Gene surfing is a process in population expansion whereby certain variations become prominent and dominant in a short time, appearing to skip the slow, steady, uniform accumulation of variegation and diversification. According to a study of the population structure and genealogies of Saguenay Lac-Saint-Jean in Quebec, this type of drastic change accompanied the immigrant wave front that spread over the area in the 17th century. "Deep Human Genealogies Reveal a Selective Advantage to Be on an Expanding Wave Front" in Science magazine describes the resulting demographics.
Since their origin, human populations have colonized the whole planet, but the demographic processes governing range expansions are mostly unknown. We analyzed the genealogy of more than one million individuals resulting from a range expansion in Quebec between 1686 and 1960 and reconstructed the spatial dynamics of the expansion. We find that a majority of the present Saguenay Lac-Saint-Jean population can be traced back to ancestors having lived directly on or close to the wave front. Ancestors located on the front contributed significantly more to the current gene pool than those from the range core, likely due to a 20% larger effective fertility of women on the wave front. This fitness component is heritable on the wave front and not in the core, implying that this life-history trait evolves during range expansions.
So gene surfing in an expanding colonization phase can produce a genetic revolution whose effects will be felt for hundreds or thousands of years downstream in history.
We wonder if the same wave front demographics might explain some of the following population phenomena:
- Large scale triumph of Norman male lineages following the conquest of England in 1066.
- Selective expansion of Middle Eastern genes in Tennessee (including Cherokee families, Jewish male and female lines and Melungeons)
- Relatedness among Jews and "Jewish diseases"
- Diversity-within-uniformity of Polynesians
- Population replacement of Old European (U, N) by Middle Eastern genes (T, J) in Europe as a result of the Neolithic Agricultural Revolution
Many students of history are puzzled why old populations have the allele frequencies and heterozygosity clines they have. Genetic drift is only part of the answer. Gene surfing and selection in deep history are the rest of it.
More information about Melungeons
Toward a Genetic Profile of Melungeons in Southern Appalachia