3.Genetic Archaeology

Relevance of genetic archaeology


Colin Renfrew was the first historian to identify the relevance of genetics to archaeology and coined the term Archaeo-genetics. Now this field of Archaeo-genetics is giving lot of information about ancient people, which could not be determined earlier. As discussed in the first chapter of this book, the gene-mapping is helping the biology scientists to trace out the origin and movements of ancient people. Now, the time has come that historians also accept it as an important source of information and modify their theories about Stone Age, copper age and Iron Age history. Still depending only on the evidences of Stone Age artefacts for reconstruction of historical events is boring and without any kind of vitality and enthusiasm. Just like the acceptance of radio carbon dating as a tool in historical research, gene-mapping also should be adapted as a new tool in this field of archaeology. 

Luigi Luca Cavalli-Sforza 

Luigi Luca Cavalli-Sforza (born January 25, 1922) is an Italian born in Genoa, and completed his graduation from Ghislieri College in Pavia (Italy) in 1939 and he received his M.D. from the University of Pavia in 1944. His post-war studies at Cambridge in the area of bacterial genetics were followed by years of teaching in northern Italy, in Milan, Parma, and Pavia. He moved into Stanford University, USA in the year 1970 and found the intellectual culture more open-ended and cooperative, and where he has remained. In 1999 he won the Balzan Prize for the Science of human origins. 
Cavalli-Sforza has summed up his work for laymen in the book titled “Genes, Peoples, and Languages”. Cavalli-Sforza was one of the first scientists to ask whether the genes of modern populations might contain an inherited historical record of the human species. The study of demographics was already well-established, based on linguistic, cultural, and archaeological clues, but it had become overlaid with nationalist and racist ideologies. Cavalli-Sforza initiated a new field of research by combining the concrete findings of demography with a newly-available analysis of blood groups in an actual human population. Cavalli-Sforza has studied the connections between migration patterns and blood groups.


Cavalli-Sforza and Edwards worked together in determining various branches of human genetic divergences. The study on genetic differences among various sections of people and in various countries gave a tree like patterns of genetic divergence of human populations. Historical separation of populations and spread of genes among populations by migration and admixture distinctly created a genetic pattern and Cavalli-Sforza was the first scientist to hypothesize on human migration pattern based on genetic studies. (Wikipedia)

 

Human Genome Project

            
The Human Genome Project (HGP) was an international scientific research project with a primary goal to determine the sequence of chemical base pairs which make up DNA and to identify and map the approximately 20,000-25,000 genes of the human genome from both a physical and functional standpoint. This project was started in the year 1990 and was completed in the year 2000 by the university of California Genome Bioinformatics Group. A working draft of the genome was released in 2000 and a complete one in 2003, with further analysis still being published. Most of the government-sponsored programmes on gene-sequencing were performed in universities and research centres from the United States, Canada, New Zealand and Britain. The mapping of human genes is an important step in the development of medicines and other aspects of health care. It is an important mile stone on the point of genetic archaeology also; but government authorities play down the relevance of HGP to this field of genetic archaeology. Because, there is a notion that genetic profiling of a person may be used as a weapon against a person if his racial roots are known. Further it may create racial problems in multi ethnic societies. 


While the objective of the Human Genome Project is to understand the genetic makeup of the human species, the project also has focused on several other non-human organisms such as E. coli, the fruit fly, and the laboratory mouse. It remains one of the largest single investigational projects in modern science. The "genome" of any given individual is unique; mapping "the human genome" involves sequencing multiple variations of each gene. The project did not study the entire DNA found in human cells; some heterochromatic areas (about 8% of the total) remain un-sequenced. (wikipedia)

Key findings of Genome Project   

                  There are approximately 30,000 genes in human beings, the same range as in mice and twice that of roundworms. Understanding how these genes express themselves will provide clues to how diseases are caused. All human races are 99.99 % alike, so racial differences are genetically insignificant. This could mean all humans are descended from a single original mother.  Most genetic mutations occur in the male of the species and as such are agents of change. They are also more likely to be responsible for genetic disorders.  Genomics has led to advances in genetic archaeology and has improved our understanding of how we evolved as humans and diverged from apes 25 million years ago.        (wikipedia)    

