This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
OK, I will start with the confession. It was me. It happened innocently enough. One night I was watching TV and Jon Stewart was on. I could not help noticing a few things, among them a little bit of sweat on his forehead making its way through his makeup. Once I saw it, it was impossible to look away. It was not a drop of sweat so much as a kind of semi-gloss. He shimmered and when he did I had a feeling of great excitement.
The thoughts were already lurking in my subconscious, but Jon Stewart’s body brought them to light. Like the Corps of Engineers fighting the mighty Mississippi, Jon Stewart’s make-up people fight against nature to hold back his sweat. But on this particular night, they lost. The levee broke and as it did, my idea began. The idea was not about Stewart in particular, but watching the lengths to which a human can go to fight perspiration made me think about what sweat is doing in the first place. Hence the new idea, which, if right, would change how we think about what is going on under Jon Stewart’s clothes and under your clothes too. The idea might be right. It might also be terribly wrong. Not knowing is, actually, for a while, the fun.
To explain, I need to give you some background on science (Don’t worry, I will get back to Jon Stewart’s front). Science is partially about the scientific method (testing and rejecting hypotheses, so as to winnow if not the truth, the truest) and partially about voodoo. Maybe you knew, maybe you did not. The voodoo is what no one talks about. The voodoo is the lightning in the storm-ridden minds of scientists. It is an inexplicable mix of chance, observation and pure who knows what [1]. It is also private.
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We tend to hear about science through the work of science journalists and/or satirical TV journalists. Sometimes against their will, scientists talk to journalists about what they have discovered. They talk about published papers and what is known or almost known. But often when you hear scientists discussing what they have “found,” they sound, well, unenthusiastic. “Yes,” they say, “it was me that discovered the…(insert slightly hard to understand detail of the living world here) and I could not be more thrilled.” But often they don’t seem thrilled. They seem bored. Maybe they are. For many scientists the real joy, that raw and yelping elation, is not in the revealed discoveries, but instead the untested ideas.
When the scientific brain creates ideas, it is a cat stalking a mouse. The mouse is the idea. One hears it first, the little feet. Or maybe a smell. Once detected, it runs around among the leaves. Meanwhile, the cat watches, titillated. Haunches bunch and tense. Feet tap ever so slightly. Then there is the moment in which the cat pounces and, with the pounce, a resolution. The science we see comes after the resolution. It is the moment in which a journalist presents a scientist and her dead mouse to the world. We do not see all of the times the mouse ran away. Nor, more importantly, do we see scientists stalking the wild mice. We do not see those thrilling moments—all fur, life and mystery—when the mouse is still out there, not yet revealed for what it is, whether world-changing revelation, bullshit, or something in between.
I want to give you a bit of that pleasure of the hunt on Jon Stewart’s forehead and other parts (especially his feet), but in doing so I need to show you the wild, untamed, idea, which is a naked process, but I will do it for you. Then we can all pounce together and see what we catch. Feel free to watch the Daily Show while you read this. It helped me.
First I want to give you the rocklike observations that, when primed with Stewart’s sweat, made me see light in the first place. See if you can get them to spark too. Maybe I have missed something obvious. This is what happens most of the time. Most of the time I later realize I have overlooked or misunderstood some well-known aspect of biology. Or maybe what seems exciting to me today is actually mundane. Or maybe I am right that there is a mystery, but I am wrong about the resolution. The clay is raw. But if I am to let you in on the process, I have to show you where I am now. Showing you an untested idea is uncomfortable (I want to read more and call more people and figure out whether the idea is good) and yet I owe it to you. You deserve to see an idea so new it has barely been considered, an idea that you too might enjoy as it runs around, or at least that you might enjoy until someone pounces on it, killing it out in the tall, wild, grass.
Here are the basics. As I’ve writtenelsewhere, our bodies are covered with other species. An inch of your skin might house hundreds of species of life. The total surface of your skin, or really anyone’s skin—from ears to anus and back out—might house thousands of species. A great number of these species eat the substances oozing out of our bodies. For example, several of the bacteria species that lives on our feet, including Staphylococcus epidermidis and Bacillus subtilis, eat leucine, an amino acid common in the sweat on our feet. When these species eat leucine, they fart isoflavic acid which smells like stinky feet [2]. The farts of B. subtilis are more awful smelling, but these two species and a handful of others, when eating leucine, all stink [3]. It is an unavoidable consequence and requires no special circumstances [4]. All of this is known and contains, in and of itself, a hint of the idea I am about to offer. You now have the flint stones. Mix them with Stewart’s oily forehead sweat. I will pause while you try to make fire.
But wait, you need one more thing. Recently I finished writing about the idea that our appendix may be a storage organ for good bacteria, a kind of old growth microbe forest (The Wild Life of Our Bodies). In writing about the appendix as nature reserve, I also found myself immersed in the broader possibility our bodies might not only host and tolerate other species but actually garden them.
OK, enough background. You know what I knew. Here is the idea: If the species on our body sometimes benefit us and sometimes cost us (depending both on the conditions and the species), natural selection might be expected to lead our bodies to evolve some control over just which species live on us, and how. It has. For example, our skin produces antibiotics such as defensins and those antibiotics are at least somewhat selective in who or what they kill [5], though this selectivity is poorly understood. The antibiotics produced on our skin are a microscopic stick exercised in order to keep the single-celled horses in line. But what if our skin (like our appendixes) also offers carrots, or if not carrots, leucine? More specifically, what if the amino acids leaking out of our cells are leaked out intentionally, to encourage the bacteria most likely to need them? What if while our conscious minds are telling us to use antibiotic wipes, our subconscious bodies are giving food to the needy trillions of cells all over our skin?
