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Part 4: Who were the ancestors of Asians and Europeans?
Page 1: Modern Anthropological Dating Techniques
Before discussing the European and Asian ancestors, it is necessary to introduce some methodologies adopted by modern anthropology to determine dates.
Άρ.The Uncertainty of Molecular Anthropological Dating
In previous part, we discussed the Y chromosome Adam theory as well as the Mitochondrial Eve theory. Based on these theories one can extend the millennium quest with the use of DNA from modern man to trace his ancestors in the distant past. The principle behind this type of tracing and confirmation of paternal relationship is quite similar. From the standpoint of hereditary lineage, it is both accurate and error free. However, since DNA mutation is random and the mutation rate is inconstant, it is inaccurate way to determine the year of birth of our ancestors regardless of the way one uses to trace geneology i.e. via mitochondrial DNA or the Y chromosome. To get an accurate time period one needs to rely on anthropological dating techniques.
1. Estimation of the date by which mitochondria DNA haplogroup was generated
Comparatively speaking, the accuracy of dating with the mitochondrial DNA is better than dating with the Y chromosomal DNA.
To determine the exact date using mitochondrial DNA primarily depends on confirming the mutation rate. Objectively speaking, the current mutation rate are all estimates. There is a great deal of differences depending on the figures provided by various research groups. Moreover, the mutation rate of haplogroup in the past is inconsistent.
A simple technique to estimate the mitochondrial DNA’s mutation rate is this: ”You can see how many mutations have accumulated in two different groups that have been separated for a known length of time”.
To illustrate with an example: Research shows that approximately 15,000 years ago, a small group of people crossed the Bering Strait from Siberia into North America (Please see part 5). Their descendants are still living to as American Indians. Among this group, their mitochondrial DNA contains a C1b haplogroup. Those who live in present day Siberia has the C1a haplogroup. Both C1a and C1b share a common maternal haplogroup C1. The C1a haplogroup cannot be found in North America, but only in the Siberian aborigines. Likewise, C1b does not exist among the Siberian aborigines. One can, one can conclude that C1b was generated when people migrated to North America. The descendants of C1a and C1b have been separated for approximately 15,000 years.
Among these two descendants, there were 8 to 9 mutation loci among their descendants. On each hereditary line, there is on average 4 to 4.5 mutation loci. Therefore, one can estimate the each mutational period is 3,750 to 3,333 years.
The cumulative figure of mitochondrial DNA mutation loci is approximately 115 between the aborigines of Africa as compared to those in North America (Reference 1). There are 57.5 mutation loci on each hereditary line. Based on the aforementioned way to calculate mutation rate, mitochondrial Eve lived around 216,000 to 191,000 years ago. (See Figure 2-13 Mitochondrial Eve’s husband was an ancestor of Y chromosome Adam in the page3 of part 2)
2. The estimation technique to date the DNA of Y chromosome
From the previous chapter we can see that the advantage of using the Y chromosome theory to confirm genealogy is far superior than relying of fossils from archeological excavations. However, to confirm the exact date of our ancestors, there exists certain disadvantages. Such as in the confirmation of parental relationship, we can find out that Jefferson’s illegitimate son lived 200 years ago. However, we cannot determine his exact birthday from DNA analysis.
When did Y chromosome Adam actually live? From previous research on this subject, many dates were mentioned. Among these, the most cited date is 59,000 years ago. Obviously, this cannot be the correct date.
This date was mentioned in molecular anthropologist, Spencer Well’s book, “Out of Africa. The Journey of Man-A Genetic Odyssey” (Reference 2). This figure was based on the result in his research article: “Y chromosome sequence variation and the history of human populations” (Reference 3) which he had signed. However, Wells did not make the date clear in the article. However, Wells did not make it clear as to the content of the article.
Content from the original article states that” the age of the most recent common ancestor was previously estimated at 59,000 years, with a 95% probability interval of 40,000-140,000 years” Please note these words:”95% probability interval of 40,000-140,000 years. Before this publication, another date was 270,000 years ago. “A coalescence model predicts an expected time to a most recent common ancestral male lineage of 270,000 years” (Reference 4). Subsequently, another research mentioned a date of 150,000 years ( please see Figure 2-5: The Paternal genetic tree in the page3 of part 2). Why is there such a large difference among these dates?
In principle, the technique to estimate the Y chromosome era and the mitochondrial DNA era should be the same. Just by looking at the number of years separating the known haplogroups, and the accumulated numbers of mutations, one can estimate the exact date of the period.”However, mitochondrial DNA only has 16,569 DNA letters and yet, there are more than 50,000,000 DNA letters in the Y chromosome, thus complicating the estimation.
