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Preface
The cheek swab is basically a way of getting at the DNA history book that we're carrying inside of ourselves. All of that information has to be copied in every generation, to pass on to kids, and grandkids and great-grandkids. So we're carrying this continuous, kind of genetic historic document that goes back through the generations since, you know, tens, hundreds, thousands of years ago.
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(United States, "National Geographic" TV series “The Human Family Tree”)
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To trace our ancestries, scientists have to pore through the 0.1% that's different through tiny, random changes to the As, Cs, Gs and Ts that accumulate in our genetic codes over time. Scientists call them markers. A marker is a glimpse of a person Who lived at some point in the distant past. If you share a marker with someone, you share an ancestor with the person who first had that change in their DNA.
(United States, "National Geographic" TV series “The Human Family Tree”£©
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Despite our origins in Africa, the journeys our ancestors made and the close genetic bond we all share. The differences between us all are really just superficial. We are all members of a young species that goes back less than 200,000 years, and we're all surprisingly closely related. This is the story that has emerged from the study of stones, bones and our genes. That wherever we've ended up all over the world, we are Africans under the skin.
(The Incredible Human Journey - Episode 5 - The America)
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“By analyzing sequences from living individuals, it is possible to work back to the ancestral sequence from which all the existing sequences could have sprung. This ancestral sequence represents the point at which the lineages of the living individuals coalesce into one individual, the common ancestor of them all. Then, by counting the number of mutations that occurred between the ancestral DNA sequence and the current sequences, and by dividing this number by the known mutation rate, it is possible to calculate the time that has elapsed since the common ancestor existed.” “Thus, the coalescent principle suggests that all modern humans are descended from maternal and paternal common ancestors who lived between 100,000 and 200,000 years ago. “
(Book: “Principles of Genetics” by D. Peter Snustad, Michael J. Simmons, the textbook for University of California, University of Minnesota and other seven university )
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“By tracing our ancestors through our blood and space-time tunnel, it is found that we are all offsprings of the same pair of parents 150,000 years ago, i.e. the real Adam and Eve.” (China Central Television series "Who is Eve"£©
Part one: The Era of Anthropology by DNA decoding is coming
I. The Coming of Age of DNA Decoding in Anthropology
In the mid 19th century, the nucleus was but a small black spot under the most advanced microscope at that time. When Charles Darwin’s embarked on his voyage aboard the HMS Beagle, he only had a single-lens microscope. And he proposed the Theory of Evolution based mainly on his personal observations with little help from any instrument. Moreover, with that observation, Darwin boldly introduced the idea of the origin of species and expanded that theory to include the hypothesis of human origin.
However, with the development of the electron microscope, scientists finally were able to probe deeper into the inner structure of the nucleus which turned out to be far more complex than Darwin could have ever imagined.
Back in the 1950s, high-power microscopes allowed scientists to see the nucleus of human beings containing 23 pairs of chromosomes. Thus, the first layer of mystery about the genetic information was finally uncovered. The fact that the mule, a product of the pairing of a donkey and a horse, cannot have offspring is not due to the long-held belief that its pelvis cannot “open and close” but instead due to the fact that it has an odd number set of chromosomes. A mule has 63 chromosomes in its cell nucleus, 32 from the horse and 31 the donkey. Therefore, a mule does not have the normal reproductive “machinery for breeding. It is also found that a chimpanzee has 24 chromosomes, which are not equal to the 23 pairs in human beings, an unimaginable fact for Darwin’s Theory of Evolution.
In fact, the difference in the number of chromosomes between human beings and apes irrevocably nullifies the idea of a common ancestry and the possibility that one evolved from the other. However, Darwin said: “for natural selection can act only by taking advantage of slight successive variations; she can never take a leap, but must advance by the shortest and slowest steps.” (“The Origin of Species” Chapter 6: Difficulties on Theory, by Charles Darwin)
Furthermore, “if it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.” (“The Origin of Species” Chapter 6: Difficulties on Theory by Charles Darwin)
The difference in the number of chromosomes is the unbridgeable gulf for those who propose that evolution through “slight successive variations”. One cannot buy 47.99 eggs at the supermarket. Likewise, chromosome numbers cannot exist as non-integers or fractions or decimals. Therefore, it is not possible for the chromosome number to undergo the gradual change necessary to bridge the gap between species. For example, it is not possible for 47.99, 47.98, 47.47, etc. numbers of chromosomes to exist in between 48 chromosomes (24 pairs) and 46 chromosomes (23 pairs), which is equivalent to the gradual evolution process for apes to become men.
