"We find that families who are at the forefront of a range expansion into new territories had greater reproductive success. In other words, that they had more children, and more children who also had children," Labuda explained. "As a result, these families made a higher genetic contribution to the contemporary population than those who remained behind in what we call the range core, as opposed to the wave front.Science DOI: 10.1126/science.1212880
The research confirms in humans a phenomenon that has already been observed in other species with much shorter generation spans. "We knew that the migration of species into new areas promoted the spread of rare mutations through a phenomenon known as 'gene surfing', but now we find that selection at the wave front could make this surfing much more efficient," Excoffier said. This evolutionary mechanism in combination with founder effects and social or cultural transmission of reproductive behavior could explain why some genetic diseases are found at an elevated frequency in the Charlevoix and Saguenay Lac Saint-Jean regions where the study was carried out, as rare mutations can also surf during a range expansion.
Deep Human Genealogies Reveal a Selective Advantage to Be on an Expanding Wave Front
Claudia Moreau et al.
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 1 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.