The influence of clan structure on the genetic variation in a single Ghanaian village
"Our result of clan specific Y-chromosomal lineages together with results of de Filippo et al indicate a scenario where several patrilineally related genetic lineages constitute a ‘tribe’. The fact that we find similar patrilineal lineages across West Africa raises the intriguing possibility that many ethnic groups (or ‘tribes’) or even ethnolinguistic groups that identify themselves as homogenously related entities, consist of the same small number of closely related genetic lineages."
The genetic structure of human populations is strongly shaped by the social, cultural and demographic processes that govern migration and settlement of individuals. Such processes are presumed to act on a number of different geographical scales, varying from a local scale – for example, within a single village, a more regional scale – over distances of a few 100 km – to sub-continental scale, reflecting distances of many hundreds to thousands of kilometres. Exactly how these processes operate on a local scale, and how these local effects influence the genetic patterns that we see on regional or sub-continental scale has not been tested extensively. Nevertheless, genetic variation over large geographic scales has been routinely investigated to infer the relationships among populations in historical contexts.
The frequently observed clinal pattern of reduced genetic diversity away from Africa is seen as strong evidence for the out-of-Africa movement(s) of anatomically modern humans.3 On a sub-continental scale, the demographic changes that are inferred from genetic data are still hotly debated for Oceania,4 Europe5 and the Americas.6 Within Africa south of the Sahara, such studies are now also emerging slowly,7, 8, 9 mainly because the distribution and size of samples are limited. Most population genetic research in Africa has focused on the complex expansion patterns of Bantu-speaking people from central Africa to the south, which seems to have left strong signals in uniparental and autosomal markers across the genome.
For West Africa, however, there are some detailed genetic studies on smaller scales. For instance, Coelho et al reveal strong patterns in the genetic structure of human populations on the small island of Sao Tomé that were influenced by spatial- and temporal-specific events.
Ottoni et al show strong founder effects and drift that have resulted in very different paternal lineages in two Libyan villages. Barbieri et al found a clear structure in the paternal line that matches linguistic affiliation across ethnolinguistic groups in Burkina Faso.
In contrast, Veeramah et al show that there is little genetic structure among neighbouring ethnic groups in southern Nigeria despite the strong language differentiation among them. Apparently, this region has a particularly high diversity of ethnicities, languages, and subsistence modes, and a complex correspondence with uniparental genetic variation.
For long, anthropologists have recognized problems with too simplistic interpretations of patterns of genetic variation at a macro-scale and called for more local studies.16, 17 We consider three reasons to investigate social–cultural factors in relation to genetic studies on local, regional or sub-continental scale in West Africa.
First, based on oral tradition, many Africans claim major migration events in their ancestry. Genes have been on the move within Africa on a large scale for probably a long time, for highly variable reasons. Therefore, to better understand African migration history from a genetic point of view, we need a much denser geographical sampling. Second, the role of social factors in asymmetric gene flow between sexes has been recognized before.
On a continental and sub-continental scale, this can be explained by sex-biased rates of admixture, subsistence mode and marital residence patterns; a general consensus is the higher female to male migration rate in Africa south of the Sahara. Third, population labels (ethnicity, language and geographic ‘origin’) are often used and understood to be rigid entities, but it is widely recognized that in many cases these group labels are very flexible and influenced by social factors and distance.
We take a next step towards a detailed, local scale genetic study and describe the results of a genetic survey among 205 males from a single Bimoba village in the Garu-Tempane district in Upper East Region of Ghana, Africa. In this area, Leiden University Medical Center was involved in medical genetic research projects since 2004. We investigate the population genetic structure in this region to better inform a number of genetic association studies.
There is very little known about the origins of the Bimoba. Most sources state that the Bimoba, as a tribe, represent a combination of a variable number of smaller groups. They are closely related to the Moba from neighbouring areas in Togo. The Bimoba speak Moba, which is part of the Gur language group (Niger-Congo family).
In contrast to surrounding tribes, the Bimoba currently belong to the acephalous tribes, that is, there are no kings, chiefs or big men.
