Good morning everyone, its a great honour to be here today to talk - PDF document

Good morning everyone, it’s a great honour to be here today to talk about our research project. My name is Gil Bellis , I’m a demographic researcher at INED, Paris. I’m working in collaboration with Jean-Michel Dugoujon and other collaborators to reconstruct the demographic history of African-descendant populations in South America. 1

Here the outline of my talk. I’m going to give you a little background information about the transatlantic slave trade, and the impact of this important movement of people. Then, I’m going to talk you about some of the challenges to use genetic markers in order to shed new light in historical and demographic studies. Finally, I’m going to present our last study of African-descendant Maroon population from French Guiana and Suriname, which is going to be publish in the next issue of the American Journal of Human Genetics. 2

Around 12 million Africans were forced to move to the New World, especially in different ex-European colonies in South America, such as Brazil, Colombia, and French Guiana. Thanks to historical information, we know the African embarkation ports of most of the enslaved Africans. However, their geographical origin far inland in the continent remains unclear. Most of the enslaved Africans escaped captivity and formed communities of runaway Africans throughout the Americas, particularly in French Guiana and Suriname. 3

Between French Guiana and Suriname, we can find communities from the Noir Marron population, like Ndjuka, Saramaka, Aluku and Paramaka. Those communities are still living today in the Amazonian forest in relatively isolation from European and indigenous groups for around four centuries. Interestingly, they still preserve a strong African background in their Creole languages and traditions. One interesting anthropological question is to better understand their remarkable African heritage by using genetic markers. 4

First we need to better understand the complex genetic diversity inside of the African continent. In our study recently published in Science , we characterized the genetic variation of Bantu-populations from West Africa and their important migrations across sub-Saharan Africa. More specifically, we described the routes of the Bantu expansion from West Africa to East and South African regions, and the changes in admixture patterns across those regions. This valuable information allows us to explore other migration routes of African populations to North America, as you can see in the recent study of Patin et al., and to South America, as we are going to see in this presentation. 5

In South America, we analysed over 100 people from the four Noir Marron communities and African-descendant populations from Brazil and Colombia. We compare their genetic diversity with their putative ancestors in West Africa. To do that, we also analysed over 100 people from West African regions in Benin, Ivory Coast and Mali. For each participant, we generated a new genomic dataset for over 4.3 million Single Nucleotide Polymorphisms (SNPs). 6

Briefly, I’m going to explain the main approach in genome -wide analyses to infer the ancestral origin of people. First, we compare our new dataset with available genomic data from continental populations in Africa, Europe, Asia, and America. For example, we characterized the genomic diversity of each chromosomal segment of people from the same continent, with one category like one particular colour. We can differentiate the continental ancestry of each individual, based on their genomic affinities with people from each continent. We then estimated the continental genomic ancestry of people from South America based on this approach. 7

We used two different methods based on local and global ancestry inferences. In both methods, we obtained similar results. As we can see, in the local ancestry inference, most of the genome in the Noir Marron population is in red, which means this population has a high African ancestry. In contrast, other African-descendant populations in South America present different patterns of admixture, especially with European groups like in the African-Brazilian, or with European and Native American groups like in the African-Colombian. Here you can see the average estimate in each population based on the global ancestry inference, including other African-descendants in the Americas. As before, the Noir Marron has the highest African ancestry that is around 98%, whereas the other African-descendant populations present complex patterns of admixture. 8

Furthermore, we found the same strong African genetic ancestry in each Noir Marron community, reflecting their low gene-flow with other non-African groups. Therefore, we are interested to infer the geographical origin of this strong African legacy. 9

We extended our study to more African populations, representative of different geographical regions. In this method, we can characterize the geographical distribution of genetic patterns inside of the continent. As you can see, West African populations have a similar genetic pattern, which is present in high proportions in African-descendant populations. Interestingly, the genetic profile of the Noir Marron strongly matches with the genetic profile of populations residing in historical African coastal regions present during the slave trade, such as Gold Coast in modern Ghana and the Bight of Benin in modern Benin and Western Nigeria. 10

We confirmed those results in multidimensional space based on Principal Component Analysis (PCA). As you can see, Noir Marron individuals, in black dots, closely overlap with African populations from Ghana, Benin, and Western Nigeria. Therefore, this study provides a better understanding of the African genetic links of the Noir Marron population. 11

In summary, the new genome-wide data provide a better understanding on the genetic diversity of African-descendant populations from South America and the impact of the slave trade. We detected a strong African genetic legacy (~98%) in the Noir Marron population, which have been maintained after centuries of forced separation. The new findings establish a deeper insight into the putative founder group of the Noir Marron population, which has been linked with the historical African coastal regions of Gold Coast (modern Ghana) and Bight of Benin (modern Benin and West Nigeria). 12

I would like to thanks to hundreds of participants in this study, to my partners Jean-Michel Dugoujon and Cesar Fortes-Lima, and thank you for your attention. I’ll be happy to answer any question that you might have. You could find further information about this study in our next publication at the American Journal of Human Genetics. 13