PDF Summary:The Sports Gene, by David Epstein

In his bestselling book The Sports Gene, David Epstein uses science to support the claim that our genes play a determining role in our success in sports. He opens by refuting the idea that enough practice is a virtual guarantee of success. He then spends the rest of the book citing research on genes and performance, taking the reader around the world and over evolutionary time, all to explain why the book’s title is an impossibility. There is no single “sports gene,” just as there is no “perfect athlete.” There are, however, fortuitous pairings of the right genes and the right circumstances in the right sports that together create the remarkable and diverse feats of athleticism that we see on the elite stage.

Our guide reorganizes the wealth of content in The Sports Gene by theme to help clarify Epstein’s major arguments. To provide more grounding, our commentary includes supplemental research as well as explanations of scientific concepts in the fields of genetics and evolution.

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When we say we have the “gene” for something, we are referring to alleles. (Epstein uses the term variant rather than allele.) Alleles are different versions of a gene that lead to differences in the way that gene is expressed. Even though they represent well under 1% of our DNA, different alleles account for the huge diversity we see in the human race. For example, we all have the ABO gene that determines our blood type. But there are different versions of the gene (alleles) that result in different blood types among people. Instead of saying that an athlete has the “right gene” for their sport, it is more accurate to say that they have the right version of a gene, or allele, for their sport.

Genes and Our Response to Training

Epstein uses studies highlighting people’s varying responses to exercise programs to illustrate the power of genes in shaping athletic careers. He discusses two studies that followed groups of people participating in cardiovascular fitness and strength-building exercise programs. The results showed that people’s genetic differences cause them to respond differently to training. Results from the cardiovascular exercise program showed that:

• The aerobic capacity of 15% of participants did not improve at all, while the aerobic capacity of another 15% improved by 50% or more. The other 70% of participants fell somewhere between these values.
• Half of the participants’ base level of fitness and their response to training could be statistically determined by studying their parents.

As Epstein explains, these results make it clear that there is a strong genetic component to how people’s bodies respond to cardiovascular training. The researchers were able to find 21 alleles (versions of a gene) that accounted for the diversity in responses to cardio training. Results from the strength training program were similar:

• 17 participants added up to 50% more muscle mass.
• 32 participants gained 25% more muscle mass
• 17 participants had no muscle gains despite identical training

Along with these results, researchers again found that those who responded the most to the training program had pre-existing genetic differences from those who did not. Epstein explains that the participants who gained 50% more muscle had more active IFG-IEa, MGF, and Myogenin genes than those who did not respond to exercise.

Epstein suggests that elite athletes likely fall into the category of people whose bodies elicit a greater response to exercise and whose genes give them a naturally more athletic starting point.

There Are Benefits to Exercise Outside of Sports Performance

There is still reason to exercise even for people who do not see performance gains despite training. Epstein notes improvements in blood pressure, cholesterol, and insulin sensitivity as benefits of aerobic training outside of sports. There are also cognitive, social, and emotional benefits to exercise for athletes and nonathletes alike. An article from the University of California, Berkely outlines several benefits of exercise that have less to do with performance on the field and more to do with overall well-being. They include:

• Greater happiness and overall satisfaction

• Less loneliness and a lower risk of depression

• A greater sense of purpose and more feelings of love, gratitude, and hope

As the article explains, this is because exercise has a powerful effect on our brains, even if we don’t see any gains in our muscles.

Single Genes Can Have a Large Impact on the Field

While researchers have only been able to identify groups of genes that influence some elements of our physiology (as seen in the examples above), the relationship between some specific genes and athletic performance is more apparent. Epstein highlights some of these genes in the book.

ACTN3 Gene: Our ratio of fast- to slow-twitch muscle fibers can determine our success in some sports. Epstein discusses two versions of the ACTN3 gene, which codes for a protein found in fast-twitch muscle fibers: the “R variant” and the “X” variant. While scientists do not know how this happens, there is a strong correlation between the R variant and sprinting speed. Tests on athletes from around the world have revealed that the X genotype is almost nowhere to be found in elite sprinters.

The SRY Gene: Epstein uses the performance difference between men and women to emphasize his assertion that genes matter in sports. Epstein explains that the Sex Determining Region Y (SRY) gene accounts for most sexual variation between men and women. It is on the Y chromosome (women have two X chromosomes). The SRY gene causes the formation of testicles, which release the testosterone that produces male characteristics in developing fetuses. Epstein credits this gene and the associated higher levels of testosterone in males as the reason male athletes are (on average) bigger, faster, and stronger than female athletes.

