While gene flow between distantly related populations is increasingly recognized as a potentially important source of adaptive genetic variation for humans, fully characterized examples are rare. In addition, the role that natural selection for resistance to vivax malaria may have played in the extreme distribution of the protective Duffy-null allele, which is nearly completely fixed in mainland sub-Saharan Africa and absent elsewhere, is controversial. We address both these issues by investigating the evolution of the Duffy-null allele in the Malagasy, a recently admixed population with major ancestry components from both East Asia and mainland sub-Saharan Africa. We used genome-wide genetic data and extensive computer simulations to show that the high frequency of the Duffy-null allele in Madagascar can only be explained in the absence of positive natural selection under extreme demographic scenarios involving high genetic drift. However, the observed genomic single nucleotide polymorphism diversity in the Malagasy is incompatible with such extreme demographic scenarios, indicating that positive selection for the Duffy-null allele best explains the high frequency of the allele in Madagascar. We estimate the selection coefficient to be 0.066. Because vivax malaria is endemic to Madagascar, this result supports the hypothesis that malaria resistance drove fixation of the Duffy-null allele in mainland sub-Saharan Africa.

The genetic basis of androstenone anosmia has been well-studied due to androstenone's putative role as a human sex pheromone and its presence in pork meat. Polymorphisms 2 have been identified on the olfactory receptor gene OR7D4, which significantly affect perception of androstenone pleasantness and intensity in several western populations.This study aims to investigate androstenone sensitivity and the influence of OR7D4 polymorphisms in non-western populations. Androstenone perception was tested in 132 individuals from Madagascar using a double 3-Alternative Choice test with two concentrations of androstenone (0.17 µg/ml and 1.7 µg/ml).We found that Malagasy populations described this molecule in a similar way to European populations, and 21% of the sample was not able to smell androstenone. In contrast to previous studies, there was no significant evidence of the influence of rs61729907: C>T (R88W) and rs5020278: C>T polymorphisms (T133M) on androstenone sensitivity in Malagasy populations. We found, however, a significant effect of the polymorphism rs61732668 (P79L), and a significant difference in androstenone perception between populations in different locations across Madagascar.This study indicates the existence of population specific factors to androstenone sensitivity, suggesting that population history has a role in shaping an individual's smell and flavor preferences, and food preferences in general.3

Madagascar is an exceptional example of island biogeography. Though a large island, Madagascar's landmass is small relative to other places in the world with comparable levels of biodiversity, endemicity, and topographic and climatic variation. Moreover, the timing of Madagascar's human colonization and the social-ecological trajectories that followed human arrival make the island a unique case study for understanding the dynamic relationship between humans, environment, and climate. These changes are most famously illustrated by the mass extinction of the island's megafauna but also include a range of other developments. Given the chronological confluence of human arrival and dramatic transformations of island ecologies, one of the most important overarching questions for research on Madagascar is how best to understand the interconnections between human communities, the environment, and climate. In this review paper, we contribute to the well-established discussion of this complex question by highlighting the potential for new multidisciplinary research collaborations in the southwest part of the island. Specifically, we promote the comparison of paleoclimate indicators from securely dated archaeological and paleontological contexts with Western Indian Ocean climate records, as a productive way to improve the overall resolution of paleoclimate and paleoenvironmental reconstruction for the island. Given new archaeological findings that more than double the length of Madagascar's human occupation, models of environmental transformation post-human arrival must be reassessed and allow for the possibility of slower and more varied rates of change. Improving the spatial and temporal resolution of paleoclimate reconstruction is critical in distinguishing anthropogenic and climate drivers of environmental change. It will also increase our capacity to leverage archaeological and paleoclimate research toward resolving modern challenges, such as environmental conservation and poverty alleviation.