Tag Archives: evolution

Thinking in Systems

In defense of the endurance running hypothesis, part 1: how we think about evolution.

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The endurance running hypothesis is the idea that humans evolved primarily as endurance runners. The argument goes that the human physique evolved and took its shape and function from the primary adaptive pressure of persistence hunting—that of chasing down our prey until its body shuts down.

However, this hypothesis is not without its detractors. A significant amount of scientists provide an array of counterevidence to the endurance running hypothesis. (And the debate continues.)

Take for example the case of the human gluteus maximus (butt muscle). Lieberman et. al. (2006) claim that the human gluteus maximus evolved its shape and size due to endurance running.

However, another article in the Journal of Comparative Human Biology finds that the gluteus maximus grows much more in high-force sports (weightlifting) and high-impact sports (such as soccer), than it does in endurance running. In fact, they also show that the butt muscle in endurance runners is no larger than in the non-athlete population.

What I disagree with is their conclusion, which is paraphrased in the “What does this mean?” section in the image below:

“The human gluteus maximus likely did NOT evolve through endurance running, but through varied explosive and forceful activities.”

gluteus-maximus-size

My disagreements with the article (and the image) are primarily about how and why we interpret the science to mean a certain thing.

At first blush, the fact that endurance running doesn’t enlarge the gluteus maximus as much as other sports seems to detract from the idea that the muscle takes its shape from endurance running. But I think it actually adds to it.

By my analysis, these findings show that the basic, untrained shape and size of the gluteus maximus—it’s “factory specifications,” if you will—assume that it’s going to do the amounts of cutting, jumping, weightlifting, and sprinting that a habitual endurance runner might need to do. But it requires aftermarket modification to meet the (literally) outsize power and stability requirements of soccer or weightlifting.

Let’s say that a muscle evolved under a particular adaptive pressure. This means that its shape and size literally evolved to do that thing. If you take a muscle that usually doesn’t do a thing for which it evolved to do, and you ask it to do that thing, you are asking it to do something that it has prepared to do for millions of years of evolution.

In order to fit a function that it has been designed to do, the changes in shape and size that the muscle should have to undergo should be smaller, not larger. You would expect a muscle to change far more if you ask it to do something that is less aligned with its evolutionary job description.

Let’s illustrate this by looking at the arm and hand.

We probably all agree that one of the things that specifically sets us apart from our hominid cousins is the ability to coordinate the thumb with the rest of the fingers in order to grasp and manipulate objects to a high degree of dexterity. In its simplest form, this is the capability to oppose the thumb and the fingers—to make an “OK” sign with the thumb and each of the fingers of each hand.

Now let’s take a snapshot of the people who take this unique human ability to its very pinnacle: string musicians, graphic artists, etc. Their livelihood depends on the degree to which they can explore the potential of one of the major evolutionary functions of the human hand.

Compare the forearm muscles of a violinist or painter with that of a weightlifter. The weightlifter’s arms, hands, and shoulders will be much larger and more powerful. (I trust I need not cite a scientific, randomly-controlled study on the matter.) Why? Quite simple: weightlifters engage in activities that develop the body to phenomenal proportions.

But if we go by the conclusions of the article, the fact that the arm and hand get bigger through weightlifting would mean that it didn’t evolve for the kind of fine motor control that you produce in the arts. (Or that lifting heavy objects is its primary evolutionary role). A particularly ambitious version of this argument would be to suggest that one of the core functions of opposition is to become better able to lift heavy objects. But all these suppositions break down when you realize that our primate cousins were not only quite able to grasp branches and use them ably, but that opposition emerges at the same time that hominid arms were becoming smaller (and less powerful), not larger (and more powerful).

Of course, the human hand (and upper extremity in general) still needs to be able to grow and develop in order to be able to lift heavy objects—and can indeed grow to a huge degree to exhibit that function. But its core evolutionary function is to produce the unparalleled dexterity of the human being.

Furthermore, the fact that the non-painter’s hand remains relatively unchanged in size compared to the painter’s hand means that the non-painter’s hand is already relatively set up to perform that kind of dextrous function—because that’s what it presumably evolved to do. This should serve as evidence (not counterevidence) that the hand is primarily for painting (and other fine motor tasks), not for weightlifting.

We should think the same of the gluteus maximus.

Let me conclude by saying that nothing I’ve written here means that the gluteus maximus evolved exclusively for endurance running. Indeed, there is ample evidence suggesting that the architecture of the gluteus maximus is uniquely multifunction as far as muscles go. (In future posts, I’ll delve more into the nuanced view of the gluteus maximus that I proposed above: that it owes its shape and size to the fact that it is a muscle designed for the kinds of “varied explosive and forceful activities” that a bipedal, primarily endurance running animal expects to have to do.)

But what we can say is that the fact that the gluteus maximus gets bigger through a particular stimulus has no bearing on its core evolutionary role, (or on the evolutionary story of the organism as a whole).

Defining our Terms, Linguistic Traps

Knowledge, “the tyranny of ethnography,” and our personal athletic horizons.

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Our athletic potential is based largely on the biological traits humans acquired in evolutionary time, while our athletic horizons are mostly built around our experience of the athletic feats of people in our society. We are not in a position to make judgments about our own athletic potential.

Daniel Lieberman, the chief proponent of the endurance running hypothesis, has continually fielded criticisms that humans could not have evolved as endurance runners, because the cognitive burdens of persistence hunting, such as the need for tracking, would have been too great for early hominids to bear (among other things).

