migration of peoples from Greece who colonized southern Italy.
* The fifth component consisted of a population contraction. As the number of farming communities increased in Europe, many regional groups became confined to specific regions. Thus, the Basque's ancestors became isolated and increasingly concentrated in the Pyrennes Mountains. That is why the Basques have a different language which might not have changed for 30,000 years.
Cavalli-Sforza then moved on to discuss a map of Asia. Through genetic distance mapping, one could see four basic expansions into the Indian sub-continent.
* The first was from the Middle East as people migrated due to the expansion of agriculture, as about 9,000 years ago, agriculture became highly developed in the Indian region.
* Then agriculture was abandoned, partly due to the fact that the Indus Valley underwent a climactic change. At this time the Aryan peoples, who were pastoral nomads, moved in from Europe. These people became today's upper caste in Indian society. These expansions by European peoples into India happened approximately 5,000 years ago. At this same time one also saw a spread of nomadic pasturalism from the steppe regions occurred, thereby creating another caste of people in today's India.
* Later, the Mongols, Turks and Timurids came across the steppes. These three groups were of extreme Mongolian types (wide face, heavy eyelids, small eyes, small nostrils and nose, shorter limbs - perfectly adapted to living in extreme cold climates.) They were also skilled in the steppe art of warfare.
* From Japan and Korea came a westward migration. This region of Asia had developed pottery some 12,000 years ago; however, agriculture came late (only 2,000 years ago). Prior to agriculture, these people were basically hunters and fishermen. A demographic explosion due to agricultural growth could have provided the impetus for their migration into the Indian region.
All of these components lead to a highly mixed region in Central Asia.
Cavalli-Sforza then provided a linguistic picture of middle Asia. The Altaic group of languages consists of four subgroups: Turkic, Mongol, Manchu and Tungus. This group is somehow related to the Uralic language family of Finnish, Estonian and Hungarian. These languages arrived rather late into Central Asia. There are also Tokarian speakers who se presence as Indo-European speakers on the doorstep of China has not yet been satisfactorily explained This was probably the language spoken by the people who Dr. Kamberi is studying in the Xinjiang region. (Please refer to lecture synopsis for "Caucasian Mummies.") Later in 1632 AD, the Arab civilization began to grow and formed an overlay in Central Asia. By 715 AD, the Arabs (Muslims) had defeated the Chinese in today's Kyrgyzstan and the Tarim Basin. In 1250 AD the Mongol Empire came to fore.
The progress of the Russians has again brought European genes into the area. By 1800 all of Central Asia had become the territorial interests of Russia. However, the Russian and then the Soviet policy of displacing populations has led to a genetic mess in terms of mapping genetic distancing. Cavalli-Sforza is in the process of collecting DNA samples from Central Asia, and should have more exact conclusions later.
The last slide presented by Cavalli-Sforza was of the silkroad as it was 2,000 years ago. According to him, the early Europoid, Tokarian-speakers who migrated into this area perhaps 4,000 years ago. Today's Uighurs have a high percentage of Mongol genes because those early Europoids mixed with the Turkic people who came later. However, Cavalli-Sforza said that some Central Asian ethnic groups today, such as the Kazaks, have less Europoid mixture than others, primarily because they remained on the steppes and had less interaction with the Europoid Iranian city dwellers.
In conclusion, Cavalli-Sforza believes that the scientific community must start from scratch in collecting data worldwide and must utilize the new techniques and technologies now available to gain more precise data and conclusions. Thus far, not much work has been done in Central Asia proper, but he feels it would provide a wealth of genetic information.