Patterns of genetic variation carry human history

                  Because of the controversy over the Human Genome Diversity Project, the federal government of USA has so far granted the project relatively little funding. The large-scale effort envisioned by Cavalli-Sforza has not occurred.  Small-scale investigations of genetic variation are thriving in Europe and other countries. The Centre for the Study of Human Polymorphism, based in Paris, now offers DNA samples from populations around the world for research. And the growth of the Internet is changing how genetics research is done.  But genetics research is also producing results of an entirely different kind. Differences in DNA sequences from person to person reflect the cumulative effects of human history. The patterns of genetic variation in the world today therefore carry a record of that history. They document the evolution of an African ape that began walking on two legs about four million years ago. They record the existence, sometime between 100,000 and 200,000 years ago, of a small group of people who are the ancestors of every person alive today. They chronicle the origins of "races" and "ethnic groups" and describe how those groups have both blended and separated over time. (Olson, 2001)

Genetic Engineering

                  A series of experiments done at the Stanford University and elsewhere transformed anthropological genetics during the 1990s. The Stanford biochemist Stanley Cohen and biochemist Herbert Boyer of the University California at San Francisco figured out how to cut DNA in precise locations, combine DNA from different organisms, and grow the resulting hybrid DNA in bacteria. For the first time, human beings could control DNA nucleotide by nucleotide. The process of DNA cutting and poymerisation is being called as genetic engineering and the age of bio-technology had begun. (Olson, 2001)

Evolution of Modern Humans

                      Fewer than 10,000 generations separate everyone alive today from the small group of Africans who were our common ancestors. That's much more than the twenty or so generations mentioned in Genesis, but it's the blink of an eye in evolutionary terms. Even over thousands of generations human groups have not differentiated in any substantial way. Rather, the genetic evidence indicates that modern human beings have expanded as a single, relatively well mixed population without subsequent genetic bottlenecks (bottlenecks tend to erase the evidence of previous bottlenecks, which is how geneticists know that the bottleneck in Africa was the most recent one). Our comparative youth as a species accounts for our extreme genetic homogeneity. The chimpanzees living on a single hillside in Africa have twice as much variety in their DNA as do the six billion people scattered across the globe.

                     Finally, as we learn more about our genetic susceptibilities to disease and our relationship to the past, we need to find better ways of putting genetics in context. People tend to attribute great importance to the findings of geneticists. But the striking homogeneity of our DNA actually emphasizes the centrality of the environment and our experiences in determining who we are. Because culture exerts such a profound influence on complex traits, our genetic heritage has little importance in considerations of ethics or public policy. For almost a decade Cavalli-Sforza has been trapped in the paradox at the heart of human genetics. The only way to understand how similar we are is to learn how we differ. Yet any study of human differences seems to play into the hands of those who would accentuate those differences. Researchers might claim that the genetic differences they identify among groups have no biological significance. Yet simply by dividing human beings into categories like sub-Saharan Africans, Jews, Germans, or Australian aborigine will reinforce the distinctions they would seek to minimize. How to resolve this dilemma is quickly becoming one of the most difficult problems facing the study of human genetics. (Olson, 2001)

 Skin Color to Intelligence

    His success led Cavalli-Sforza to consider the matter more broadly. If he could link genetics with mating and migrations among the people around Parma, why couldn't he do the same thing on a larger scale? In fact, he ought to be able to determine the genetic relationship between any two groups of people. A group should carry many of its predecessors' variants, just as children bear the genetic legacies of their parents. By detailing the genetic similarities and differences among groups, Cavalli-Sforza could trace humanity's spread across the planet. How modern human beings replaced their predecessors also remains a mystery. Archaeological evidence indicates that bands of modern and archaic people sometimes lived near each other for thousands of years. Yet no remnants of warfare have been found. The cave paintings of Europe, some of which date from the period when modern people were replacing Neanderthals, evince plenty of violence against animals but not against other people. More and more kinds of blood were being discovered in the 1950s. In 1961 Cavalli-Sforza decided that he had enough data to try his idea. He and a colleague analyzed published data on blood types in fifteen populations, three each from Europe, Africa, Asia, and the Americas, and one each from Australia, New Guinea, and New Zealand, and produced a tree showing how the various groups were related.

