by Kemosave » March 22nd, 2005, 8:24 pm
Some info from another post for you. I will be happy to provide the scientific citations for my assertions. I ask that you do the same:
"What is becoming of chief interest for a number of anthropologists is molecular anthropology or the use of genetic information among living human population groups today to extract an understanding of humanity's origins. And from similarities and differences in gene sequences and by looking at the extent of those differences we can get an understanding of the date of humanity's origin, the location of humanity's origin, the original population size, and the pattern of humanity's spread.
The principles behind this are relatively easy to understand. The differences in gene sequences among human beings is due to mutations.
These mutations presumably can accrue at a constant rate if the region of DNA is not under the influence of natural selection. This is called the molecular clock hypothesis.
Therefore if two populations separate from an ancestral population, they are going to be different over time due to these mutations. The greater the number of mutations the greater amount of time they separated from the ancestral population.
By looking at the pattern of similarities and differences with respect to a large number of populations we can begin to identify how population groups relate to each other in this ancestral descendent fashion and then we can work backwards using this molecular clock approach to a date for the first human population.
The principle is simple but the mathematical modeling behind it is rather complex. This is but one in an ensemble of modern techniques that are being applied to molecular anthropology.
For example, in the case of genetic diversity, what is startling about humanity's genetic diversity is how limited is. In fact, the genetic diversity among humans (even though we are a global species) is the most limited of any species we are aware of. In fact, the genetic diversity of the entire human population is about a factor of six times less than a single tribe of mountain gorillas.
Which means that humanity must have a recent origin because the diversities due to mutations show there hasn't been a lot of time for these mutations to accrue but not only that humanity must have had a recent origin from a small number of individuals that quickly expanded to fill the globe. Now the origin of humanity is typically placed in Africa in the region of East Africa.
Now while genetic diversity is one of the first techniques applied to the question of human origins, it is now being applied as a technique with respect to the question of human origins as a result of the human genome project.
There is a program being launched where the goal is to characterize the genetic diversity within the entire human genome for representatives of different population groups with the idea that this understanding is going to help identify where there are defective genes that correlate with the onset of certain genetic disorders. As a result, it has become recognized that the genetic diversity among humanity is extremely limited and though the genetic diversity is potentially quite large because of the large population of the entire human population group, which again reinforces the results that humanity had a recent origin with a small number of individuals that expanded rapidly.
Now mitochondrial DNA (bean shaped cells found in our body involved in energy production) to date the origin of humanity. The reason this is done is because the mitochondrial DNA in our body comes exclusively from the maternal lineage (very clean inheritance). Using this technique, humanity dates about 150,000 years ago to a small number of women to a single woman in East Africa (called mitochondrial Eve).
Now in calibrating the molecular clock we find the clock is not as fine tuned as we would like it to be. Examples would be some parts of the mitochondrial DNA are operating under the influence of natural selection and no longer legitimate molecular clocks and radiation in the environment that varies can influence mutation rates. So while we know the approximate date of the origin of humanity within parameters, the exact date must be taken with a grain of salt as they say.
Another technique is y chromosomal analysis tracing the paternal lineage (i.e. men) and gives results very similar results as the mitochondrial method. This method shows that humanity originates under 150,000 years ago to a small population of men to a single individual male (called Y chromosal Adam). Microchondrial DNA supports this. Pseudo genes, show qualitively the same thing. So do other methods and studies give similar results.
Parasites, like body lice for example, that affect humans are now being studied as well and their origins date less than 150,000 years ago (body lice less than 70,000 years ago from a single location and again show a spread from near the Middle East). And again all of these, within the limitations of the individual techniques, all show the same result: A recent origin of humanity from a single location from a small population of men and women and humanity is traceable back to a single man and a single woman. Definitely these studies provide a powerful confirmation in the broad sense of humanity's origin.
Peace.