There are many ways of reconstructing the past. You can look at documents, from dusty old photographs to beautifully crafted texts from previous millennia. Or you can study archaeological sites, with their fragments of pottery, bronze artefacts and the bones of the dead.
You could even look at the present, to see what modern languages and traditions can tell you about how ancient populations spread and interacted.
Or you could look at genes. In a groundbreaking study, published in the US journal Science, geneticists in Germany and Britain have become the first to use their field to show how human populations mixed with one another in the past and when this happened.
Using techniques that can offer evidence of events as far back as 4,000 years, the scientists have looked at 95 groups of people around the world, including the UAE population.
By analysing variation between individuals and populations, they have detected that genes from groups related to the Bantu people of East or South Africa, and with similarities to some populations in West Africa, arrived in what is now the UAE in about the year 1754.
The genetic data indicates that this “admixture” event, thought to be the result of the long-abolished Arab slave trade, could have begun as early as the mid-17th century, and may have continued into the first half of the 19th century.
It was not the first such “admixture”event. An earlier one, from sub-Saharan Africa, appears to have happened about 1,200 to 1,300 years ago. That far back, though, it is much harder to say from where, or when, the genes arrived. Although then, the new arrivals also had genetic similarities to the Bantu people.
Daniel Falush, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and one of the study’s lead authors, suggests that while his research does not pin down an exact source for the older event, it could be from the same area as the more recent one.
That, he says, “would be consistent without our analysis of other nearby populations”.
It is also unclear whether the admixture events were sudden, or took place over long periods, but what is clear is that the genetic data ties in with historical evidence of the transfer of people from sub-Saharan Africa into the Arabian Peninsula about these times.
The researchers studied variation in the genetic code at almost half a million sites on the chromosomes, the structures in the nuclei of cells that contain the genetic material of 1,490 people.
Looking at the 22 pairs of chromosomes (excluding the X and Y chromosomes that determine sex), they searched for similarities between the chromosomes of different groups to highlight mixing events.
With more recent admixture, matching sections within chromosomes tend to be longer than if the mixing took place further back.
This is because, through a process called crossing over, chromosomes within a pair exchange sections with one another down the generations, breaking up stretches of DNA over time. So the lengths of shared stretches of DNA give an approximate date for admixing.
When it comes to the UAE population, the researchers found genetic resemblances to Saudi Arabians, Jordanians, Bedouin, Iranians, Syrians, Pathans and Cypriots, among others.
That there are similarities with at least a dozen other groups suggests that the UAE population, excluding the Bantu admixture, is not very similar to any one of the other populations in the sample, says Dr Falush.
But the small sample sizes – only nine Emiratis were included in the study – and the fact that the method is better at showing up recent rather than old admixtures, plus mixing events between distinct populations instead of similar ones, make it difficult to determine the relationships between the UAE population and other groups in and around the Middle East.
“It might be a mix involving some of these groups, but the analysis is also consistent with it having a long, independent history,” says Dr Falush. “It is not very surprising to me that [the study] just tells a story about African admixture [with the UAE population], because the largest differences in genetic make-up are between sub-Saharan Africa and the rest of the world.”
It is not just the UAE population that has evidence of African admixture. The study found that 17 populations from and around the Arabian Peninsula and the Mediterranean, including North Africa, show evidence of genes originating from populations in sub-Saharan Africa.
For groups from close to the Arabian Sea, the sources were East or South African, while with the Mediterranean populations the genes came from West Africa.
The Arab slave trade is just one of many chapters in world history highlighted in the study.
The 13th-century expansion of the Mongol empire is “geographically broad and easy to identify”, according to the researchers, appearing as “a particularly abrupt transfer of people and DNA across Asia”.
Historical evidence suggests it took, for example, just a handful of years for Genghis Khan to add Persia, much of India and northern China to his empire, so if the Mongols had children with the populations they conquered, the transfer would certainly have been abrupt.
The influence of the European slave trade, in which people from West Africa were forcibly taken to the Americas, also shows up.
As a follow-up to the project, the researchers are contributing to the “Peopling of the British Isles Project”, which will try to understand the myriad genetic influences that closely related European populations had on the people of the UK.
“Larger numbers of samples, especially if they are carefully collected from different regions and groups, could allow a much richer story to be told,” says Dr Falush.
This project will probably offer a tantalising glimpse of what might be revealed by a similarly detailed genetic analysis of the people of the Middle East.
