This article by Razib Khan appeared in London’s Telegraph. See also our November 15 post, A History of Slavery and Genocide Is Hidden in Modern DNA, for more on the subject.
Over the past century history has been approached from many different angles, despite the stereotype of scholars haunting dusty archives. Adventurers once called antiquarians became archaeologists, and inspired the fictional Indiana Jones. Today it is the turn of the geneticists to put their stamp upon history. By tracing patterns of variation they gain insights as to the shape of the past.
Here’s an example. Every schoolboy knows that the “history” of the Caribbean region of North America began in 1492, but the authors of a new paper in PLoS GENETICS add some twists to the story.
In the 16th century there was a massive cultural and demographic transformation across the the Antilles, from Cuba down to Trinidad. Where on the mainland the indigenous populations were oppressed, the peoples of the Caribbean islands vanished. Yet the modern peoples of the Antilles, of European and African ancestry, have oral histories of descent from groups such as the Taino who met Columbus.
Historians and anthropologists have dismissed these claims. They point out that assertions of indigenous ancestry by Caribbean peoples might be a way to obscure their African ancestry, which connects them to thefraught history of slavery. Scholars whose stock in trade involves describing and explaining patterns of culture presumed that the recollections of Amerindian ancestry were products of cultural forces.
Today this question can be resolved by graphs. In figure 1 panel B of the aforementioned paper you can see a pattern which has been found many times over the past 10 years: some Dominicans, and most Puerto Ricans, are shifted toward Amerindians in charts representing genetic distance.
Case closed. The historians and anthropologists who argued that the peoples of the Caribbean were concocting their own ancestries were the ones creating fictions to lend support to their own preconceptions. On the other hand, the textual evidence does indicate an evisceration of indigenous society with the arrival of Europeans and Africans.
Science can give an answer which resolves this seeming contradiction. To understand how, we need to go back to basic genetics.
An individual inherits two chromosomes, one from their father, and one from their mother, as a product of fertilisation. These single chromosomes are not simply copies, they mix and matches of segments of the grandparents’ chromosomes. This shuffling, recombination, means that your ancestry along a sequence of DNA alternates between segments inherited from different ancestors. A region inherited from your maternal grandfather might be followed by one from your maternal grandmother. The length of these sequences is dependent on the number of shuffling events, which occurs once ever generation. The more generations, and the more shuffling of segments from ancestors.
What does all of this have to do with Amerindian ancestry in the Caribbean? The researchers found that segments of Amerindian ancestry are very short and of relatively even size. The shortness of the segments of Amerindian DNA means that there must have been many generations of shuffling to break apart the long sequences. The uniform size of the segments means that they were mixed into the ancestral gene pool at the same time, approximately 1600 AD. After this the mixing ended. There was demographic extinction, just as the historians record. But that extinction was not genetically total.
And who were these people? It seems likely that they were women. Women have two X chromosomes, and men have one. Therefore, about two thirds of the time X chromosomes are present in females, so their history is more representative of one’s female ancestors. Amerindian ancestry seems to be elevated on the X chromosome in comparison to the rest of the genome.
This leads us to a stark conclusion. The Spanish who arrived in the New World were de facto polygamists who killed or enslaved the local men and impregnated the women. The broader social and cultural patterns which have long been known by history and legend are being given crisp definition by genetic science. Genetics not only tells a more complex past, but it helps paints a truer picture.
For the original report go to http://blogs.telegraph.co.uk/news/razibkhan/100248977/how-genetics-are-rewriting-the-history-of-the-caribbean/