Challenges and Insults

What doesn’t kill you changes tradeoffs.

Recently, I was camping with llamas in Wyoming. On the long mountain hikes at unfamiliar altitude, my lungs burned from exertion. In the evenings around the campfire, amid the swirling winds, my lungs burned from wood smoke. This post explains why the first kind of burning is a Good Thing, and led to bodily improvement, but the second kind is a Bad Thing and just, well, hurt.

Most things function worse as you use them. Your pencil tip gets dull. Your battery holds a smaller and smaller charge. Your comb loses some tines.

More or less, a reasonable way to think about this is with reference to the second law of thermodynamics. Entropy increases. Absent adding energy to the system, stuff breaks down. For tools, this means they become less useful.

I’ll pack a llama…

Biological things obey the laws of thermodynamics. Those of us who are old enough that we didn’t have to google what a “pencil” is know this very well. As we age, our senses diminish, our capacities ebb, and frankly we’re tired pretty much all the time.¹

And all of that assumes normal operation. Now, add the occasional damaging incident. You take an elbow to the face during a game of capture the flag. An unfortunately placed rock on a soccer field opens a gash in your knee, ripping some cartilage. Ill-spent youth with eyes buried in books leads to premature presbyopia.² The body—and mind—can heal some dings, but over time, the damage piles up.

A Light Digression

Let’s talk about the visible spectrum for just a moment.

The electromagnetic spectrum is, in a word, vast. Radio waves can have wavelengths measured in kilometers. Gamma rays are measured in thousandths of a nanometer. For a number of reasons, including the fact that only certain wavelengths of that spectrum are bouncing around here at the surface of the Earth, natural selection led to the evolution of sensors—photoreceptors—that allow humans to detect a tiny bit of the spectrum, between 380 nanometers and 750 nanometers, give or take. We call this band “visible light.”

It’s important to bear in mind that which wavelengths are visible is a claim about human physiology—photoreceptors—not about the electromagnetic spectrum per se. Those wavelengths aren’t special in some way—they aren’t intrinsically “visible.” They are simply the wavelengths that we have the equipment to detect. So what is “visible” and what is “invisible” is a claim about human physiology, not just the electromagnetic spectrum.

This distinction is important for what is to come. In a way that is analogous to the distinction between what is visible and what is invisible, the difference is between things that insult and things that challenge has to do with our bodies and our evolutionary history, not just something about objects in the world.

Insults

Those incidents I mentioned earlier—elbows, sticks, stones, etc.—are what I’m going to refer to as “insults.” By insult I mean something that causes damage to some aspect of a biological system, reducing function, if only temporarily.

Often when we are experiencing insult, we know about it because we have mechanisms on board that measure the insulting whatever-it-is and motivate appropriate remedial action. We typically refer to this as “pain.”

I say “often” because it’s not always. Our ancestors did not evolve in a world in which damaged nuclear powerplants emitted waves of harmful radiation, so we have no evolved radiation-detection and avoidance systems. In contrast, our ancestors did evolve in a world in which fire was a threat, so getting burned hurts. Thus, we move away. You can think of our threat-detection and threat-avoidance systems as picking out particular threats in the environment. They evolved because of reliably present dangers our ancestors faced. No threat, no defense.³ You could be sitting next to something emitting a lethal dose of radiation right now and be none the wiser.⁴

It should be clear that lots of things in the world are insulting. Pretty much everything that organisms want to eat is somebody else’s body part, so plants and animals have potentially insulting defenses, such as spines, toxins, claws, and stabby teeth. The inorganic world is also threatening, with sharp rocks, steep drops, deep oceans, and so forth.

How insulting!

For the most part, when faced with bodily insult, just as predicted by the laws of thermodynamics, things get worse. A spine punctures our skin and precious bodily fluids leak out. We eat a poisonous mushroom, we lose our balance and grip on reality for a few hours. We fall off a high cliff and, well, lots of our functions are badly damaged.

We can heal from some of these insults, of course. Because of the process of natural selection, a history of insult has led to the evolution of defenses and repair systems. The miracle that is the human immune system is testimony to the prevalence of nasty pathogens throughout our evolutionary history.

