Who were our ancestors? Where do we come from? Most people can trace their family tree back for no more than three or four generations. Thanks to the genome analysis, however, it is possible to take a look into the past millennia.
Home is not a geographic term, everyone carries it in. A.D. Sinjawsky
The story of our ancestors is probably one of the most exciting of all time. It is the history of humanity. For decades, the few bones and objects that left our ancestors on their paths provided the only clues for anthropologists and archaeologists. So the different theories of evolution could not really be proved. Only in the past 20 years, the researchers have discovered in the DNA of living humans evidence of the migrations of their ancestors in prehistoric times.
DNA is 99.9 percent identical in all humans. The remaining 0.1% is the cause of individual differences (e.g., eye color, certain disease risks, or variances with no apparent function). For all evolutionary periods, there may be a random, harmless change in the DNA (mutation) in these dysfunctional sections of DNA, which will be passed on to all descendants of the individual. When the same mutation appears in the DNA of two people for generations, it is clear that they have a common ancestor. The comparison of certain DNA segments (marker genes) in many different population communities makes it possible to trace kinship connections.
Most of the genetic material is repeatedly mixed by the combination of DNA from mother and father. But this is not the case in two areas of the genome:
In mitochondrial DNA (mtDNA): The mtDNA is inherited intact from the mother to the child. Every human being – man or woman – inherits his mtDNA exclusively from his mother
In the Y chromosome: The Y chromosome is passed on unchanged from father to son. every man gets his Y chromosome exclusively from his father.
A comparison of mtDNA and Y chromosomes in people from different strata of the population gives geneticists an idea of when and where these groups split up in the migrations around the world. For example, comparing the Y chromosomes between Europeans and Australian Aborigines reveals characteristic differences: the male Aborigines often carry a Y chromosome with a specific pattern at one side of the DNA. This marker with the designation M130 is not found in Europeans, but very often another named M89, which again does not exist among the Aborigines. The marker M168, however, can be found in both groups of humans. Obviously, there was a common male ancestor of Europeans and Aborigines, from whom comes the marker M168. However, his descendants eventually went their separate ways: the one populated Southeast Asia and Australia, the other came to Europe over time. After contact between groups ended, random mutations were inherited that were inherited from generation to generation and today can only be detected in one of the two populations.
“Out-of-Africa”
According to the “Out-of-Africa” theory, humanity originated in Africa. From there, Homo erectus set up at least 1.75 million years ago and populated Asia and Europe. From him developed locally different human forms such. the Neanderthal man. At least 100,000 years ago, another new human being set off to subdue the earth: Homo sapiens sapiens, which originated in Africa about 200,000 years ago. This is where the history of modern man begins. The emigrated group of hunter-gatherers totaled no more than a few hundred people, but over 200,000 years later more than 6.5 billion descendants emerged from it: today’s population of the earth. Both archaeological findings, as well as anthropological skull examinations and the latest findings of DNA research, confirm the “out-of-Africa” theory.
Between the original Homo sapiens and today’s modern man are millennia of struggle for survival, migration, isolation, and conquest. Most of the details are still unknown. What is certain is that these people have left their home continent to settle the whole world. What moved them to emigrate from Africa 70’000 to 50’000 years ago? Who were the first modern humans in Africa? In short: Where do we come from?
The Hike
About 70’000 to 50’000 years ago a small group of Africans wandered over to western Asia. All non-Africans have special DNA variants, which also marked these first emigrants. Some archaeologists believe emigration is correlated with a cultural revolution that included better tools, larger social networks, art and body jewelry. On the hike to Asia, they had two paths open. One led up the Nile Valley, then across the Sinai Peninsula and north to the Levant; the second with boats across the southern foothills of the Red Sea to Arabia. When the last ice age began 70,000 years ago, the sea level dropped. At that time, the waterway would have been barely more than a few kilometers wide.
Genetic traces indicate that the group split up after arrival in Asia. One remained in the Middle East, the other moved along the coasts around the Arabian Peninsula to India and further east. It is possible that each generation only penetrated a few miles at a time, so it was less walking than a few steps along the beach. 45,000 years ago, people reached the southeast of Australia. At some point during this time, a man was buried there at a place we call Lake Mungo today. Under the grave, researchers found objects in layers of earth, which can be up to 50,000 years old. They are the oldest evidence for people far beyond Africa. On the 13,000 kilometers between Africa and Australia, there are no visible signs of the early humans. They may not be found due to sea level rise after the end of the Ice Age. But one genetic trace has been preserved: an indigenous population in the Andaman Islands off the coast of Myanmar, Malaysia and Papua New Guinea show signs of an ancient mitochondrial lineage left behind by early migrants.
