The Rhythm of the Tide

Standing deep inside the archives of the Roman Catholic Church’s Canadian headquarters, it suddenly struck me that this was an odd place to find evidence that people are still evolving.

That human evolution has continued into modern times was, until recently, a mostly theoretical idea debated among experts because there simply was no data. But as an evolutionary biologist, I had my own perspective. My research has mostly been on ants, which are common and diverse, making them ideal subjects for understanding evolutionary processes. In some ways ants and humans have a lot in common. Leafcutter ants create enormous underground nests that house millions of individuals, each with specialized tasks—not unlike our cities. They grow their own food in the form of a fungus that they domesticated from wild ancestors, much like human farmers. Ants even use antibiotics to treat diseases. I knew that these characteristics had not buffered them from natural selection, so why should we humans be any different?

Then in 2011, I read a study suggesting that small evolutionary changes had taken place among people living as recently as the 19th and 20th centuries.¹ I decided that I had to go see the evidence for myself, so I arranged to visit the tiny Quebec island of Ile aux Coudres in the St. Lawrence River. Here was a chance to glimpse firsthand how our very recent evolutionary past meets our present.

The study leader, Emmanuel Milot, met me in the arrival area of Montreal’s Pierre-Elliott-Trudeau airport wearing a black T-shirt with a white Jesus fish emblazoned with the word “DARWIN,” leaving little doubt that he was a fellow evolutionary biologist. After a short driving tour of downtown Montreal, we ducked into a microbrewery in the historical district to escape a sudden downpour that made the cobblestone streets glow yellow with light reflected from the streetlamps.

Milot told me how he had started out working as a field research assistant surveying birds in remote parts of Quebec, before pursuing doctoral work on the wandering albatross in the Kerguelen Islands, a rugged French outpost in the southern Indian Ocean near Antarctica. The wandering albatross is an iconic species for bird enthusiasts, and Milot described his project as a sort of ornithological holy grail. He spent months at a time on French research vessels traveling to distant parts of the archipelago taking blood samples and other measurements. He once caught an albatross with a band around its leg indicating that it had been alive and breeding before Milot was even born.

Working with such a long-lived species got him thinking about issues that don’t affect animals with shorter lives, like how long it takes for a young bird to reach maturity and begin to reproduce, and how the body begins to break down with old age. It wasn’t long before Milot would make the connection between his birds and another long-lived species—humans.

In this he was helped by his colleague and former supervisor Francine Mayer, whom we visited the next morning. In the flower-filled garden behind her house, Mayer explained how, as a graduate student, she became interested in the demographic and genetic structure of human populations and how they change through time. In the 1960s, she was part of a research group that started to search for isolated communities where records were available on a fairly small population over multiple generations.

As an island, Ile aux Coudres was ideal. Although it is only a mile and a half from the north shore of the Saint Lawrence, dangerous currents and icy conditions during part of the year kept its inhabitants from being as closely connected to nearby villages as were other communities. What’s more, another researcher, Pierre Philippe, had visited the island in 1967 and obtained permission from the community and from the local priest to transcribe parish birth, death, and marriage records for demographic research. Together with her graduate student Mireille Boisvert, Mayer worked for three years to construct a genealogy describing the marriages of 572 women and their 4,002 children, spanning from 1800 through the 1960s.

Milot joined the research team as a postdoc in 2009 and discovered a surprising trend in the birth data. Over just a few generations, the average age at which a woman became a mother dropped from 26 to 22. It seemed that those women on Ile aux Coudres who started having children at younger ages also had larger families. Intriguingly, their daughters tended to do the same.

Milot knew from his studies of birds that the timing of reproduction is a trait that often responds to natural selection. A handful of other studies on historical human populations hinted that natural selection might also affect birth timing in humans, but no definitive test had proven it.² To do so, he would need to show that there was a genetic basis for the decrease in age at first reproduction and that factors other than natural selection (like improving nutrition and healthcare) did not fully explain the changes. Using a mathematical model borrowed from the study of animal breeding, he was able to tease apart these factors.

