When the starting gun fires at the Olympic track in Rio de Janeiro, there is little doubt who will be in the lead. In the Men’s 1,500 Meters Asbel Kiprop will be up front. In the women’s 5,000 meters Almaz Ayana will run away, and she may also take the 10,000 Meters. In the marathon Helah Kiprop will push the women whereas Eliud Kipchoge will be the one to watch among the men. In the Men’s 800 Meters, David Rudisha will likely hold his title and maybe break his own world record.

In other words most of these races will be dominated by runners from, or with roots in, east Africa—namely Kenya and Ethiopia, with a few Eritreans and maybe a Ugandan also standing out. Mo Farah, currently at the top of the ranking for 10,000 meters, was born in Somalia and raised in the U.K., and now trains in the U.S. Bernard Lagat, who just won the U.S. 5,000-meter Olympic qualifier (at age 41) is Kenyan-American.

East African runners have dominated for the two decades since Kenyans started winning in the mid-1990s, followed by Ethiopians shortly thereafter. This has lead to great soul searching on the part of former distance powers like the U.S. and U.K. Yet reasons for that dominance remain hotly debated, and science has had little definitive to say about it.

The reigning theory in the West is that runners from east Africa have some evolutionary advantage over runners from other backgrounds. Because so many of the elite runners come from the Oromo ethnic group in Ethiopia and the Kalenjin tribes in Kenya, it is assumed these groups must have adaptations or environments that make them faster. Perhaps it was their pastoralist fathers and grandfathers who spent generations running after cattle. Maybe their ancestors “persistence hunted,” chasing animals until they tired and could be easily killed. It could be their longer, thinner legs or their increased lung capacity from living at relatively high altitudes. In an attempt to find answers, researchers have collected DNA from across the region. Yannis Pitsiladis, a sports physiologist and geneticist from the University of Brighton in England, recently told The New York Times, “We know genes are important. We just don’t know which ones they are.”

Garrett Ash, an exercise physiologist at the Yale School of Nursing who studied Ethiopian runners with Pitsiladis, agrees. “Based on my work, and my reading of the literature,” he says, “you can’t say there’s any ancestral genetic advantage to being born in Ethiopia. It has a very heterogeneous ancestry. That being said, you do need to pick your parents and grandparents carefully. There are certain genetic variants that are required to compete at those elite levels. Oftentimes it’s a gene–environment interaction. But there’s a lot of work to be done to see what those genes actually are.”

Another factor that has been largely overlooked, however, is the “running cultures” that have evolved in specific places within Ethiopia and Kenya. One is the Ethiopian town of Bekoji, the subject of a 2012 documentary called Town of Runners. It is a poor mountain town of about 16,000 people a few hours outside the capital, Addis Ababa. In recent years it has produced 10 Olympic gold medals, 15 world records and 34 World Championship gold medals, according to British runner and writer Declan Murray, whose book about Bekoji will be published in 2017.

This is a phenomenal success rate, considering that there are countless other towns in the region with very similar ethnic backgrounds, genetic makeup, economics and the environments—but which have not produced a single elite runner. So what makes Bekoji into Bekoji?

At the center of the town’s success is a coach named Sentayehu Eshetu, who has been nourishing local running talent for over 30 years. One of his first stars was Derartu Tulu, who took the gold medal at the 1992 Olympics in Barcelona. Since then Sentayehu has drawn more and more runners to his program. Every day at 6 A.M. the hills around Bekoji are filled with hundreds of young athletes who live there and train and dream of being the next Tirunesh Dibaba or Kenenisa Bekele (both from Bekoji). Sentayehu’s runners brought home five Olympic medals from Athens in 2004, four from Beijing in 2008 and four more from London in 2012.

As in many countries, Ethiopia’s running culture started with a notable trailblazer, whose the early success seemed to create a crop of young people who wanted to follow in his footsteps. In Ethiopia that was Adebe Bikila, who is still a folk hero today for winning the 1960 Olympic Marathon in bare feet. More recently Haile Gebrselassie’s success in the 1990s saw a running boom in his hometown of Asella. But since then, the center of that boom has moved down the road to Bekoji. “When you ask people why they got involved in running, it’s because they see these people on TV or they heard it on the radio,” says Malcolm Anderson, athletics agent and founder of Moyo Sports, a management agency with runners from Kenya, Ethiopia and the U.K. “That’s what my athletes tell me. There are so many factors as to why runners get to the level they do, but one of them is the role models, and Bekoji is a place where you see that pretty fundamentally.”

“Asella and Bekoji have historically been the most extreme examples” of such running hotbeds, says Richard Nerurkar, a former elite marathoner and organizer of the Great Ethiopian Run. He points out that there are other places where one can see a similar phenomenon, and where the runners are not ethnic Oromo. “Gebregziabher Gebremariam (the 2009 World Cross Country champion) is from Tigray, the northernmost province of Ethiopia, and in the past five years we've seen lots more world-class athletes from this province including Hagos Gebrhiwet and Atsedu Tsegay, and that's likely to continue in the years ahead.