Likewise, it is impossible for various organs with 24 pairs of chromosomes to transition into the organs with 23 pairs of chromosome via the process of evolution through “slight successive variations”. It is quite reasonable that Darwin did not know these facts. Without the power of high-power microscopes, it was not possible for him to observe that humans have 23 pairs of chromosomes whereas the ape has 24 pairs. Indeed, his Theory of Evolution faces bankruptcy in the eyes of Molecular anthropologist now.
Almost at the same time, and with the help of the high-power microscope and X-ray diffraction technique, a set of double-stranded helices (deoxyribonucleic acid or DNA) is found in each chromosome. In addition to the nucleus, the mitochondria in each eukaryotic cell also contain DNA - the mitochondrial DNA (mtDNA). Further research shows that all human genetic information is encoded in the DNA. Regardless of the massive and intricate complexity of the computer software that we use and take for granted today, the ultimate operating process is formed by “0’s” and “1’s”. The entire genetic information in human is formed by the “software”, the DNA code, containing four nucleotide base characters, i.e. Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). A person’s appearance, physical characteristics, etc. are entirely dependent on these four nucleotides DNA codes. In the final analysis, the DNA coding determines our entire physical characteristics. The same is true for every living beings.
In the 1980s, the application of DNA research into medicine helped form a new discipline called “Molecular Medicine”. At the same time, scientists began to use the genetic information contained in DNA to search for answers regarding the origin and development of mankind. At the same time, it is used to analyze the similarities and differences among various ethnic groups thus giving birth to another new discipline in anthropology called “Molecular Anthropology”.
Since then, anthropological research is no longer confined merely to our understanding of bone morphology or sole reliance on excavated fossils. Now, human beings can find answers to their origin from DNA codes.
In 1981, Dr. Fred Sanger’s group at Cambridge University for the first time published the mitochondrial genome sequence of one person of European descent. This is the famous Cambridge Reference Sequence (see Chapter 2 “In Search of the Mitochondrial Eve”). This mitochondrial genome has a length of 16,569 base pairs of DNA code containing 37 genes arranged in a circular shape of string of the DNA’s. Indeed, this discovery is truly a seminal milestone not only for Molecular Medicine but also for Molecular Anthropology.
In 1987, Professor Allan Wilson’s research team at the University of California at Berkeley found that among different ethnic groups the average difference in mitochondrial DNA mutation rate is about 0.32% (equivalent to 50 mitochondrial DNA’s alphabet). A difference even smaller than among different groups of African gorilla. Based on this seminal observation, Wilson’s group proposed the “Mitochondrial Eve Theory” that all human beings originated from one woman who live about 200,000 years ago probably in Africa (“Mitochondrial DNA and Human Evolution” Cann RI, Stoneking M, and Wilson AC Nature, 1987, 325:31-36)
In 1995, Drs. Dorit, Akashi and Gilbert published their study on a segment of the human Y chromosome, namely, the ZFY locus containing 729 base pairs. Looking for variation but to their utter amazement they found none. This seminal study formed the basis for the scientifically-proven theory of “ Y-Chromosomal Adam”. Namely, that every person on earth is a descendant of a single grand father. (Dorit RL, Akashi H, and Gilbert, W 1995: Absence of polymorphism at the ZFY locus on the human Y chromosome. Science 268: 1183-85). The era of DNA-based decoding research method has finally arrived in anthropological research.
This new theory not only shocked the entire world of anthropology but also encountered a tremendous amount of opposition. Nonetheless, by virtue of the DNA decoding in a person’s blood confirmed the close relationship among different ethnic groups as well as corrected certain misplaced ideas i.e. Peking man being the ancestor of the Chinese people, Neanderthal the ancestor of Europeans. This scientifically proven theory based on DNA decoding is irrefutably clear.
II. The direction and development of research in Molecular Anthropology
1. The goals of Molecular Anthropology research
“Molecular Anthropology” is an emerging new discipline in biological anthropology. It is a cross fertilization of biology, anthropology, archeology as well as linguistics. Primarily through the study of the human “Y chromosome”, “ mitochondrial DNA” and other genetic information, it attempts to resolve questions surrounding the origins of mankind, its interrelationships, development, structure, migration patterns among different ethnic groups, and whether or not to expect major changes in the future.