   More than 10,000 years ago, a mutation occurred in the chromosomes of man from Siberia. As one of the man's sperm cells divided, the Y chromosome in the cell underwent a copying error. One of the chemical units making up his DNA changed from a molecule called cytosine to one called thymine. An elaborate biochemical proof reading apparatus is supposed to correct such copying errors, which geneticists call mutations. But there are so many individual chemical units, or nucleotides in human DNA; about 60 million in the Y chromosome, and about three billion in the other chromosomes in a human sperm or egg cell, that a few mutations inevitably creep in every time a cell divides.  Most descriptions of evolution emphasize natural selection, in which a beneficial mutation becomes more common over time because bearers of this mutation are more likely to survive and procreate. But if an organism just happens to have lots of descendants, its genetic variants will become more common whether they are selected for or not. (Olson, 2001)

Human differences are due to culture

   Over the past decade or so genetics researchers have been undermining the widespread belief that groups of people differ genetically in character, temperament, or intelligence. They have shown that all human beings are incredibly similar genetically, much more so than other species of large mammals. They have revealed the folly of attributing group behavioural differences to biology rather than culture. Racists are convinced that human groups differ for genetic reasons in intelligence, aggressiveness, or other complex behaviours, such people have one last argument. They assume that the same forces leading to differences in appearance could somehow have influenced mental attributes. Maybe, for example, cold climates exerted some sort of selective pressure on people moving north from the tropics, favouring individuals with greater initiative or intelligence. Or maybe some other genetic process divided cognitive traits unevenly among groups.

   The argument doesn't work, for two reasons. First, no mechanism has been identified that could sort complex attributes within such a genetically homogenous species, causing the behaviour of one group to differ from that of another. The idea that natural selection favoured different cognitive traits on different continents, that selective forces on colder continents led to greater intelligence, for example, seems designed more to justify social prejudice than to establish testable hypotheses. After all, Neanderthals were much better adapted to the cold than modern human beings, yet they weren't able to compete with the newcomers from Africa and eventually became extinct.

   The best way to determine the genetic relationships among people is to compare the sequences of the nucleotides in their DNA. But in the early 1960s those sequences were inaccessible. Manipulating DNA in the laboratory at that time was not possible, existing tools were far too awkward to examine individual nucleotides. Cavalli-Sforza therefore turned to the next best thing; the many thousands of proteins in the human body. The sequence of nucleotides in DNA dictates the sequence of the amino acids that constitute proteins, though the translation between the two is a convoluted process that partially obscures the underlying DNA sequence. Still, by studying proteins Cavalli-Sforza could learn at least a little about the DNA differences among people. (Olson, 2001)

Relationship between genes and behaviors

    The complexity of the relationship between genes and behaviours will always confound simple-minded efforts to link the two. Even if a genetic variant seems to cause a particular behaviour, such as extroversion or verbal fluency in one environment, it may have no effect, or the opposite effect, in a different environment. The importance of a person's experiences makes it a fallacy to cite the frequency of certain genetic variants as the cause of group behaviours.

   The extreme interpretation of this observation, now popular in academia, is that biological groups do not exist. That's obviously absurd. The ways in which typical Nigerians, Koreans, and Norwegians differ physically belie any claim that all human groups are somehow "socially constructed." But the development of morphological differences in a widely distributed species is a biological common place. Whenever the members of a group are more likely to mate inside the group than outside, the frequency of particular genetic markers within that group can become higher or lower. In most cases these changes are entirely random, as with the blood-type distributions that Cavalli-Sforza studied in Italian villages.

But natural selection can also be a factor. To take the classic example, as modern human beings moved from equatorial regions into more-northern latitudes, dark skin was no longer needed to protect the body from the sun's ultraviolet rays, and light skin made it possible for the body to produce more vitamin D. The resultant lightening of skin colour seems to have occurred at least two times during human history; first when Africans moved north into the Middle East and then into Europe and the second time, when dark-skinned people living on the islands and mainland of Southeast Asia migrated into what is today China.  (Genetics research is demonstrating that migrations of European people into the Subcontinent of India have had much less biological significance than is commonly assumed). (Olson, 2001)

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