Epigenetics: Our environment acts on our genes

An athlete’s performance is a function of both her genes and her environment. Simply knowing the gene (or genes) that codes for a particular trait is just one piece of the puzzle in demystifying human genetics. Our internal and external environments impact the way our genetic code is expressed in the real world.

Chemical compounds and proteins within our cells attach to our genetic code and control the way our DNA is read (and thus which proteins are produced). These ‘DNA attachments’ are referred to as our epigenome. Elements of our epigenome are inherited from our parents, and some are acquired (and change) throughout our lifetime. Much of our epigenome is determined after birth. Our environment and lifestyle can change the expression of our genes. This is often called epigenetics. (The term “epigenome” falls under the epigenetics term.) A well-known example of epigenetics in daily life is the risk of skin cancer from our cells being damaged by UV radiation.

As this article from the National Library of Medicine notes, even if researchers are able to pin down the exact genes for certain athletic traits, unraveling which traits in sports have a purely genetic origin is an impossible task. Athletes will always be the product of genes and environment, or as Epstein calls it, nature and nurture.

Theme 3: The Environment Plays a Role in Sports Performance

Our environment has an impact on our genes. Since our genes play such a large role in our sports performance, Epstein argues that you cannot understand what makes an athlete successful without the context of their environment. He illustrates this point using Kenyan distance runners.

The dominance of Kenyan athletes in distance running events is one of the best-known stereotypes in sports. As Epstein explains, this well of talent mainly comes from one specific tribe within Kenya. Athletes from the Kalenjin tribe represent only 12% of the Kenyan population but 75% of its elite runners. At the time of The Sports Gene’s writing, only 17 men in the United States had ever run a marathon faster than two hours and 10 minutes. But 32 men from the Kalenjin tribe accomplished the same feat in October of 2011.

Latitude and Limb Length

Epstein’s research suggests that the environment in which Kalenjin runners’ ancestors evolved helps to explain the tribe’s exceptional running ability. The Kalenjin tribe has what anthropologists call a “Nilotic” body type, characterized by long, thin limbs. Evidence from animal and human populations shows that limbs generally become longer and thinner as you move closer to the equator. Epstein explains that this is likely due to the higher temperatures in many low-latitude environments since long limbs create a greater surface area for cooling. During long-distance running events, becoming overheated will not only decrease performance but can be dangerous.

Evolution by Natural Selection Develops Human Traits

Traits that are an advantage on the sports field may also be helpful in survival situations. Evolution by natural selection, the accepted theory of evolution in modern times, posits that traits that boost an organism’s survival and (more importantly) reproductive success will become more common in a population over time.

Advantageous traits are specific to an organism’s environment. For example, while having long, thin limbs may confer a survival advantage near the equator, Epstein notes that populations that evolved in the arctic tend to have short legs (short legs conserve heat just as long legs allow it to dissipate). The traits that help certain athletes succeed in specific sports may have helped their ancestors better survive their natural environments.

Altitude and Aerobic Capacity

Another environmental factor that likely enhances the Kalenjin’s running ability is altitude. Ancestors of the Kalenjin tribe evolved close to sea level but migrated to a higher elevation in recent evolutionary history. Today the Kalenjin live at altitude in the Rift Valley. Epstein presents research suggesting that the body’s initial response to a move to altitude is an increase in the production of hemoglobin.

Hemoglobin is the molecule that carries oxygen in our blood. Producing more hemoglobin is the body’s way of capitalizing on every molecule of available oxygen in the thinner air at altitude and is the reason athletes use altitude training to maximize aerobic capacity. The combination of sea-level ancestry and living and training in the altitude “sweet spot” for hemoglobin production (between 6,000 and 9,000 feet) likely contributes to the Kalenjin tribe’s running prowess.

Sherpas as Superathletes

Epstein reinforces the idea that no single factor, genetic or environmental, can account for an athlete’s success by pointing out that other populations living at altitude are not producing Olympic endurance athletes. Nepal has competed at the Summer Olympics since 1964 but has yet to take home a medal. If simply living or training at altitude could make someone a great endurance athlete, we would expect to see marathoners from Nepal running alongside Kenyan runners.

