Why We Keep Getting Faster

Hey! You may remember me from the posts about genetics in the universe of Game of Thrones. I’m thrilled to become a regular part of Mad Art Lab. I’m taking a short break from talking about Westeros to talk about real life; but I have a couple more Game of Thrones themed posts coming up.

So recently, one of my friends asked me this question: we keep breaking Olympic records. Is this because we’re evolving to be faster?

The idea that we’re evolving to be better athletes is a pretty comforting notion, right? That in a few generations everyone will be able to run a five minute mile and lift more than their body weight. Unfortunately, I had some bad news: it’s rather unlikely that breaking records means our gene pool as a species is getting better. It’s more likely due to technological and training improvements.

Let’s start with something that might have something to do with biology (notice the caveats): Why does it seem like every marathon champion in recent years comes from Kenya? Part of this is almost assuredly cultural: a country that fields world champions in a sport will funnel support back into training athletes in that sport and will get more world champions. Basically, people love winning: no shock there.

In general, though, common wisdom is that Kenyan runners have a biological advantage: they tend to train at high altitudes. At high altitudes, there is less oxygen in the air, and so your body has to change in order to keep your blood nice and healthy and red. Anyone, no matter where they were born, can climb a mountain and get used to the thin air and their body will physically change to make up for it, in some ‘good’ ways and some ‘bad’ ways. Your heart rate will speed up, your blood pressure will rise, and you get more blood flow to your brain, which basically means your body is steeped in more ‘fresh’, oxygenated blood. Your blood plasma volume decreases, and you start making more red blood cells, which means that every unit of blood has more hemoglobin and can more effectively grab oxygen from your lungs. And finally, your muscle fibers get thinner, meaning oxygen-dependent mitochondria are closer to the edge of the cell and oxygen can get to them more readily.

Can you see how someone who had more blood, with more oxygen, and muscles that used that oxygen more efficiently, would be a better runner?

Why, then, aren’t the best runners in the world from Tibet? Tibet is, after all, higher up than Kenya. And in native Tibetan populations, we see even more physiological changes, indicating that some active evolution has made these populations particularly well suited to living at high altitudes. One hypothesis is that the average man in Nairobi is taller than the average man in Lhasa. Sadly, any demographic data pertaining to African populations is incredibly hard to come by. And what with the ongoing international argument about the independent status of Tibet, that isn’t any easier. Chinese men are on average about 5’6” tall, which is pretty close to the international average, but without any data on Kenya it’s pretty useless. But that’s at least a possibility. And it would be somewhat genetic.

But here’s another thorn to throw into the argument: nutrition. Height is genetic, in general, but it’s trumped by nutrition. A lot of things work this way: there are genes that make it easier for someone to build muscle, but if you don’t eat any protein you still won’t bulk up. And there’s one really cool factoid that brings this home. When you consider first generation immigrants and their children, if the parents were tall for the town they grew up in, the children will often be tall for the town their parents immigrated to: even if the average heights in those two towns were vastly different. Basically, as we get better at feeding more people, more people can grow to their full potential, and there will be more taller people and more faster runners.

But as far as I can tell, those two things are very tightly inter-related. People noticed that runners who lived in the mountains did better, and started training in the mountains. And so everyone started getting faster. That has everything to do with how you train and nothing to do with genetics. Someone who gets a better running shoe or finds a better swim suit would have a leg up on his or her competitors as well, without meddling with anyone’s DNA. And don’t even start about the constant race between athletes who want to dope and authorities who want to shut down doping. But the biggest improvement we’re going to see in upcoming years (hopefully) could be nutrition-based: if more people have better nutrition, we as a species will be stronger and faster.

Is it possible that people are evolving to be taller, leaner, and better at marathons? Yes, but it would be hard to see with all the confounding effects that I talked about above. You would need to ask two questions: is speed at running a marathon an inherited trait? I could believe that parts of it – things like the length of your legs, the strength of your heart, and your capacity to build the right kind of muscle – were. Do fast runners generally have more children than slow runners? That’s what I’m not so certain of.