EAGER: Investigating the Evolutionary and Environmental Bases of Twinning in Human Populations

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In this EAGER project, the investigators will study the occurrence of twins in human populations, with a focus on high twinning rates. Fraternal twinning rates vary across populations, and this variation and the potential adaptive advantages of having twins are not fully understood. Previous research by these investigators and others suggest that both genetic and environmental factors are involved. This project will collect initial information on the scale and timing of twinning in one population with an extremely high twinning rate, which will provide a foundation for subsequent research projects to understand the cultural, biological, evolutionary, and environmental contexts of multiple births in modern humans. The project also supports international research collaborations and may lead to findings that inform fertility research. Spontaneous dizygotic (DZ) twinning occurs with the release and fertilization of two oocytes. A genetic component to dizygotic twinning has long been recognized, potentially including genes related to follicle cohort size and multiple implantation, but no clear inheritance pattern has been identified. Environmental factors such as smoking may also influence twinning rates. The investigators will collect information on twin occurrence in a village in southern India, to reconstruct when the village started to have twin frequencies that are out of the normal range of other Indian populations, and to begin to explore the potential effects of microevolutionary processes and environmental chemical exposure.