The model predicted how similar any two individuals should be based on how closely related they are, taking into account their similar environment. This allowed Milot to calculate the “predicted breeding value” of age at first reproduction, which is an estimate of the extent to which the value of that trait is explained by a person’s genes, and how it compares to the population average. If, for example, a particular woman had her first child at age 23, and the average age at first reproduction in the population were 25, her breeding value would estimate how much of that two-year difference was inherited from her parents. Over eight generations, the average predicted breeding value dropped significantly, suggesting an evolutionary response.

Milot and his colleagues also found no evidence that the population’s health was changing in a meaningful way over this period, by using infant and juvenile survival rates as a proxy for overall health. The team also excluded the possibility that random genetic fluctuations could account for changes in age at first reproduction by determining that the more closely related any two women were, the more likely they were to have given birth to their first child around the same age.

The best remaining explanation for the observed decrease in the age at first reproduction was evolution by natural selection. Darwin had his Galapagos finches; Milot had his Quebecois islanders.

The next day Milot and I began our 
journey towards Ile aux Coudres. As we approached Quebec City, we passed the
spot where the British secretly climbed
a cliff and surprised the French army,
beginning the 1759 battle that would end
France’s control of Quebec. The Quebecois
were descendants of French settlers who,
beginning in 1608, founded a series of settlements along the Saint Lawrence known
as Nouvelle France. French immigration
effectively ended following their defeat by
the British, and French Canadians became
isolated not only from their French ancestors but also from their neighbors, due to linguistic and religious differences.

The pattern of settlement and migration by the French Canadians was, in a way, a microcosm of the history of the human species. The first Homo sapiens began migrating out of northeast Africa around 50,000 years ago, establishing small populations in the Middle East. As the population grew, waves of settlers expanded west into Europe and east into Asia. Some particularly adventurous pioneers made their way across stretches of open ocean to colonize the islands of Indonesia and the South Pacific, as well as Australia, while a different wave of nomads crossed the Bering Strait and became the first people to settle the Americas.

Here was information that Milot and I could never hope to obtain for any other species than humans.

French Canadian migration followed a similar pattern: As the population of Quebec City grew, a few pioneers would set up farms on the frontier, and their descendants would grow in numbers and then migrate to new territories, repeating the cycle. The first settlers to reach Ile aux Coudres were 30 families that arrived between 1720 and 1773. At the time, the island was at the edge of settled territory in Nouvelle France. All land on the island was divided up among the families in long, thin strips that allowed access to the sea as well as space for planting crops. The population more than doubled between 1765 and 1790, and families were forced to divide their strips of land among their children. By the beginning of the 20th century the population exceeded 1,000, reaching 1,585 inhabitants by 1950.

Women on Ile aux Coudres averaged between six and 10 surviving children. In their research article, Milot and his colleagues emphasized that the island inhabitants experienced “natural fertility,” meaning that no effective forms of birth control or family planning were available. Industrialization tends to reduce both birth rates and death rates, a phenomenon known as the “demographic transition.” Remarkably, as of the 1960s when Pierre Philippe assembled his dataset from church records, Ile aux Coudres had not yet gone through this transition.

Copies of the records from parishes throughout Quebec, including those from Ile aux Coudres, are kept in the archives of the Quebec Seminary. I wanted to see the raw data for myself, so Milot and I drove through the cobblestone streets of historic lower Quebec City and up a steep hill to the massive complex of five-story stone buildings that comprise the Archdiocese of Quebec, the central administrative branch of the Roman Catholic Church in Canada.

There we met Diocesan Archivist Pierre Lafontaine, a casually dressed middle-aged man who spoke quietly, apologizing for his English, which he rarely had occasion to use. Lafontaine led us into a large room with three tables forming a crescent, where he had set out several books in anticipation of our visit.

