Origins analysis with DNA genealogyWho were our ancestors? From where do we originate? Most people can trace their family tree back no further than three or four generations. Thanks to genetic analysis, however, it is possible to look back into millennia long past.
"Home is not a geographic concept, but something we all carry inside ourselves." A.D. Sinjawsky
The story of our ancestors is probably one of the most exciting of all time. It is the story of mankind. For decades the only evidence available to anthropologists and archaeologists were the small amount of bones and objects left behind by our ancestors. Hence, it was not possible to really prove the various theories of evolution. It is only in the past 20 years that researchers have been able to use the DNA of living people as a means of finding evidence of the migrations of their primeval ancestors.
DNA is identical to a degree of 99.9 percent for all people. The remaining 0.1% is the source of individual differences (such as eye colour, certain risks of disease, or deviations with no apparent function). Once in each evolutionary period a harmless, random change in the DNA (mutation) can occur in the section of DNA with no function; this change is passed on to all descendants of the respective person. If the same mutation appears generations later in the DNA of two people, it is clear they have a common ancestor. The comparison of certain sections of DNA (marker genes) in many different population groups makes it possible to trace relationships.
The largest part of the genome is repeatedly mixed by the combination of DNA from the mother and father. However, this is not the case in two areas of the genome:
Mitochondrial DNA (mtDNA): the mtDNA is passed on from the mother to her child intact. Every person - whether man or woman - inherits his/her mtDNA only from his/her mother.
Y chromosome: the Y chromosome is passed on unchanged from father to son. Each man receives his Y chromosome exclusively from his father.
A comparison of the mitochondrial DNA and Y chromosomes of people of different groups of the population gives geneticists an idea of when and where these groups separated whilst migrating around the world. For example, if one compares the Y chromosome between Europeans and Australian Aborigines, one finds distinctive differences: the male Aborigines often carry a Y chromosome with a very specific pattern in a section of DNA. This marker (M130) is not found in Europeans, however, the M89 marker is very common, which is in turn not found in Aborigines. In contrast, the M168 marker can be found in both groups of people. Evidently, Europeans and Aborigines have a common male ancestor from whom the M168 marker comes. His descendants, however, eventually went their separate ways: one group settled in Southeast Asia and Australia and in the course of time the other came to Europe. After contact between the groups came to an end further random mutations occurred, these were passed on from generation to generation and can now only be detected in one of the two groups.
According to the "Out-of-Africa" theory, the story of mankind begins in Africa. It was from there that Homo erectus populated Asia and Europe at least 1.75 million years ago. Various human forms evolved locally from Homo erectus, such as the Neanderthals. A maximum of 100,000 years ago another, new form of man began to populate the world: the Homo sapiens sapiens, which originated in Africa approximately 200,000 years ago. This was the beginning of the story of modern man. The migrant group of hunter gatherers consisted of no more than a few hundred people, from whom 200,000 years later over 6.5 billion descendants - the current population of earth - have emerged. Archaeological discoveries as well as anthropological skull studies and the latest findings of DNA research confirm the "Out of Africa" theory.
Between the original Homo sapiens sapiens and today's modern man are millennia of struggling for survival, migration as well as isolation, and conquest. Most of the details remain unknown to this day. What is certain is that these people left their home continent in order to populate the whole world. What moved them to emigrate from Africa 50,000 to 70,000 years ago? Who were the first modern humans in Africa? In short: where do we come from?
Approximately 50,000 to 70,000 years ago a small group of Africans travelled to western Asia. All non-Africans have specific DNA variants, which also characterised these first emigrants. Some archaeologists are of the view that the emigration was related to a cultural revolution, which encompassed better tools, larger social networks, works of art, and body jewellery. During the migration to Asia two paths were open to them. One led up the Nile Valley, then across the Sinai Peninsula and north into the Levant; the second was with boats along the southern coastline of the Red Sea to Arabia. When the last ice age began 70,000 years ago, the sea level dropped. Hence, the width of waterways then will have barely exceeded a few kilometres.
