A Genomic Investigation of the Malagasy Confirms the Highland–Coastal Divide, and the Lack of Middle Eastern Gene Flow

Abstract

The island of Madagascar is among the last of the major landmasses to have been populated by humans, yet this colonization remains one of the least well understood. Madagascar is the world’s fourth largest island by area, and is separated from mainland Africa by the Mozambique Channel. This separation occurred during the early Cretaceous, and Madagascar has been entirely isolated from the mainland since at least the early Miocene (McCall 1997). The long history of isolation led to a largely endemic flora and fauna that contains many ancient and unique lineages such as the lemurs, and makes Madagascar one of the world’s most important biodiversity hotspots (Ganzhorn et al. 2001). In contrast, humans arrived in Madagascar only within the last few thousand years, the result of the confluence of two of humanity’s great population expansions—the Bantu-speaking and Austronesian (Dewar and Richard 2012; Dewar and Wright 1993). Subsequent human activity has had devastating effects on Madagascar’s biodiversity, with the extinction of almost all of the megafauna (Burney et al. 2004) and the loss of most of the forest that once existed, including a >50 percent reduction over the last 70 years (Green and Sussman, 1990). Understanding the peopling of Madagascar helps shed light on both human movements around the Indian Ocean, and the role that humans have played in Madagascar. Nonetheless, much of the detail regarding the origins of the Malagasy and their settlement of Madagascar remains unknown. In this chapter, I use genomic data to address two important albeit very basic questions about the Malagasy. First, how do groups from the Malagasy littorals differ genetically from those that live in the highlands; and second, from how many source populations do the Malagasy descend?

I would like to thank Gwyn Campbell and the Indian Ocean World Centre for arranging the conference from which this chapter originated, and for inviting me to participate.