Dispersal, effective population size, and the genetic structure of the contemporary United States

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Abstract
I estimate effective population size (Ne) and the inbreeding coefficient (FST) for contemporary United States using Wright's isolation by distance model (Wright: Genetics 28:114–138, 1943) and parent‐offspring dispersal distances obtained from individuals surveyed as part of a study of modern dispersal patterns. Ne is estimated to be minimally 3.61 × 107 and more likely closer to 8.05 × 107; based on these values, FST is between 1.59 × 10−7 and 9.28 × 10−9, depending on whether it is measured relative to the United States population or the world at large. Not all the assumptions of the isolation by distance model are met by modern populations, and thus the results must be interpreted with caution. They suggest, however, that both mobility within and immigration into contemporary United States are great enough to make the probability of inbreeding and random genetic drift negligible factors in producing future evolutionary change. In contrast, gene flow, acting as both a constraint against geographic differentiation within the United States and by introducing new genes via international immigration, is likely to be a dominant evolutionary force in this population.