When healing takes place, the body returns, if it can, to the status quo ante. It tries, as it were, to restore the prior level of functioning.⁵ Insults, as I am defining them, do not lead to improved functioning. You injure your knee playing soccer when you’re 17 and the joint is potentially compromised, a little, for decades.

Callous Tradeoffs

Now, not only do some of our evolved systems defend against threats—reducing the chance that our various functions are made worse—some of our evolved systems do a pretty spectacular thing. They get better.

Now, “improve” and “better” are tough words because, really, everything is a tradeoff. Build a bigger muscle and, sure, you’re stronger, but now your daily calorie budget went up, so you have to get more food. There are always tradeoffs.

But we have systems that improve functionality by incorporating information about use in making tradeoffs.

My favorite example is calluses and, to talk about it, I’m going to talk about another one of my favorite examples, the one used to illustrate “survivorship bias.”  The story goes that during World War II, the U.S. military wanted to add armor to their planes to protect them from enemy fire. They recorded where returning planes had sustained damage, and the initial thought was to add armor to the areas that were most commonly damaged. However, statistician Abraham Wald pointed out that this approach was flawed: The planes that returned had survived despite the damage they sustained, and the damage pattern observed on them represented the areas where a plane could take hits and still return safely. The armor, then, should be added to the undamaged areas which, if hit, led to the loss of the plane.

Calluses are a bit like this. If you’re using some tool—let’s call it a “rake”—all the time, then the friction of the rake repeatedly insults your hand due to the pressure and friction. Evolution came along and said, wait a tick. These insults are telling me that my body is repeatedly subject to friction in this region. Just like the military aircraft designers of the future, I should make some adaptive changes, reinforcing these spots. Will I lose some sensitivity there? Sure. But given the use pattern, that’s a good tradeoff: less sensitivity but more protection, right where I need it.

So that’s what happened.

Calluses illustrate that in some cases, what doesn’t kill you makes you better in terms of your tradeoff in that spot.

The natural world beyond humans provides illustrative examples. Defenses depend on your environment and the way you make your living. Consider the adaptive defenses against cold of fish residing in Arctic waters. Cod and pollock produce antifreeze proteins that act as a natural antidote to the challenging (frigid) environment in which they swim. These proteins bind to emerging ice crystals, stopping them from enlarging and damaging tissue. When winter comes and temperatures drop, the fish ramp up production of the antifreeze proteins, adapting to the deepening chill. Their physiology changes in functional response, not unlike how humans produce more hemoglobin in response to spending time at altitude.

The Good Kind of Pain

Ok, now we have all the pieces to put it together. What is the difference between insults and challenges? Both insults and challenges tend to hurt, but they have different effects on the body over time.

Let’s return to the hiking trip to Wyoming and discuss lungs.

There are lots of reasons that your lungs might hurt. Here are some:

• You’re in a fire.

• Pathogens are attacking your alveoli.

• You’ve got lung cancer.

• You’re at high altitude (where there is less oxygen).

• You’re on a taxing hike.

Now, all of these can cause discomfort or pain.

Not all pains and discomforts are created equal. That is, they could lead to damage, which might or might not be fully healed, but some of them will lead to adaptive changes in the body’s tradeoffs, which will be of potential benefit.⁶

Crucially, however, what is insulting and what is challenging is due to our evolved mechanisms. This is the same distinction as visible versus invisible parts of the spectrum: the distinction lies in what adaptations humans have, not the source of the challenge/insult per se.

The first three cases are insults: they cause damage. Sure, you can fight off the disease or leave the smoky area. You might heal back to more or less where you were before you ran into your troubles. But these insults to your lungs aren’t going to lead to improvements in your body or a change in tradeoffs, as in the callus case.

Now, what about the last two? In those cases, if you are consistently at high altitude or consistently doing difficult workouts, your body changes its tradeoffs in response. It gets “better” in the sense of changing your body, in the former case by increasing oxygen-carrying capacity, in the latter case through improvements to cardiac tissue and such.

So many challenges. (Photo by Mark Bertulfo on Unsplash)

Note that, of course, there are some offsetting costs. No change is free. It might come with an increased need for calories, some reduced functioning elsewhere, or some other tradeoff that might be hard to identify. But there’s always something.