Genetic traces indicate that after arrival in Asia the group the split. One remained in the Middle East, the other moved along the coasts of the Arabian Peninsula to India and further east. Each generation probably only advanced a few kilometres, making it more a few steps along the beach than a migration. 45,000 years ago these people reached Southeast Australia. Sometime during this period a man was buried at a place we now refer to as Lake Mungo. Researchers found objects in the layers of earth below the grave; these could be up to 50,000 years old. These objects represent the oldest evidence of humans far beyond Africa. There is no visible evidence of early humans in the 13,000 kilometres that stretches between Africa and Australia. These can probably no longer be found due to the rise in sea level after the end of the ice age. However, a genetic trail was preserved: an indigenous population on the Andaman Island group off the coast of Myanmar, Malaysia and in Papua New Guinea demonstrates signs of an old mitochondrial lineage left by early migrants.
People in the rest of Asia and Europe have different but equally primeval mtDNA and Y chromosome lines of ancestry. They indicate the origin of the second, slower developing branch of the African emigration. Initial progress was delayed due to impassable terrain and the climate of the ice age. Neanderthals, the descendants of much earlier pre-modern man from Africa, also lived in Europe. Approximately 40,000 years ago Homo sapiens sapiens eventually arrived in the land occupied by the Neanderthals. In the Le Conte cave in France items of the Neanderthals and early modern humans in adjoining layers of earth indicate that these two groups may have met; the way they interacted with one another remains a secret to this day. We know only that modern man, who had far better tools available, increasingly displaced the Neanderthals until they finally became extinct. According to previous findings, the two groups had no common descendants.
At around the time when modern humans arrived in Europe, members of the same group from the Middle East spread into Central Asia. About 40,000 years ago, they reached southern Siberia. Population groups went different ways, in the process their lines of ancestry branched out. Some groups lived in isolation, but not completely segregated.
The DNA of living Native Americans can be used to clarify certain controversies. Most have DNA variants that connect them with Asia - the same genes are frequently found in humans from the Altay region of southern Siberia. In this case, migration possibly began via the Bering Strait. So far, there is no genetic evidence to suggest whether North and South America was populated by one single early movement or in two or three waves. The time frame is also difficult to determine: 15,000 to 20,000 years ago. The first Americans probably moved down the coast from one piece of fertile land to the next, always between the cold sea and towering ice wall. In the Americas, man had populated most of the world.
Primal mother Eve, primal father Adam
In the mid-eighties geneticist Allan Wilson from the University of California determined where the first people came from with the help of mitochondrial DNA. The comparison of this part of the genome led to the recognition that the variety of DNA variants in women of African origin is twice as wide as that of the female population elsewhere. Due to the fact that the mutations occur at regular intervals, he concluded that Homo sapiens sapiens lived twice as long in Africa as in other parts of the world.
Researchers now assume that all people are related to one single woman: the "mitochondrial Eve". She lived approximately 150,000 years ago in Africa and was certainly not the only woman of that time. However, analysis of our genes shows that the whole of humanity descends from this woman via an unbroken chain of mothers. By analogy to mitochondrial Eve, there exists "Y chromosome Adam", the primal father of all of us. He also came from Africa. Increasingly precise DNA studies have repeatedly confirmed this chapter of our history: all people of the world, no matter what skin colour, originate from African hunter gatherers.
Differences as a result of copying errors
Each cell of our body contains a copy of our DNA. Whenever a cell divides itself, it has to copy its DNA so that each daughter cell contains the complete DNA. This is a very precise process. However, it is not perfect. For example, if the mtDNA is copied and packed into an ovum, the mitochondrial nucleotide sequence almost always corresponds exactly with those in the other cells of the mother. However, occasionally errors occur. A DNA block (nucleotide) is swapped, e.g. a G instead of an A. DNA copying errors of this nature are called mutations.
Mutations are the key to the reconstruction of our genetic history. By way of example, let's assume that mitochondrial Eve had two daughters, one of whom happened to have one single mutation in her mitochondrial DNA. All women living today who descended from this daughter would have this mutation, while all women from the other daughter would not. Thus, mitochondrial Eve would have created two different mitochondrial lineages (haplogroups). The two different mitochondrial DNA sequences are referred to as haplotype.
Haplotypes and haplogroups are like a record of family ancestry, from which geneticists can identify relationships. The DNA ring contained in the mitochondria is so small that mutations rarely occur. The DNA sequences of our chromosomes are 40,000 times longer than those of our mitochondria.
Along with the mutations inherited from their parents, as they grow people reproduce new mutations in their sperm or ova, which account for the genetic uniqueness of the next generation. Hence, each generation supplements the inherited DNA with new mutations. The result is a complex genealogy, a tricky, segmented tree of genetic alterations.