Among the Bimoba, clan and clan group are the social focal points. These clans are patrilineally organized. All males in the village studied belong to six different self-identified clans: Baakpang, Tont, Miir, Sisiak, Najakbab and Nabakib. Although history varies from clan to clan, they all share the history of their first chief, Turiŋme.
When the Bimoba settled in north-eastern Ghana and western Togo, they occupied the least fertile and most remote parts of this region, mainly in the area they still live in. This suggests that they were not able to, or did not want to rival the existing political forces at large. As a result, the Bimoba still are a group with limited power in this region. As most populations in the Sahel region, the Bimoba are pastoral agriculturalists. Both animal husbandry and crop fields are important for subsistence. The Bimoba are polygynous and practice clan exogamy, that is, within-clan marriage is prohibited. Marriage divorce is possible, but not common. Meij et al provides a more detailed anthropological description of the Bimoba of north-eastern Ghana.
The males in our sample were genetically screened for a set of 15 autosomal short-tandem repeats (STRs), 15 Y-chromosomal STRs and for 65 biallelic Y-chromosomal single-nucleotide polymorphisms (SNPs) defining Y-haplogroup E and sub-lineages thereof. In addition, a 365-bp sequence in HVS1 of their mitochondrial DNA (mtDNA) was sequenced.
Research area and population background
The study area is located in the upper east region of Ghana, between 0.226W–10.689N and 0.81W–10.837N. Within this study area of approximately 360 km2, there are about 23 000 inhabitants living in over 1200 individual compounds, which are clustered in 24 villages. The upper east region of Ghana is an area with little development towards a modern industrialized society. Most of the inhabitants are traditional agriculturalists. People live in family compounds, which are essentially small farms that produce at subsistence level.
The population has a patrilocal and patrilineal structure: the women are accepted to their husbands’ clan and the males stay in or around their fathers’ compound. It is custom not to marry inside one’s clan (clan-exogamy) and polygyny is widespread.
As there are no civil registries in the region, GPS coordinates of all villages and compounds within the study area were registered and assigned a unique identification number.
The name, sex, age and tribe of each individual were collected from interviews during field visits to each household. We interviewed the head of the household (landlord) about the ethnic group and the clan of each individual. In addition, we interviewed the elders of the village from different clans on their male ancestors.
The interviews were taken by a staff member from The Netherlands together with a translator enroled in the project. The translator was a lifelong inhabitant of the village under study. The demographic information from these interviews is continuously checked during the annual follow-up by revisiting all households, thereby also registering individuals that were newly born, deceased, or migrated. We also performed random, independent double household visits and this has shown that the database is accurate and reliable.
Sampling procedure and ethical approval:
For the purpose of this study, we concentrated on a single Bimoba village. Genetic data were obtained from 205 men living in 93 compounds (Figure 1). The inclusion criterion was to sample at least one male from each compound in the village, two males were preferred where available, and closely related individuals such as father–son pairs were randomly included. In this village, members of the following six different Bimoba clans were sampled: Baakpang (n=90), Tont (n=43), Miir (n=55), Sisiak (n=3), Najakpab (n=8) and Nabakib (n=6). Baakpang and Tont clans claim common ancestry, similarly to Miir and Sisiak. Biological material was collected using buccal swabs. DNA was isolated from buccal swab samples using the QIAamp DNA Mini Kit (Qiagen, Hilden, Germany), according to the manufacturers’ standard protocol. This research project was executed with the informed consent of participating individuals, and approved by the ethical committees of the Ghana Health Service and the Leiden University Medical Center.Please read the full piece via: http://www.nature.com/ejhg/journal/v21/n10/full/ejhg201312a.html
Paulina says: I'm going to be brutally honest, most of what I read in this Journal has gone way-over-my-head, I'm just not clever enough to understand......, but I'm beyond ecstatic to be learning about the Bimoba Clan of the Upper East Region of Ghana.....a tribe I knew nothing about until today...... For all those interested in genetic lineages -do read the full Journal via: http://www.nature.com/ejhg/journal/v21/n10/full/ejhg201312a.html
For more info about the Bimoba Clan visit: http://www.bimoba.com/html/bimoba.htm