People in the rest of Asia and Europe have other, but also primeval mtDNA and Y chromosome lineages. They point to the origin of the second, slower branch of African emigration. Initially, rough terrain and the glacial climate delayed its progress. In Europe also lived the Neanderthals, descendants of much earlier, premodern African people. About 40’000 years ago, the Homo sapiens sapiens finally penetrated into the land of the Neanderthals. In the Le Conte Cave in France, objects of the Neanderthals and early modern humans in superimposed layers of the earth suggest that the two human species may have met together. How they dealt with each other is still a big secret.
One only knows that the modern man, who had far better tools, repressed the Neanderthals more and more until at some point they were completely dead. Recent research shows that modern humans and Neanderthals had common offspring. On all continents except Africa, today’s humans have a Neanderthal DNA content of up to 5%. It is therefore assumed that modern man has met the Neanderthals on his migration in the Middle East, where the two groups have been mixed up.
Around the time the modern man came to Europe, members of the same group spread from the Middle East to Central Asia. About 40’000 years ago they reached southern Siberia. Populations went different ways, and so branched out their genetic lineages. Some groups lived isolated but not completely isolated.
The DNA of living native Americans can help resolve some controversy. Most of them have DNA variants that link them to Asia – the same genes are found in people living in the Altai region of southern Siberia. Maybe the hike started over the Bering Strait here. So far there are no genetic clues as to whether North and South America were colonized in a single previous movement or in two or three waves. The timeframe is also vague: 15,000 or 20,000 years ago. The first Americans were probably moving down the coast to move from one piece of food land to another, always between the cold sea and the towering ice wall. With the American double continent, humans had colonized most of the earth.
First mother Eva, forefather Adam
In the mid-1980s, the geneticist Allan Wilson of the University of California used mitochondrial DNA to determine where the first humans came from. The comparison of this part of the genetic material led to the realization that women of African descent have twice the diversity of DNA variants as the female population elsewhere. Because 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 today assume that all humans are related to a single woman: the “mitochondrial Eve”. She lived in Africa about 150,000 years ago and was certainly not the only woman back then. But the analysis of our genes shows that all humanity is descended from this woman through an unbroken chain of mothers. For mitochondrial Eve there is analogous to the “Y chromosome Adam”, our forefather. He comes from Africa too. Increasingly detailed DNA studies have repeatedly confirmed this initial chapter of our story: All human beings of the earth, no matter what skin color, derive their origin from African hunters and gatherers.
Copy errors make differences
Each of our body cells contains a copy of our DNA. Whenever a cell divides, it has to copy its DNA so that every daughter cell gets the complete DNA again. This process works very well. Nevertheless, this process is not perfect. If e.g. When the mtDNA is copied and packed into an egg, the mitochondrial nucleotide sequence in the egg is almost always the same as in the other cells of the mother. Occasionally, however, there is a mistake. A DNA building block (nucleotide) is e.g. is disturbed, and instead of an A there may be a G. Any such error in copying the DNA is called a mutation.
Such mutations are the key to the reconstruction of our genetic history. Suppose that mitochondrial Eve had two daughters, one of which happened to have a single mutation in their mitochondrial DNA. All the women living today who are descendants of this daughter would have this mutation, while all the women who were descended from the other daughter would not wear this mutation. The mitochondrial Eve would have produced two different mitochondrial lineages (haplogroups). The two different mitochondrial DNA sequences are called a haplotype.
Haplotypes and haplogroups are like pedigrees that let the geneticist know who is related to whom. The mitochondrial DNA ring is so small that mutations are rare. The DNA sequences of our chromosomes are 40,000 times longer than our mitochondria.
As people grow up, the mutations inherited from their parents reproduce in their sperm or egg cells, along with new mutations that make up the genetic uniqueness of the next generation. Each generation shapes the DNA that it inherited with new mutations. The result is a complex genealogy, a twisted family tree of genetic modification.
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