You are mostly caught up. I don’t know much more than you at this point. My idea isn’t nuclear physics, but I find it exciting. After I found out as much as is above and the wires in my brain began to sizzle a little in a fun way, I started to read up more on amino acids. I thought thousands of papers might have been written on the amino acids on our skin. Apparently not. I have just found a handful, and they are old. The papers I have found tend to indicate our skin produces many amino acids and the composition of the amino acids produced (or really leaked is a better word) differs on different parts of our bodies [6]. Most sweat is produced by the eccrine glands concentrated on our heads (for cooling) hands and feet (for what?....). The composition of amino acids in sweat is independent of what we eat. Perhaps the amino acids are independent of what we eat because our bodies are trying to favor a consistent set/amount/whatever of microbes? Maybe. Maybe not.
And then there is the issue of mastodons. Amino acids are costly, or at least historically they were. Now we can eat hot dogs to get amino acids. Once, we killed mastodons for their meat, meat made mostly of proteins, proteins made of amino acids. So why is Jon Stewart’s body (and yours too) leaking them back out, leaking back out all that hard earned mastodon juice? I haven’t done it yet, but I keep meaning to figure out what proportion of the amino acids we eat are being excreted out our skin. It could be big. Maybe you are already doing the math.
As for the resolution to this story…, none has appeared yet. Jon Stewart goes on sweating. His body is covered with both bacteria and amino acids, all of which his make-up artists lovingly daub. Maybe he is feeding his bacteria, or at least he is doing so everywhere except where his make up is most thick. Or, maybe I have missed a key paper. Maybe I have missed some obvious reality of sweat or cells or bacteria. Maybe. We are still in this idea’s storm before the calm. It looks beautiful, to me, but could be revealed to be otherwise at any moment. There are thousands, maybe millions of ideas like this one in the brains of scientists. Such ideas are the most whimsical of the joys of science, its secret wonderfulnesses. We are so ignorant. Anything is possible. And, at this stage of an idea, it can be as fun to take the idea even further before reeling it back in, which brings me to Jon Stewart’s hands and feet. I understand why Stewart’s head sweats, to cool his brain, however unusual it might be. But why do his hands and feet sweat so much? Each one of his feet produces a cup of sweat a day. It is hard to believe anyone ever died of overheating hands or feet, which leads to the second idea.
What if our hands and feet sweat more so as to feed their bacteria even more. What if those bacteria in turn help to ward off fungal infections in the very places—hands and feet—where we are most likely to be exposed to fungal or bacterial pathogens. What if our body has intentionally fortified us with microscopic forces precisely where such forces are most needed? One can find hints (or at least an excited idea maker can…) suggesting this could be right. For example, Bacillus subtilus, the stinkiest species on our feet is known to produce antibiotics capable of killing foot fungus [7].
Wait! Could this be? Could an extended consideration of Jon Stewart’s body have led us to figure out how, why and where sweat is full of amino acids? Hoorah! Jump around and pause to revel in the idea between us, an idea both naked and strange. Hoorah to the ideas! Hoorah to what remains possible to discover in this world. Hoorah to all of the undocumented moments in scientists’ private, naked lives, moments when they run around their offices shouting, to themselves, hoorah. Hoorah to all those things, and then when you are done with the hoorahs, pause, smile, wonder, tense your haunches. A naked idea can only be left to run around for a little while. Time to pounce. Let’s do it together. Martial your responses, edits, concerns about the idea and, of course, your citations to the contrary. You can even martial some data, though only do so after you have run around your office or room a couple of times “wh00ting” to yourself with joy.
Meanwhile, I will go back to watching late night TV. Who knows what else I will find. Letterman’s craggy forehead, for example, must be full of things yet to be discovered, ideas yet to be formed. Then, of course, there are the really big ecological frontiers, where even more mysteries lurk, places like the rain forests, and Jay Leno’s chin.
Notes and References:
1 - Sometimes a good nap. Other times a beer. More occasionally, well, see Kary Mullis
2 - The normal, and less offensive, smell of sweat is, in contrast, acetic acid, which is also produced by bacteria, but different species eating different amino acids as well as other compounds. Essentially all “human” odors are produced by bacteria. Armpit smell is produced by bacteria called Corynebacteria which eat compounds produced by special apocrine glands in our armpits (and also our privates). Even the smell of hair is really, well, you see where this is going, the smell of the bacteria living on our scalps and in our hair. Yet, these smells, while bacterial, have many consequences. They influence our love lives and they even, as recent research shows, are what attract or fail to attract mosquitoes. If you are particularly lovely to mosquitoes, blame it own your microbes.
3 - Ara, K. et al. (2006) Foot odor due to microbial metabolism and its control. Can. J. Microbiol. 52, 357–364
4 - Which is good, since “pull my finger” only works if you have fingers.
5 - Peschel A, Jack RW, Otto M et al. Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with l-lysine. J Exp Med 2001; 193:1067–76
6 - Hadorn, B., Hanimann, F., Anders, P., Curtius, H. C., and Halverson, R. (1967). Free amino-acids in human sweat from different parts of the body. Nature (Lond.), 215, 416.
7 - Landy, M. W., G. H., Roseman, S. B., and L. G. Colio. 1948. Bacillomycin, an antibiotic from Bacillus subtilis active against pathogenic fungi. Proc. Soc. Exp. Biol. Med. 67:539-541.
Images:Jon Stewart from BuzzAboutTV; Defense line-up from Adrian College; Sweaty palms from Sweatypalmsandfeet.net; Jay Leno's chin from Premise PUNCH Tag.
