In the 1830s in the*deep forests of Quebec, Canada, a restless population of pioneers began a lengthy, risky experiment. Quebec City, built by the French by the St. Lawrence River, was growing fast. To the north, along the Saguenay River, stretched a vast, nearly untouched forest. This rich but brutal country soon attracted loggers and young farming families with a taste for work, risk, and opportunity. Up the valley they went, building one small village after another, creating a wave of settlement moving up the Saguenay. From a biologist’s point of view, such a migratory wave can concentrate not just particular types of people on its frothy front edge; it can also concentrate and aid the expansion of any genes that may encourage those people to migrate...
But a migratory wave can also allow genes friendly to migration to drive their own selection. A notable, if noxious, example is the South American cane toad. Introduced to northeastern Australia in the 1930s, it now numbers more than 200 million and is advancing across the continent at 30 miles a year. The leading toads hop on legs that are 10 percent longer than those of their 1930s ancestors—and measurably longer than the legs of toads even a mile behind them. How so? Toads that are both restless and long legged move to the front, bringing any restless, long-legged genes with them. There they meet and mate with other restless, long-legged toads to create restless, leggy offspring that move to the front and repeat the cycle.
Laurent Excoffier, a population geneticist at the University of Bern, thinks something similar occurred with the Quebec loggers. In a 2011 paper Excoffier and some colleagues analyzed centuries of Quebec parish birth, marriage, settlement, and death records and found that the pioneer families behaved and bred in a way that spread both their genes and the traits that drove them to the front. These wave-front couples married and mated sooner than did couples back home, perhaps because they were more impatient folks to begin with and because the frontier gave them access to land and a social atmosphere favorable to starting sooner. This alone produced more children than the “core” families who stayed behind did (9.1 per family versus 7.9, or 15 percent more). And because these children in turn proved likelier to marry early and have more children, each pioneer couple left behind 20 percent more offspring altogether. Twenty percent more offspring produces a huge evolutionary advantage. In this case it rapidly raised the share of these families’ genes and cultures within their own population—and thus within North America’s larger population.
Excoffier believes that if this “gene surfing,” as some call it, happened often as humans scattered around the globe, it would have selected for multiple genes that favor curiosity, restlessness, innovation, and risk taking. This could, he says, “help explain some of our exploratory behavior.” Exploration may thus create a self-reinforcing loop, amplifying and spreading the genes and traits that drive it.