All humans share a common African ancestry, making the story of Africa the story of all of us. However, little is known about the genetic evolution of the people who inhabited this continent in prehistory. Thanks to advances in genome sequencing technology, the scientific community can now compare DNA from humans living today with DNA extracted from skeletons thousands of years old, giving us a unique snapshot of life in Africa thousands and thousands of years ago.
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In the field of human genetics, the story of Eve, the universal mother, is well known. It describes how all humans alive today are descended from a woman who lived in Africa 200,000 or 300,000 years ago. The evidence comes from studies of mitochondrial DNA (mtDNA), a segment of genetic material found in human cells. Among other things, it enables the study of relationships between different populations. Since it can only be passed on by mothers, it reveals the direct line of evolution between everyone alive today and their most distant female ancestor.
mitochondrial eve
However, like most simple stories, the Mitochondrial Eve account is not entirely accurate or complete. Although the scientific community concludes that it is true that the appearance of humans took place in Africa, Eve would be just one of the many women alive at the time, and certainly not the first.
Unfortunately, the reality is that mtDNA gives us a limited view of time or patterns of population dispersal and dispersal. Mateja Hajdinjak, molecular biologist, explains what this knowledge gap means. “The history of African people has shaped the world we live in, and until we are able to reconstruct the events of Africa’s past, stretching back thousands of years, we will not be able to fully understand how humans came into being.
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Hajdinjak is a postdoctoral researcher on the ORIGIN project, an EU-funded initiative based at the Francis Crick Institute in London, UK that analyzes DNA from human remains found at archaeological sites in Africa. ORIGIN aims to reconstruct African prehistory through DNA analysis. The information from these prehistoric DNA samples will be examined alongside the finds of the project’s archaeologists, paleontologists and museum curators.
DNA extracts
Hajdinjak is one of a growing number of researchers working tirelessly to fill historical gaps by going beyond mtDNA analysis and using the latest techniques in whole genome sequencing. This allows the researchers to compare the DNA of people alive today with the DNA obtained from ancient skeletons.
“One of our fundamental goals is to find out how prehistoric DNA can be used to reconstruct the thousand-year migrations of people within Africa and from Africa to other parts of the world,” says Hajdinjak. The expert adds that little is known about the genomic landscape of prehistoric Africa, as much of the genetic change on the continent occurred when some groups abandoned their hunter-gatherer lifestyles to become farmers and herders between 3,000 and 7,000 years ago .
“By comparing genomes from the past, we can see how different human groups are connected and how migrations occurred at different periods of history. Migrations allow humans to mix and reproduce with new groups, changing human biology over time.”
Although we already have a lot of information about ancient history in Europe thanks to modern sequencing techniques, studies of prehistoric DNA from samples from Africa are lagging behind. The main reason is the degradation of DNA over time, particularly in the hot and humid climates characteristic of Africa.
genomic enrichment
The scientific community is also beginning to make remarkable advances in sequencing prehistoric DNA from Africa, thanks to state-of-the-art genome enrichment tools that make it possible to extract and amplify DNA from tiny bone or tooth fragments.
By examining the data in this way, the research staff can reconstruct ancient events and examine the relationships that emerged between different African populations.
The goal of ORIGIN is not only to satisfy our natural curiosity about where we come from, but also to decipher the timeline of our genetic evolution and use this information to predict our potential development in the future. Some genetic mutations were an immediate benefit to our African ancestors and have therefore managed to persist in the gene pool to this day, thousands of years after they first appeared. One of the most important examples is lactase persistence: the ability to digest milk in adulthood.
Milk and milk products are a valuable source of energy, but the default condition is lactose intolerance. For adults living in early African pastoralist communities, the ability to convert their herd’s milk into glucose would have given them a tremendous evolutionary advantage over lactose-intolerant groups.
Another genetic variant that, once in the genome, would have improved human survival is the sickle cell mutation. This genetic variant confers some protection against malaria. However, this mutation is a double-edged sword as it is also responsible for sickle cell anemia, a serious chronic disease that is still found in some parts of Africa.
“It would be very important to be able to reconstruct how sickle cell mutations first appeared and spread,” says Pontus Skoglund, project leader of ORIGIN. “If we can understand when these mutations occurred and how they spread, we can better understand how humans respond to the challenges of evolution,” he adds.
genetic mix
The research team at the EU-funded project AfricanNeo is particularly fascinated by early agricultural practices in Africa. They are comparing prehistoric DNA samples with contemporary DNA to clarify when African populations began migrating across the continent.
These migrations had a tremendous impact on the groups’ genetic mix, but researchers are discovering that this expansion was a complex series of events that cannot be reduced to a simplified mitochondrial Eve-style narrative.
“The spread was not uniform across the continent,” says Carina Schlebusch, associate professor of evolutionary biology at Uppsala University, Sweden, and principal investigator on the project. “Some hunter-gatherer groups were replaced by farmers and ranchers,” he explains, pointing to the likely conflicts between population groups wanting to occupy the same land and the likelihood that farmers and ranchers would have had a competitive advantage over hunter-gatherers. “Other groups interacted and exchanged genes, and others remained isolated much longer than expected.”
According to Schlebusch, the reason we should all be concerned about these complex events in prehistoric Africa is clear: “History tends to repeat itself,” he says. “These migratory events from prehistory can influence our future behavior. For example, with climate change, pressure on people forced to leave their homes is likely to increase. There is a possibility that there will be further conflicts between the populations and that some minority groups will be replaced.” And he adds: “The more we know about our history, the better we can predict how things will happen in the future .”
The research mentioned in this article was funded by the EU’s European Research Council and the Marie Skłodowska-Curie Actions (MSCA), and the article was originally published in Horizon, the European Union’s Journal of Research and Innovation.
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