The most comprehensive human family tree ever created
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By combining thousands of modern and ancient genomes, British scientists have succeeded in building the most comprehensive human family tree to date which shows how individuals across the world and the times are linked to each other with unprecedented precision. Explanations.
Since the announcement of the sequencing of the human genome in 2000, millions of individual sequences, including those of thousands of prehistoric humans, have been performed.
Modern and ancient genomes are invaluable tools that have dramatically improved our understanding of human evolution and the long history of people on Earth, say the authors, whose work is published in the journal Science in a statement ( in English).
This mountain of data somehow contains the history of Homo sapiens. However, it is difficult for scientists to paint a complete picture of the genealogy of the species because of the different methods of obtaining these data, their variable quality and the inherent limits of their analyzes in particular the ;Ancient DNA.View larger
Visualization of human ancestral lines in time and space. Each line represents an ancestor-descendant relationship in the genealogy of modern and ancient genomes. The width of a line corresponds to the number of times the relationship is observed, and the lines are colored according to the estimated age of the ancestor.
Population geneticist Anthony Wohns and his colleagues at the Big Data Institute at the University of Oxford, UK, claim to have succeeded. They created the most accurate human family tree to date from over 3600 high-quality modern and ancient genomes from over 215 different human populations.
In this large sample, they identified 6,412,717 variants. It is small genetic differences between individuals that make it possible to connect each of them and to pinpoint the time and place of their emergence. To refine this analysis, the researchers also relied on the examination of 3589 other ancient genomes of lesser quality which did not however end up in the family tree.
These ancient genomes, three of which were from Neanderthals and one from Denisovan, included samples ranging in age from several thousand years to over 100,000 years. Algorithms predicted where common ancestors were located in the evolutionary tree to explain patterns of genetic variation.
The resulting tree structure tells the story of the humanity over 2 million years: it contains no less than 27 million ancestors and its branches include 231 million ancestral lines linking genomes in time.
“We basically built a huge family tree, a human genealogy. […] This genealogy allows us to see how the genetic sequence of each person is linked to all the others, at all points of the genome.
— Yan Wong, Evolutionary Geneticist at the Big Data Institute
Furthermore, the researchers say their work helps paint a chronological and geographical portrait of major events in the x27;human history, including migration out of Africa.
This work represents an important step towards mapping the full range of genetic relationships between humans. Researchers believe that it may one day be possible to trace the ancestry of each of us.
Since individual genomic regions are inherited from only one parent, either the mother or the father, the ancestry of each point in the genome can be considered a tree. Calculating all of these trees, called an ancestral recombination graph, makes it possible to link genetic regions over time and trace back to the ancestors where the genetic variation first appeared, the researchers explain.
“We are essentially reconstructing the genomes of our ancestors and using them to form a vast network of relationships. We can then estimate when and where these ancestors lived. The power of our approach is that it makes very few assumptions about the underlying data and can also include modern and ancient DNA samples.
—Anthony Wilder Wohns
This study lays the groundwork for the next generation of DNA sequencing. As the quality of genomic sequences from modern and ancient DNA samples improves, trees will become even more accurate. We will then be able to generate a single, unified map that explains the origin of all the human genetic variations we observe today, concludes Professor Yan Wong.
The power and resolution of tree ancestral recombination techniques promise to help clarify the evolutionary history of humans and other species, write researchers Jasmin Rees and Aida Andrés in a paper by analysis accompanying the study. It is likely that the most powerful means of inferring evolutionary history in the future will have their foundations firmly established in these methods, they continue.
The technique is also valid for most living species, from orangutans to bacteria. In addition, it could possibly be used in the field of medical research, for example by identifying genetic predictors of the risk of a disease.