In a 2007 paper, Lieberman et. al. respond to such criticisms suggesting that (among other things), “less-encephalized mammals than humans”—i.e. those with smaller brains—are quite capable trackers, etc. Throughout the paper, the authors suggest that such criticisms come from the observation of modern hunter-gatherer groups, such as the Bushmen. They point out that spears and other hunting techniques are relatively recent inventions (from the early stone age), which fundamentally altered the ways in which humans hunted and scavenged.

Continue reading Knowledge, “the tyranny of ethnography,” and our personal athletic horizons. →

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Running in the heat (Part 1)

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Here, I begin to answer a comment from this post, by Liliana Gutierrez Mariscal:

What makes running difficult for me?

Running in the heat

No matter what you do, it will be more difficult to run in the heat than in cool weather. But if you do take the time and trouble to run in the heat, it’ll really be worth your while.

I’ll devote another blog post to a very innovative idea that’s been put forth by a wealth of authors and scientists: the idea that we evolved into what we are now by chasing down four-legged animals in the heat of the african desert, (in other words, that we are desert endurance runners). But let’s not be tricked into thinking that achieving that level of expression will be an easy task.

Suppose we truly did evolve for the purpose of being runners, and more importantly, thanks to that activity. That being the case, we can make the argument that, running in hot weather in particular constitutes a very important part of the physical and physiological (and no doubt cognitive and emotional) expression of a human being.

Perhaps one of our most natural forms of expression (if not the most natural) is to run in the heat.

This argument comes from an evolutionary-systemic point of view. If you use a particular system for the very activity that it was developed to do in the first place (by first making it capable of operating at that level), then that system is very likely to manifest functions (or an efficiency of function) that it can’t express by performing any other activity.

Ultrarunning—the sport of putting the body through an irresponsible amount of miles—may tap into that level of expression. We already know that people sign up to run across the Sahara Desert, Death Valley, or to do back-to-back marathons in the desert summer as is the case with the Comrades Marathon.

But you don’t need to look that far for some idea that running was not created equal to other sports: Answer in the comments if you’d ever heard of a “golfer’s high,” or a “cyclist’s high.” It’s not that these cognitive states don’t happen in those sports. But the associations between running and favorable cognitive states are that much higher. They are so high, in fact (or so I argue), that people still sign up by the hundreds of thousands to run 26.2 miles despite the near-certainty that they will end the day with a significant injury.

Why do we still do it? As Christopher McDougall argues: it’s because we were born for it.

Those are the ultimate reasons for why you should run in the heat.

But I’ll give you a more proximate reason: you can make bigger gains in performance. I’m going to paraphrase a chapter-long argument in Tim Noakes’ book Waterlogged: The Serious Problem of Overhydration in Endurance Sports.

There are two important numbers in this story: 98.6° Fahrenheit and 104° Fahrenheit.

The first number, 98.6°, is of course, our normal core temperature. 104° is the temperature at which the body’s functioning becomes compromised. (This is a severe emergency).

What this means is that there are still, say, 2½ degrees of “give” between normal core temperature and the temperature at which things start getting too close to the danger zone (which starts at around 101º).

Take your typical runner stepping out into 100º heat for the first time: the body feels the heat and decides that no way is it going to let core temperature rise. It’s not accustomed to that environment—and more importantly, it doesn’t have a sweating system powerful enough to bring core temperature down, in case it needs to.

The cooling system of this average runner is fighting the environment heroically, struggling for every single tenth of a degree. That has a huge metabolic cost: the cooling systems go into overdrive, and the runner experiences fatigue in order to force a reduction in activity. Maintaining core temperature at a level that the body is comfortable with has become the most important thing—far more important than athletic performance.

But as that runner continues to train in the heat, the body begins to adapt over time: its sweating mechanism becomes more powerful, its able to more effectively circulate blood from the core to the skin—and furthermore, it knows that it’s still got those 2½ degrees of “give” between normal core temperature and the 101°, where its really beginning to skirt close to the danger zone. The runner experiences incrementally less and less fatigue; running becomes easier and easier.

As sweating system becomes more powerful, the body gives itself a little bit of rope. It’s getting used to that heat, so it lets core temperature rise a tenth of a degree, then another, and another. This isn’t a problem—it’s still in the safe zone.

What’s happening? It no longer has to fight the environment to cool those three-tenths of a degree.

In other words, the body developed a more powerful cooling system, and yet, because it developed that system, it no longer needs to use it that much!

Becoming accustomed to the heat lets you increase your level of performance in two ways: you can keep exercising at a higher core temperature, and with a more powerful sweating system. Suppose you increase your metabolic rate to tax the sweating system (which has now become more powerful) just as much as you used to tax it when you had only just started running in the heat: now you’ll be running at a much greater speed—and none of this has to do with your muscle power.

This brings us back to the argument that I was making earlier: by running in the heat, you can manifest physiological functions (heat tolerance) and psychological functions (lessened fatigue) that can’t be manifested under any other conditions.

The argument I make in this post is very similar to the argument I made in yesterday’s blog post. Just like having stronger muscles makes you a faster and safer runner at the same time, having a stronger sweating system does two things, instead of just one.

All this said, training in the heat means that we’re going to be playing with dangerous forces. Too much heat really will kill us. If we do choose to train that way, let’s do so with humility and care.

This will become a recurring topic. Soon, I’ll post a few exercises and training ideas that we can use to safely develop our heat tolerance. Also, I’ll post about the physiological aspects of the human body, that make us such good heat runners.

Remember, even though running in the heat might be really difficult, in a very deep way, it is what you do. If you gain that ability, you probably won’t regret it.

Happy running!