The “ Y chromosome” carries all the paternal genetic characteristics. When passed to the next generation, more than 95% of the region of DNA does not occur with maternal DNA recombination. The “ Mitochondrial DNA” carries all the maternal genetic characteristics. It is not influenced in any way by the paternal genetic characteristics when passed to the next generation. Therefore the Y-Chromosomal and Mitochondrial separately become the research targets of paternal and maternal genetic in molecular anthropology.
2.DNA Mutation Markers
With a deeper understanding of the chromosomal and mitochondrial DNA, it was noted that during the passage of DNA genetic information to the next generation there is both accurate copies as well as occasional a few mutation of individual positions on the coding of DNA base.
Why is the mitochondrial DNA a marker for the maternal inheritance? We know that the fetus is the product of the union between the mother’s egg and the father’s sperm. During fertilization, the head of the sperm containing the nucleus gets into the egg leaving the tail outside the egg. The tail of the sperm contains very little mitochondrial DNA and soon disappears. The fertilized egg contains no mitochondrial DNA from the father. Therefore, every child’s mitochondrial DNA comes exclusively from the mother. Father’s mitochondrial DNA is simply not passed to his children.
The passage of genetic information in the tens of hundreds of generations a particular locus in the mitochondrial DNA sequences may undergo mutation in a new baby girl during embryogenesis. For example, a specific DNA code’s “C” changes to another code’s “T”. At the same time she inherited her mother’s mitochondrial DNA sequences, she also possessed her own unique marker. Moreover, she can then pass along this new marker to subsequent generations through her daughter, her granddaughter, etc. This mutation-associated marker is then passed from one generation to another generation constituting a genetic network. Once scientists analyze and organize these networks, they would be able to construct a maternal genetic tree.
In fact, mitochondrial DNA genetic markers from women of ancient times are rarely seen. If there is a generation in which there is no daughter, then this mother’s genetic markers are lost. Through inheritance, the mitochondrial DNA markers form many combinations in modern man. There are approximately over 2,000 large ethnic groups on earth based on the maternal genetic tree classification. Studies have shown that the difference between our mitochondrial DNA and the original Eve’s mitochondrial DNA sequence is just a few dozen mutations. The rest of the more than sixteen thousand sites on the mitochondrial DNA is the same as Eve’s mitochondrial DNA.
The Y chromosome record the paternal genetic markers which is generally comparable to that of the maternal genetic markers on mitochondrial DNA. Molecular anthropology is founded on research conducted on these two types of genetic markers.
Just a few years ago, the Human Genome Project was completed. It is a monumental achievement and remains the largest international collaborative scientific research project to date. The term “genome” does not mean “ the combination of human genes” but instead the entire sequence of base pairs contained within the human chromosomal DNA i.e. 3.1 billion base pairs and their combinations. At this time, there are more than 20,000 genes which only account for about 3% of the entire DNA region, the rest of the DNA (97%) resides on the so-called “desert (garbage or unknown area)” of the human chromosome.
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Molecular anthropology primarily conducts research on the mutation markers residing on the Y chromosome and mitochondria. Even though these mutation markers can occur anywhere - most of the cases, they occur on the “desert” region of the Y chromosome. Imagine a highway across a huge desert. Even though there are people living in nearby small towns, but the majority of the vast area is largely uninhabited desert. Since 97% of the genetic markers which, like sign posts, reside in the DNA “desert” area, this becomes the most important region to record the “DNA-related historical archives” of mankind. Looking at the “desert” region of the human DNA is no longer viewed upon as the “garbage region”. Meanwhile, this region also contains the information of control commands and the non-physical genetic information. These are all important factors to generate an intelligent individual.
Molecular medicine is the study of “inhabited towns”. Molecular Anthropology is the study of the sign posts on the highway.. Regardless whether there are people living nearby, the sign posts are always there. “Cities” or “towns” are where the specific genes reside. Molecular biology and molecular medicine are only interested in genes because researchers’ current view is that only genetic information is relevant for man’s physiological processes.
We will also describe in detail the above contents in the next part of the discussion.
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