Post-admixture selection favours Duffy negativity in the Lower Okavango Basin

Human Population Genetics and Genomics 2026;6(2):0008 | https://doi.org/10.47248/hpgg2606020008

Original Research Open Access

Post-admixture selection favours Duffy negativity in the Lower Okavango Basin

Artem Kasianov ^1,2 , Anne-Maria Fehn ^1,2 , Maitseo Bolaane ³ , Gaseitsiwe Masunga ⁴ , Ezequiel Chimbioputo Fabiano ^1,2,5 , Jorge Rocha ^1,2,6

1. CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal
2. Biopolis Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, 4485-661 Vairão, Portugal
3. San Research Centre, University of Botswana, P.O. Box 70375, Gaborone, Botswana
4. Okavango Research Institute, University of Botswana, Private Bag 285, Maun, Botswana
5. Department of Wildlife Management and Tourism Studies, University of Namibia, Katima Mulilo Campus, Private Bag 13301, Katima Mulilo, Namibia
6. Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, 4099-002 Porto, Portugal

Correspondence: Artem Kasianov

Academic Editor(s): Carina Schlebusch

Received: Mar 29, 2026 | Accepted: Jun 5, 2026 | Published: Jun 29, 2026

Cite this article: Kasianov A, Fehn A, Bolaane M, Masunga G, Fabiano EC, Rocha J. Post-admixture selection favours Duffy negativity in the Lower Okavango Basin. Hum Popul Genet Genom. 2026;6(2):0008. https://doi.org/10.47248/hpgg2606020008

Abstract

The FY*BES allele in the human Duffy blood group is nearly fixed across much of sub-Saharan Africa. Individuals homozygous for this allele (Duffy-negative) were considered resistant to red blood cell invasion by the malaria parasite Plasmodium vivax, restricting its distribution across the continent. However, recent studies have demonstrated that P. vivax can infect Duffy-negative individuals and is widespread among African populations where FY*BES predominates. As these findings may challenge the long-standing assumption that P. vivax protection is the driving force elevating FY*BES frequencies, the evolutionary relationship between Duffy negativity and parasite resistance should be re-evaluated across diverse geographic, ecological and epidemiological settings. Previous research investigating the role of natural selection in increasing the frequency of the FY*BES allele has primarily centered on admixed populations with African and non-African ancestries from regions with long-documented P. vivax transmission. Here, we focus on the Khwe foragers from the lower Okavango River Basin of northern Namibia and Botswana, where the parasite has only recently been reported. Using locus-specific statistics, simulations of neutral scenarios, and local ancestry inference, we found evidence for strong post-admixture selection promoting FY*BES introgression from Bantu-speaking populations into the Khwe. If P. vivax resistance indeed drove the rise in FY*BES allele frequency, our findings suggest that the parasite has been present in the region at least 500 to 1,000 years ago.

Keywords

Duffy negativity, Plasmodium vivax, malaria resistance, post-admixture selection, Okavango River Basin

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