One of the oldest looking books had a faded red cover with gold text and elaborate patterns on the spine. Lafontaine explained that it contained the decrees issued by the Council of Trent in the middle of the 16th century. One decree specified that all Catholic parishes must keep detailed records of the major life events of its members. On the same table sat a scruffy-looking book with a hand-written label on the cover that read “De 1859 – 1866.” It contained records of the baptisms, weddings, and funerals from those years—the raw data Milot and Mayer had used.


Lafontaine then led us into a long, narrow room that resembled the stacks of a modern library, containing row after row of cataloged volumes of parish records like those we had just examined. Here was information that Milot and I could never hope to obtain for any other species than humans, the sort of data that evolutionary biologists dream of. We are accustomed to conducting expeditions to remote parts of the world to collect data on wild species in their native environments. The idea that some of the best evolutionary data could come from church archives was both astonishing and exciting.

The next morning Milot and I continued driving northeast along the edge of the Saint Lawrence. The drive became increasingly scenic as the river widened and highway 138 veered inland through rolling green hills. Milot pointed out a young bald eagle as it flew above the road, heading away from the river and into the forest. To our left was a ridge where he had once worked as a field research assistant, conducting surveys of birds in sections of forest that had recently burned. Following the signs toward Ile aux Coudres, the road veered to the right and then dropped abruptly toward the shore. The long, flat island could be easily seen across the narrow channel beneath us. There below us lived Milot’s new research subjects.

After an hour waiting in line, we drove aboard the Joseph-Savard, one of two ferries in operation on the busy Saturday morning and named for one of the original settlers on the island. Despite the river’s apparent tranquility, it was low tide, and a few rocks could be seen poking out above the surface. Swirls and ripples hinted at the strong currents that made this section of the Saint Lawrence a treacherous place to cross in smaller vessels, contributing to the historical isolation of the island’s inhabitants. It was especially dangerous in winter, when much of the river was frozen, though that was difficult to imagine on a warm summer day.

Twenty minutes later, we drove off the ferry, past a sign welcoming visitors that translates as, “Ile aux Coudres, with the rhythm of the tide.” The main road on the island is a two-lane affair that winds around the periphery of the island, variously perched atop a cliff with views that stretch across the Saint Lawrence to the hills of Charlevoix, or right up along the coast where the rising tide laps against a rocky beach. As we reached the southern end of the island, the road turned abruptly by a field of wildflowers that cascaded down the cliff to the shore below. We stopped at a small boulangerie where a pleasant-looking patio overlooks the river. Inside was a long line of people waiting to purchase bread and pastries, including a sweet Quebec specialty whose name, pets de soeurs, translates as “nun’s farts.”

How will this tug of war between evolution and culture be resolved? The short answer is that we simply do not know.

As Milot and I entered, a smiling woman approached us and introduced herself as Noëlle-Ange Harvey, the owner of the bakery. She explained in rapid French that her family has always lived on the island, and then pointed excitedly to a nearby wall with a framed black and white photo of a small girl blowing white fluffy seeds from a dandelion. The photo, she explained, was a screenshot from the first of a series of famous documentaries by Pierre Perrault about the island—and she was the little girl. She had purchased the bakery nine years ago from the family who first opened it in 1945 but, with an eye toward history, kept the original name—Boulangerie Bouchard.

The bakery was certainly doing good business with the weekend tourists, who had become a major source of income for islanders.³ Tourism to the region began back in the second half of the 19th century, as wealthy Americans looking to escape uncomfortable summers in the crowded cities of the northeast United States began visiting the Charlevoix region around Ile aux Coudres. This new source of income meant that islanders were no longer dependent on farming and fishing to make a living. The Pednault family planted an apple orchard on the island in 1918, and later opened a cider business that catered to tourists and would became one of Ile aux Coudres’ best-known products. Hotels were built, and the old mill, which used to grind the wheat into flour for islanders, became a tourist attraction.

