It is a patchwork of extinct lakes, forests and grasslands, and is called Makgadikgadi ancient wetland. Our greatest grandmothers and grandfathers hunted, collected and raised their families for tens of thousands of years. Finally, with the change of the earth's climate, the change of rainfall has opened up a fertile new road across the desert. Our distant relatives had the opportunity to explore the unknown for the first time, leaving behind what the research team now calls "the ancestral home of all mankind today". A new paper published in Nature today (10, 18) tells us that,
By studying the genomes of more than 1200 African aborigines living in the southern part of the African continent, the research team pieced together the history of one of the oldest DNA lineages on earth: a group of genes named L0 survived in some people for hundreds of thousands of years through maternal mitochondria, but there was no obvious change. By tracking when and where the L0 lineage first split into slightly different lineages that are still seen among some African aborigines today, researchers believe that they have accurately determined where the first L0 carriers lived and multiplied for thousands of years.
"We have long known that humans originated in Africa, about 200,000 years ago," said Vanessa Hayes, a geneticist at Gavin Medical College, University of Sydney. They are all in Australia and said at a news conference that we didn't know where this country was until this study.
This "accuracy" has caused some other researchers to have doubts. Chris Stringer, an expert on human origin at the Natural History Museum in London, told Live Science that he was "cautious" about using modern gene distribution to infer where ancient humans lived10.5 million years ago, especially in a continent like Africa. Similar studies trace the earliest human groups back to different parts of East Africa, West Africa and Southern Africa. )
In addition, he added that because the current research only follows a maternal gene sequence, its findings may not capture the whole picture of the earliest human beings who crossed Africa. On the contrary, the best evidence available shows that the founders of many different genes may live in different parts of the African continent, bringing not one but several homes to modern human beings.
Just as many studies focus on a small part of the genome, a region or a stone industry, or a "key" fossil, it can't capture all the complexity of the origin of our mosaic, "stringer said. KDSP "KDSP" KDSP "KDSP" KDSP "Today, Makgadikgadi is one of the largest salt flats in the world. The climate model shows that 200,000 years ago, it was a fertile oasis. (Shutterstock)
L0 pedigree is a single DNA sequence encoded by mitochondria, which is a small structure in cells and converts food into cell energy.
Mitochondrial DNA accounts for only a small part of your genome, and most of your DNA is locked in the nucleus. However, although nuclear DNA is inherited from parents and has to be recombined in each generation, mitochondrial DNA is inherited from your mother alone and can remain unchanged for tens of thousands of years. Therefore, mitochondrial DNA (also known as mitotic genome) is a key tool to track genetic history.
L0 is particularly important in this respect, because all living people are considered to have inherited the first woman who carried the sequence, an imaginary woman called "Mitochondrial Eve". Today, the L0 lineage is the most common among the Khoisan people, two indigenous groups living in southern Africa. Many other African indigenous groups carry mitochondrial DNA, which comes from this lineage, but there are slight changes. By comparing the differences between different populations, geneticists can piece together the approximate timeline of the differentiation of these ancient genetic lineages. In this new study, researchers sequenced 200 mitotic genomes of indigenous people living in South Africa. Compared with the existing database of 65,438+0,000 L0 sequences, this data set has created one of the most comprehensive snapshots so far, and how it has dispersed the ancient pedigree and its recent branches in southern Africa today. This distribution data enabled the research team to estimate the time and place when the offspring of mitochondrial Eve first split into different groups.
"With this, we can be sure that we believe in our human home," Hayes said.
The home proposed by researchers is Makgadikgadi, a huge wetland about 46 years old, with an area of 65,438+0,000 square miles (65,438+0,200 square kilometers), which is about twice the area of Lake Victoria, the largest lake in Africa today. The research team found that mitochondrial Eve and her descendants lived in this region for about 30,000 years (from 200,000 years ago to 654,387,000 years ago) before the L0 pedigree split into the first subgroup.
"This tells us that these early humans must have stayed in the motherland, not left," Hayes said at the time.
It is a green road, so why did our ancient ancestors finally leave their homes and changed their genetic fate in the process? According to the author of this study, this may be a problem of climate change.
Using the climate model and sediment core samples in this area, the research team found that from about10.3 million years ago to 1. 1 0 million years ago, the change of rainfall pattern opened up several "green corridors" of habitable land in the desert around Makgadikgadi. The researchers write that the corridors in the northwest and southeast of wetlands may attract immigrants from these directions, thus leading them to areas where different indigenous groups still live today. This movement can fully explain the distribution of L0 subgroup in southern Africa,
But what it can't explain is the other half of our genetic pedigree (male half). According to stringer, there is not much evidence that our earliest male ancestors took the path described here.
"Looking at the Y chromosome inherited by men, the most different lineage known to mankind was found in West Africa rather than South Africa," stringer said. "The author of this study admits that modern humans may have multiple" homes "where different gene lineages take root; L0 is the best preserved lineage, thanks to its strict maternal lineage. " . Therefore, although researchers may now be closer to identifying Mitochondrial Eve's little Garden of Eden, and she started her family, it is still too early to say that we have all found our home. In the photo
The new human relatives in the photo are shaking our genealogy: the ancestors of "little feet" humans walk with Lucy Nale Dee in the photo; the photo of small headed humans was first published in Life Science magazine.
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