These local wellsprings of talent, in turn, pour into a larger stream made up of over 100 officially registered running clubs, some with as many as 500 athletes, and at least as many less-formal clubs in rural areas around the country.

Kenya’s running culture was pioneered most famously by Kipchoge “Kip” Keino, who won the 1968 1,500-meter race in Mexico City. Today the culture comprises training camps and groups—many located in and around the small town of Iten, where foreign teachers arrived to work at Saint Patrick’s High School in 1976. Those teachers included Peter Foster, whose brother won the Olympic 10,000-meter bronze medal that same year, and Colm O’Connell, a young geography teacher who inherited the running program from Foster in the 1970s. Soon his runners started winning, and he has since trained athletes ranging from 1988 Olympic 1,500-meter gold medalist Peter Rono to 2012 Olympic 800m gold medalist (and world record holder) David Rudisha.

Culturally, Iten functions in a way that is similar to Bekoji: attracting a huge pool of talent while fostering fierce competition and single-minded training. Every day, hungry young runners arrive in Iten from across the region. If they are lucky—and fast—they will be accepted into a training camp. If they are luckier still, they’ll be signed by an agent for training and racing abroad. But almost all will see some of their fellow athletes rise to the world stage. “I have lost track of the number of athletes who answer my question, ‘Why did you start running?’ by telling me they listened to Haile Gebrselassie winning a race on the radio and ‘simply’ decided to start,” says Michael Crawley, a PhD student at the University of Edinburgh where he is studying the relationship between distance running and development in Ethiopia. But even more important than famous Ethiopian or Kenyan runners are the runners they know. As one coach explained to Crawley, for a runner to succeed he or she needs an “imaginary person” or “exemplary person” to offer hope.

Knowing someone who does something is always more powerful than knowing of someone who does it. This is probably a significant factor in the high numbers of elite runners from Bekoji and Iten. In a very different context, it is a phenomenon identified by University of Texas at Austin sociologists Catherine Riegle-Crumb and Chelsea Moore in a 2014 study of 20,000 high school students in the U.S., which set out to research the gender gap in females studying physics. They found that “as the percentage of females [locally] employed in STEM (science, technology, engineering and mathematics) occupations increases, the odds of girls taking physics compared to boys also increases. Put differently, schools in communities with a higher percentage of women in such fields have less of a female disadvantage in rates of physics course-taking.”

Learning from any role model is a form of “social learning,” (or in immediate cases, “observational learning”) according to Harvard University anthropologist Joe Henrich, author of The Secret to Our Success. Henrich is one of the co-authors of the “cultural niche” theory of evolution (with Robert Boyd and Peter Richerson), which argues that that social learning is the most powerful force in human evolution. It allows technical knowledge to accrue over generations without needing to be relearned every time. Individuals who collect this knowledge are awarded a form of status known as “prestige,” which is unknown in other species (where “dominance,” is the only form of status). Those who have prestige are those from whom we seek out to learn.

For several generations now, athletic training knowledge has accumulated in the Kenyan highlands. In the mid-20th century members of the Kalenjin tribes embraced British athletics whereas other tribes did not, wrote John Bale and Joe Sang in Kenyan Running: Movement Culture, Geography and Global Change. For example, Kip Keino marked out a rough track as a young boy and “maintained quantitative records of his progress from the age of 15 when his best time for the mile was five minutes and 49 seconds.” Seven years later he made his first international appearance at age 22 at the 1962 Commonwealth Games in Australia. Four years after that he won the 1,500-meter in the 1968 Olympics and took silver in the 5,000-meter.

It may be that there is some genetic advantage to being Kalenjin. But the fact that most of the great Kenya runners are from one of the Kalenjin tribes may have a cultural explanation as well, according to Benoit Gaudin of the Department of Sport Sciences at Addis Ababa University. One of his research projects involves interviewing elite non-Kalenjin runners and asking them how they gained their positions. They report that finding accommodation and joining a training camp are much more difficult if you are not Kalenjin.

Those who succeed do so by basically becoming Kalenjin. “Either they learn the language or they marry a Kalenjin girl or they have high-profile support inside the running community, and someone is helping them. Otherwise it’s very difficult, because they have their own specific language even within the Kalenjin group. For example, you can train with them today but you don’t know where the next training is tomorrow, because when it comes time to give this key information, they switch languages. If they want to close the business, they can do it very easily. They are protecting their niche. And this is very interesting because it is ethnicity, but it has nothing to do with genetics.”

To date, these sorts of explanations for east Africa’s running dominance have been largely ignored. There may well be key environmental and physiological factors, such as diet or altitude or childhood foot travel. But history offers a warning against overstating these. As Bale and Sang note, when Finnish athletes dominated the global running scene in the 1930s and ‘40s, various theories about “climatic energy” and the vast wilderness where they lived—“like animals in the forest”—were offered for their success. So as we look to explain our losses, we should be mindful that Kenya and Ethiopia may not always be on top and that the seeds of victory may well be planted elsewhere. After all, as O’Connell—who ran the running program in Iten—told David Epstein, author of The Sports Gene: Inside the Science of Extraordinary Athletic Performance, “The genes didn’t go away in Finland, the culture did.