A commonly used formula for estimation is this: t = - Ne ln (1-V/ Ne μ) (reference 5) in which Ne represents effective population size , and that V is the variance of repeat numbers in the population, and that μ is the mutation rate. t is number of generations from the present ( one generation about 20 years; t multiples by 20 is the number of years from today); ln the natural logarithm symbol.
For example, to calculate the ancestors of the Han with genetic marker M122 in China, Ne identified as 750 - 2,000; μ =0.18%.Using 20 years for each generation, the result of the calculation is that 18,000 to 60,000 years ago was the date of M122’s birth. (Note: the value of V was not given in the article).
It is obvious by now that the error range is great from the results of these calculations. Just for the genetic marker’s mutation rate (μ), there is a tenfold difference among the proposed figures from different researchers. (reference 6)
In view of this, whatever dating based on the Y chromosome estimation can only be use as a reference. In this area one must still rely on the physical methods from archeology. In contrast to using the Y chromosome in dating a certain era, the margin of error is much smaller if mitochondrial DNA is used to date certain era in the past. Mitochondria Eve lived 200,000 years ago. Since this date was first proposed by Professor Allan Wilson, there is not much controversy or alteration. In different chapters within this book, the reader might find discrepancies in the dates of DNA haplogroup. We are confident that the readers will understand.
Often people ask this question: How could Y chromosome Adam and mitochondrial Eve be husband and wife if they did not live in the same time period but instead lived thousands of years apart? It was impossible for them to be husband and wife. Mitochondrial Eve was the wife of Y chromosome Adam’s great, great grandfather’s wife. Y chromosome Adam married mitochondrial Eve’s descendants many generations apart from the original mitochondrial Eve.
Άς. Traditional archaeological dating methods used in physics
1. Cabon-14 Dating Method
(1) The generation, decay and restoration of carbon-14
In nature, there are three isotopes of carbon, namely stable isotope carbon 12, carbon 13 and a radioactive isotope carbon 14. They all have six protons but different numbers of neutrons. When the neutron collides, a nitrogen-14 (seven protons, seven neutrons), they will gain a neutron and lose a proton. The atom of a nitrogen turns into a carbon-14 atom (six protons, eight neutrons) and a hydrogen atom (one proton, zero neutrons). Carbon-14 is radioactive, with a half-life of about 5,700 years.
During the growth of a plant, as it absorbs carbon dioxide during photosynthesis, it absorbs carbon 14 at the same time and retains it inside the body. After it dies, it no longer absorbs carbon dioxide and the carbon 14 in its body is no long renewed. Then, carbon 14 enters the process of decay. The decay of carbon 14 releases a beta particle (electron)so that the original neutron becomes a proton thus becoming the original nitrogen atom.
(2)The measurement of carbon 14 decay:
The range of carbon 14 dating spans several hundred thousands of years. During this period, the intensity of the cosmic ray has not changed. Therefore, the ratio of carbon 12 in the air and carbon 14 should be constant. There is just one carbon 14 atom amidst one trillion carbon atoms. When the plant dies or is eaten by an animal, the ratio of carbon 12 and carbon 14 must be “one trillion to one” in this non breathing plant. Moreover, the same ratio exists in the body of the animal. The dating of the carbon 14 half life starts from this point onward. If you find in the fossil of an ancient person the ration of carbon 12 and carbon 14 is “one trillion to 0.5”, or half of the decay half life, you can be sure that he or she lived over 5,700 years ago. In other words, he or she had died over 5,700 years ago since it is one half life.
The decay ration and time is a Natural logarithm rules. As long as this ration is not too small, one can get very accurate results. Obviously, there is one limitation, namely if the carbon14 decay cannot be measured, there is no way to determine any result with accuracy. The dating period with carbon 14 is limited to 60,000 years. With the advanced Accelerator Mass Spectrometry (AMS) radiocarbon dating method, the dating has been extended to 75,000 years.
(3) Is the carbon 14 dating method credible?
American scientist, Willard Libby first proposed the carbon 14 dating method in 1949 for which he received the 1960 Nobel Prize. Although there is still some debate as to its accuracy, but it is still a commonly accepted method by the world’s archaeological community. In the last few decades, the carbon 13 dating method has been compared with other dating methods. It has been shown to be most credible in the “calibration of the tree ring”.
Every year the tree adds one ring. Each ring retains the carbon 14 it has absorbed. The radioactive decay time starts next year. If one obtains a 5,000 year tree trunk and group it by decade with 500 sawed samples, one can find out age of the tree with the carbon 14 dating method by analyzing the carbon14 contains of each sample. Comparing the number of tree rings with these dates one can tell if there is any discrepancy and thus create the calibration curve or a calibration table to correct the carbon 14 dating data.
