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Traditional pastoralists survive in few places in the world. They can still be encountered in the African Sahel, where annual alternations of dry and wet seasons force them to continual mobility. Little is known about the genetic structure of these populations. We present here the population distribution of 312 hypervariable segment I mitochondrial DNA (mtDNA) and 364 Y-short tandem repeat haplotypes in both farmer and pastoralist groups from the Lake Chad Basin and the West African Sahel. We show that the majority of pastoral populations (represented in the African Sahel by the Fulani nomads) fail to show significant departure from neutrality for mtDNA as evidenced by Fu's Fs statistics and exhibit lower levels of intrapopulation diversity measures for mtDNA when contrasted with farmers. These differences were not observed for the Y chromosome. Furthermore, analyses of molecular variance and population distributions of the mtDNA haplotypes show more heterogeneity in the sedentary groups than in the pastoralists. On the other hand, pastoralists retain a signature of a wide phylogenetic distance contributing to their male gene pool, whereas in at least some of the farmer populations, a founder effect and/or drift might have led to the presence of a single major lineage. Interestingly, these observations are in contrast with those recorded in Central Asia, where similar comparisons of farmer and pastoral groups have recently been carried out. We can conclude that in Africa, there have been no substantial mating exchanges between the Fulani pastoralists coming to the Lake Chad Basin from the West African Sahel and their farmer neighbors. At the same time, we suggest that the emergence of pastoralism might be an earlier and/or a demographically more important event than the introduction of sedentary agriculture, at least in this part of Africa. The project was supported by the Grant Agency of the Czech Republic (Grant no. 206/08/1587), the Portuguese Fundação para a Ciência e a Tecnologia (project—PTDC/ANT/66275/2006; post-doc grant—SFRH/BPD/64233/2009), and the Italian Ministry of University (MIUR-PRIN2007). Instituto de Patologia e Imunologia Molecular da Universidade do Porto is an Associate Laboratory of the Portuguese Ministry of Science, Technology and Higher Education and is partially supported by FCT, the Portuguese Foundation for Science and Technology.

In the African Sahel the history of which is marked by recurring food crises, agriculture and food gathering have remained until recent years complementary activities. In the Soninke country, in particular, food gathering is a regular, socially organized practice, which provides complementary food in periods of plenty and food substitutes during times of crisis. When there is no famine it plays an important part in nutritional balance. This formerly servile work has progressively concerned all social groups since the end of the 19th century, being in that way part of a more global evolution of Soninke society. At present, however, there is a decrease in food gathering, which varies according to the region and is related to the degradation of the vegetation cover and changes in the way of life. In the high Senegal valley it is due, in particular, to the monetization of the economy with the increase in migration of the labour force, and the transformation of the production system with the creation of irrigated perimeters. This trend may well have been strengthened by the lack of interest given to this activity in the fields of research and development. Food gathering practices depend on the knowledge of the vegetation and on different harvesting and preparation techniques. Food gathering plays as much a part in the management of the environment as agriculture or breeding stock, fishing or hunting. These practices are also strongly imbued with social and symbolic meaning, as the oral statements and the food gathering songs show. As a means of subsistence and a sign of poverty during times of famine, it can be either considered praiseworthy or as something to be denied. When a crisis occurs not only is survival in jeopardy but also social identity. This ambiguous perception of food gathering is the backcloth to its present depreciation and its decline. Without losing sight of the ambivalence of this practice in the Soninke society - and in other African societies - the consequences of its decrease from the point of view of knowledge and preservation of the environment can be questioned. The decline of food gathering also reinforces the present trend for uniform agricultural systems and increases their vulnerability to different forms of ecological and economic risks. Before the disappearance of these skills with their related practices should not these same skills be taken into consideration and reassessed, and if so, how?, En Afrique sahélienne, marquée dans son histoire par des crises alimentaires récurrentes, l'agriculture et la cueillette ont été des activités complémentaires jusqu'à ces dernières années. En pays soninké, en particulier, la cueillette est une pratique régulière et socialement organisée, qui procure des aliments de complément en période d'abondance et des nourritures de substitution en période de crise. En l'absence de famine, elle joue un rôle important dans l'équilibre nutritionnel. Cet ancien travail servile a progressivement concerné tous les groupes sociaux depuis la fin du XIXème siècle, participant ainsi d'une évolution plus générale de la société soninkée. Actuellement, cependant, on constate un recul de la cueillette, plus ou moins marqué selon les régions, recul qui est lié à la dégradation du couvert végétal et au changement des modes de vie. Cela est dû notamment dans la haute vallée du Sénégal, à la monétarisation de l'économie, avec l'essor des migrations de travail, et à la transformation du système de production, avec la création de périmètres irrigués. Cette tendance a sans doute été renforcée par le manque d'intérêt pour la cueillette dans les milieux de la recherche et du développement. Cette activité repose sur la connaissance de la végétation et sur différentes techniques de récolte et de préparation. Elle joue un rôle dans la gestion de l'environnement, au même titre que l'agriculture, l'élevage, la pêche ou la chasse. Cette pratique a aussi une dimension sociale et symbolique, comme le montrent les témoignages et les chants de cueillette. En tant que moyen de subsistance et signe de pauvreté, la cueillette peut être à la fois un objet d'éloge et de dénégation. En temps de crise, en effet, non seulement la survie est menacée mais aussi l'identité sociale. Cette perception ambigüe de la cueillette constitue l'arrière plan de sa dévalorisation et de son déclin actuels. Sans perdre de vue l'ambivalence de la cueillette en milieu soninké - comme ailleurs en Afrique -, on peut s'interroger sur les conséquences de son recul au niveau de la connaissance et de la protection de l'environnement. Le déclin de la cueillette va dans le sens de l'uniformisation des systèmes agricoles, tout en augmentant leur vulnérabilité aux risques écologiques et économiques. Avant que ne disparaissent ces savoir-faire et les différentes pratiques qui leur sont liées, ne faudrait-il pas les prendre en considération et les réévaluer ? Si oui, selon quelles modalités ?