Information Informs Tradeoffs

Why do a select number of stimuli lead to changing tradeoffs instead of simply damage, followed by healing?

The short version is that the human body has evolved to make use of certain kinds of information about what tradeoffs are best given the present environment.

You are descended from a long line of individuals who made their way through life in very different ways. Your ancestors lived in various ecosystems, at various elevations, running from various critters and toward others. Some lived in chilly highlands, others lived on humid shorelines. There was, therefore, no one single best set of design tradeoffs. Selection favored systems that responded dynamically to these environments. There’s no need to go full throttle on hemoglobin if you’re at sea level. But if you’re making your living around the Himalayas, it’s a different story. And, of course, you might well move during your lifetime.

So, there are certain kinds of insults for which we have evolved facultative adaptations: these are now better understood as challenges. Rub your skin, get a callus. Without callus-making systems and healing systems, you get your outside rubbed, you have a damaged outside. Entropy and all that. By default, an insult is going to make things worse. The only way to go the other direction is with specialized adaptations.

It’s the same story for muscles. Maybe you find yourself in the Kalahari and you are going to need to hunt by chasing critters for a few days. Gonna need stamina and good leg muscles. Maybe you’ll find yourself in the Arctic paddling a kayak all the time. Upper body strength good, worth the extra calorie cost of the muscles. But you don’t want to build the muscles in the places they aren’t needed. Upper body muscles in a leg-oriented ecology is just a waste of calories. Organisms that find themselves in the same environment all the time don’t need to adjust their settings as much because the stable environments mean that there’s likely to be some reliably optimal set of tradeoffs.

So now we see why, in humans, some stimuli are insults (which temporarily reduce function) and some are challenges (which lead to functional, adaptive changes in tradeoffs). If we have a system on board to make functional changes to the body given the damage, that’s a challenge. But some things are just insults. Breathing in the air from a fire doesn’t (as far as I know) improve our lungs’ fire-resistance.

Song lyrics notwithstanding, it might not kill us, but it also doesn’t make us stronger.

It just kinda sucks.

Coda

What about psychology? Do we have “psychological defenses,” à la Freud? Are there some things we experience that are psychological insults, harming us, without any subsequent improvement? Are there psychological analogs to physical challenges, that might be experienced as unpleasant but ultimately lead to positive change? It seems to me that there are. Learning to play a musical instrument is often experienced as effortful, but it leads to improved skills. Practicing seems to be a challenge. What are psychological insults? The other two Fossils are both trained as clinicians so this issue seems to be more properly in their wheelhouse. So, for the moment, I’m going to leave this question to them.

1. This isn’t quite right. The development of organisms from zygote to adult illustrates how evolution can use energy to improve functioning. As long as energy is added, in theory, there is no reason that senescence—deteriorating with age—is necessary, as illustrated by some species, including some fish and trees. Most species, however, do not have genes that lead to this kind of life history. One reason for this can be seen easily with the following thought experiment. Suppose a gene has two effects, a positive one early in life and a negative one later in life, of roughly the same magnitude. Because more individuals will make it to the early age to the later age, the gene can be selected despite the negative effect later in life. (See the literature on antagonistic pleiotropy for more detail). These details are not crucial to the distinction drawn here.

2. Yes, these are all autobiographical.

3. This isn’t exactly right. Defenses are designed to defend against particular Types of threats. So the specific bear that is about to eat you wasn’t present in ancestral environments, but predators with sharp teeth and appetites were present. So all of this is with the understanding that a given defense is good against a range of specific Tokens, or instances, of a threat.

4. I hope you are not.

5. The immune system is an interesting case. Because it can “learn,” it gets “better” over time. See the next section on challenge to put this into what I think is the proper perspective.

6. The closest distinction that tracks the one I’m drawing of which I am aware—and I am happy to be educated if there are others—is the in the field of exercise physiology. The concepts of "overload" and "overtraining” might capture the difference somewhat. Overload is necessary for muscle growth and performance improvement, serving as a "challenge," while overtraining leads to fatigue and decreased performance, an "insult." Exercise physiology isn’t my area so, again, I would be pleased to be corrected if I’ve gotten this wrong.