There are some trees which have lived for a long, long time. In the U.S., the bristlecone pine has already lived for 5,063 years. Many years ago, pine trees with thorny cones had lived over 7,000 years ago. From those dead trees with well preserved trunks, one can create the standard of the “tree ring table” by comparing the tree rings from these trunks. From North America, the “tree ring table” extends to 8,600 years and in Europe, the “tree ring table” extends to 10,000 years.
Based on these “tree ring tables”, one has extended the tree-ring vs. carbon 14 calibration extended to 11,000 years (Reference 7), even as far as 40,000 years. After calibration, the accuracy of carbon 14 dating for 10,000 year period is plus or minus 60 years error rate. For a time period of 30,000 years, the error rate is plus or minus 350 years. Between 30,000 to 40,000 years, the error rate is plus or minus 750 years. We can be certain that the carbon 14 dating method is indeed credible.
Figure 4-1 5063 year-old bristlecone pine
In the dating of some archeological articles, often two dates are given: one being the carbon 14 (C14 years before present ” C14 BP”), and the other being the calendar years (Calendar years before the present, ”Cal BP” or BP ). For example, if the age of the charred wood discovered in a cave is determined to be 12,500 (C14 BP ) and 14,5000 (Cal BP), the former is the result of carbon 14 dating and the latter is the corrected calendar years.
Some people don’t consider the carbon 14 method to be reliable. They believe that our earth and mankind only has a 10,000 year history. However, it is not consistent with scientific facts.
2. The other dating methods
(1)Uranium dating method
One of the isotopic dating methods is based on the ratio of radioactive uranium nuclides to determine the age of the geological sediments. Commonly used date methods use uranium 234U/238U, thorium-uranium 230Th/234U and thorium-lead 231Th/210Pb.
The principle of measurement is 238U and 235U decay series contain a variety of radioisotopes. In the normal geological processes, Daughter of uranium such as thorium, and lead separate themselves from parent uranium-238U and 235U. And each half-life will determine their respective rate of decay. The body of the mother forms the decay of the daughter nuclides. Radiation detectors can be used to measure the radioactive isotopes ratios in order to calculate the age of the geological sediment. If ancient mankind’s remains and relics in these sediments with the same age as the sediment, then this will represent the times when the ancient people had lived.
This method is suitable for dating the Paleolithic ancient ruins around 50,000 -600,000 years ago. Moreover, this method is limited to the determination of calcium carbonate rich rocks.
(2)Potassium-Argon Dating Method
Another isotopic dating method is to use potassium 40 which is an unstable isotope. It can decay and become argon 40. Within a stone, argon is in a liquid form and can freely escape. After the stone solidifies, potassium 40 decays to become argon 40 remaining in the stone. Using mass spectrometry instrument one can measure the argon 40 and the remaining potassium 40 ratio. From this ratio one can calculate the age of the mineral crystal and the rock containing potassium. Moreover, one can determine the age by which the rock was formed. The half-life of potassium 40 is 1.25 billion years and thus can be used to determine rocks which were formed over 100,000 years ago. More recently formed rock does not meeting the desired dating accuracy because the argon content is too low. This method is often used to determine geological events in active volcano areas.
(3)Thermoluminesense (TL) and Optically Stimulated Luminesence (OSL) Dating Methods
Thermoluminesense (TL) Dating method: Quartz crystals in feldspar, calcite, pottery, porcelain and other objects contain lattice crystal structures which can absorb radioactive electrons trapped in the lattice at a fixed rate over time. The energy in these trapped electrons can be released producing a range of luminescent glows shown as light by heating with just a small sample from the aforementioned objects.
The amount of energy can be measured by the thermoluminescence detection instrument. After subjecting to heating, certain types of electron trapping mechanism become zero. The measured amount of radiation energy is directly proportional to the age of the ceramic.
This is the principle behind the thermoluminescence as a dating method. The TL method dating range varies from several hundred years to one Millions years. Its major use is in dating burnt or heated objects. It is widely used in determining the date of archeological objects and antique such as pottery, porcelain, burnt soil in addition, flint, sedimentary soils.
Optically Stimulated Luminescence Dating
In recent years, Optically Stimulated Luminescence Dating, abbreviated OSL, was developed based on the principle from the TL dating method. Instead of heat, OSL uses an argon ion laser or xenon lamp to excite the stored energy. A more accurate date can be obtained if one compares the results from OSL and TL methods.
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£¨7£©LianZhen Chai£¬ "C14 dating ©¤ - the method for prehistoric archaeological dating.", Institute of Archaeology,Chinese Academy of Social Sciences.΅΅