Tourism is just one aspect of how the island has changed. By the 1960s, when the Perrault documentaries were filmed, many of the seafaring traditions of generations past had nearly been forgotten. The first film follows the reenactment of an old island tradition in which a row of wooden poles creates a fence that traps beluga whales when the tide goes out—hunting with the rhythm of the tide.⁴ Only a few of the old-timers remembered the details, but they decided to try it themselves for the sake of passing on the tradition. In the end, they captured a lone beluga and donated it to an aquarium in New York City.

Leaving the bakery, Milot and I headed south toward the village of Saint Louis at the southern end of the island. We passed a cemetery with tombstones that repeated a surprisingly short list of names—Harvey, Tremblay, Boudreault, Dufour, Pednault, Mailloux, Desgagnés—a reminder of how small this community has been. But while the entire village and its church looked much the way they did in historical photos from the early 1900s, it was clear from our brief visit that the 21st century had arrived. An old, silver-haired man sitting in a rocking chair on his front porch near the church waved to us and offered a friendly “bonjour” just as I imagine his grandfather would have 100 years ago, only now he did so after first removing his iPod headphones.

Modernization meant that the conclusions made by Milot, Mayer, and their colleagues about natural selection in humans could not be so easily extended to the people living here today. Medicine, technology, education, and other benefits of industrialized life mean that the age at which a woman has her first child today is affected by a great many factors, making it a less heritable trait than it used to be. Around the world, the average age at which women become mothers has been increasing in developed nations, rising in the U.S. from 21.4 in 1970 to 25 in 2006.⁵

The precise reasons for this rise have been debated, but at least one factor is education—when women spend more time in school, they delay starting a family.⁶ Other factors include access to birth control and better career opportunities. It seems societal pressure is encouraging women to begin having children later in life, while natural selection favors starting young.

How will this tug of war between evolution and culture be resolved? The short answer from evolutionary biologists is that we simply do not know. The incredible control we now have over our own survival and reproduction means that the interactions between our genes and our culture is more important than ever before in our species’ history.

Milot and I had to leave Ile aux Coudres the next afternoon. Before boarding the ferry, we drove back through Saint Louis, past the old stone church where Sunday mass was in progress. Just up the road, the same silver-haired man was still seated on his front porch, rocking slowly in his chair to the music from his headphones. The boulangerie was bustling with tourists, and the picnic tables overlooking the river were full. Nearby, a softball game was underway, and judging by the number of cars in the parking lot it seemed to attract a much larger crowd than the church.

Crossing the olive waters of the Saint Lawrence, Milot and I looked back at the island—different than it used to be, not as isolated, busy combining tradition and modernity in its own ways. From our perch on the ferry, navigating the once treacherous channel between the island and the mainland, what struck me most was the idea that natural selection would never stop—for people here or anywhere. Just as the tide will keep rising and falling, future generations will be born and have their own children, passing on both their genes and their culture. Our descendants will be different from us in some ways that are predictable and others that are not. After all, we are—like ants, albatrosses, and every other species on earth—a work in progress.

Scott Solomon teaches ecology, evolutionary biology, and scientific communication at Rice University. His first book, Future Humans: The Ongoing Evolution of Homo sapiens, will be published by Yale University Press in 2016.

References

1. Milot, E., et al. Evidence for evolution in response to natural selection in a contemporary human population. Proceedings of the National Academy of Sciences 108, 17040-17045 (2011).

2. Stearns, S.C., Byars, S.G., Govindaraju, D.R., & Ewbank, D. Measuring selection in contemporary human populations. Nature Reviews Genetics 11, 611- 622 (2010).

3. Ile aux Coudres tourism website: tourismeisleauxcoudres.com

4. Pour La Suite du Monde Dir. Brault, M. & Perrault, P. National Film Board of Canada, film (1962).

5. Matthews, T.J., & Hamilton, B.E. Delayed childbearing: more women are having their first child later in life. NCHS data brief 21, 1-8 (2009).

6. Rindfuss, R.R., Morgan, S.P., & Offutt, K. Education and the changing age pattern of American fertility: 1963–1989. Demography 33, 277-290 (1996).

This article originally appeared in the Winter 2015 Nautilus Quarterly. 

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