Natives of Nepal who work on Mount Everest as sherpas are widely regarded as superathletes in their own right. Not only have many of them made the ascent up Everest many times (a feat considered by many as a pinnacle of athletic achievement), but they do so while caring for groups of other climbers and carrying the extra weight of climbing gear on their backs. If mountaineering were to become an Olympic sport, Nepal would surely be raking in the gold medals, and Sherpas would be highlighted as athletes with a genetic makeup perfectly suited to their sport.

Theme 4: Our Culture Plays a Role in Sports Performance

An athlete’s genes, practice, and environment all play an important role in her performance. But none of these explains why athletes from certain cultures choose to specialize in specific sporting events. Epstein argues that an athlete’s culture and socioeconomic status can help explain why sport-specific talent (such as the Kenyan marathon phenomenon) tends to cluster in certain areas. He focuses on Kenyan distance running and Jamaican sprinting to highlight this point.

Epstein highlights the following factors as reasons why so many Kenyans choose to pursue a running career:

• Poverty: The average income in Kenya is $800 per year. The prize money from winning a large marathon would be a fortune for the average Kenyan runner. Even winning a local or regional race could mean more money than athletes would otherwise earn in a year.
• Inclusive training philosophy: Epstein describes an open training culture in the Kalenjin population. He notes that elite athletes often train alongside aspiring runners, who will drop in on training sessions to see how they compare. Additionally, aspiring Kenyan runners are often young adults coming into the sport for the first time. In contrast to the push in US sports culture to begin training as early as possible (before it is “too late”), Epstein notes that Kenyan runners believe that if someone has the talent and puts in the work, age is not an obstacle.
• Early “training”: One study showed that 81% of elite Kenyan runners were from low-income families and had to walk or run to school. This walking served as a form of early training and resulted in a 30% higher aerobic capacity than those who did not walk to school. The same research showed that the top runners had to walk six miles, sometimes more, to school every day.

Coupling these factors with physiology exceptionally well-suited to distance running creates a well-rounded view of why there are so many successful Kalenjin runners.

Kalenjin Runners and Exceptional Mental Toughness

An NPR article highlighting the success of Kalenjin runners offers an additional culturally-based explanation for why Kalenjin runners are so successful. The article proposes that in addition to physiological advantages, athletes from this tribe are conditioned to have an exceptionally high pain tolerance. According to the article, learning to tolerate pain is an important part of growing up in the Kalenjin tribe. The article describes pain ceremonies as a rite of passage where teenagers prove their mental toughness to the rest of the tribe. High pain tolerance is a clear advantage in a sport such as the marathon, where athletes push themselves through discomfort for hours.

Taking culture into account can paint a more well-rounded picture of why Jamaican athletes have such a strong presence in sprinting events.

• As Epstein describes it, youth track is to Jamaica what football is to the United States. High school championship track meets are even more popular than professional sporting events in Jamaica.
• All children in Jamaica are pushed to try sprinting from a young age. Young children who show potential are recruited to high schools with competitive track teams, and high school students are even sponsored by local retailers. That such an interest is taken in runners at such a young age is a testament to the cultural importance of sprinting events in Jamaica, and explains why so many athletes choose track (and sprinting in particular) over other sports.

Talented American Sprinters Choose Other Sports

According to a Gallup poll, the most popular sports (measured by viewership) in the United States are football, basketball, baseball, and soccer, in that order. Less than 0.5% of people chose track and field as their favorite sport to watch. This helps to explain why young American athletes would choose to focus on the four sports listed above instead of focusing on their speed on the track. In fact, in The Sports Gene, Epstein notes that some people worry that the growing popularity of basketball in Jamaica may draw promising athletes away from the track.

Applying The Sports Gene to Our Lives

In the Afterword of The Sports Gene, Epstein invites us to explore our unique genome by trying new sports and experiencing personal growth and discovery through a training program. As his research findings and stories show, we never know what we may be good at unless we try!

(Shortform note: These invitations convey a tone of optimism and possibility. Our takeaway from The Sports Gene should not be that we don’t have the “right” genes to excel in sports. Instead, the book invites us to explore how our own genes, environment, culture, and training interact. Perhaps the most important takeaway from The Sports Gene is that we should be patient with ourselves and others along our sports journeys. If we are open to trying new things, we will likely find a sport that feels like a “natural” fit. While we may not end up in the Olympics, understanding that our bodies are programmed to have their own strengths and weaknesses can help us identify a sport that we find personally rewarding.)