What We Know for Sure

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”
– Mark Twain (maybe)

I think my favorite thing about that quote is that I’ve seen it attributed, with utter certainty, to a number of people. Will Rogers supposedly said it about Herbert Hoover — but then, maybe he was unapologetically quoting Clemens [1]. I’ve also seen claims it originated earlier, with Franklin, but it doesn’t really sound either like Big Ben or his insipid (by his own admission, I think) alter ego, Poor Richard [2].

Anyhow, sorry for the two-week absence — I was indeed busy, first with Fire School and then with helping provide medical coverage for the 24 Hours of Big Bear mountain bike race.

We were busy at the latter event, but thankfully not too busy. They camped us out a little short of mile 7 — the course itself is 12 miles long, and either relay teams or a few hardy solo bikers do indeed pedal it for 24 hours, the highest number of laps winning each category — at the bottom of a ferocious hill.

I’d had a chance to ride that hill, along with about six miles of the course, on the Friday before the race, and can attest that it’s a tricky son of a bitch. It isn’t so much that it’s steep, though a couple of sections were steep, as that it’s rocky — rocks big enough that you need to keep your speed up, for fear of one stopping you cold, but also big enough that staying on top of them is non-trivial. You basically have to aim for the biggest rocks and pedal as fast as you dare, to make sure you bounce along the top. An earlier series of downhill hairpin turns don’t help either, nor does the fact that the downhill section is so long.

I pedaled into camp Friday night, trashed, just as the sun was setting: thankful I hadn’t had to do it in the dark, or as fast as I could, like the racers. The race itself began noon Saturday, and we had a steady but slow stream of patients throughout the ensuing 24, though again we only had one who scared me — but that’s a story for another day.

We did have time to see to the betterment of our trainees; in fact I was called upon to whip up a quick navigational course for them to practice map and compass skills.

I hate doing navs courses on the fly like that; you almost always get a cluster fuck. But in the event, our newbies gave us a different kind of cluster than I was expecting — looking for their first flag, they lost a radio belonging to another search team.

Now, I want to make this clear: to the extent that they didn’t take proper care of another team’s equipment, I blame that squarely on us experienced members. We never should have let them leave camp with something that expensive — I think they’re going for $500 list — improperly secured. So in addition to the obligation of needing to recover that radio for the team’s honor, I also felt a lot of personal responsibility. When the newbies headed out to look for it, accompanied by Carl, an experienced member of the other team, as a matter of course I grabbed my pack and went with them.

Carl and the recruit who’d been carrying the aforementioned radio were trying to retrace the latter’s steps, but in literally trackless West Virginia mountain terrain, covered in greenbriar and, in some spots, rhododendron with boughs as thick as a tree’s, I was dubious that it could be done by eye. Instead, I took the right flank, started at their original jumpoff point, and tried to duplicate the compass bearing they’d been walking.

When I couldn’t get a straight answer from them about what that bearing had been, it told me something. When, as we climbed, we hit an overgrown wood road and they said they’d broken their bearing to follow it uphill, it told me something more.

We stress a very practical style of navigation in search and rescue: we seldom expect people to walk compass bearings, instead teaching them to locate their target on the map and then piece together a path from “travel routes” — trails, ravines, ridgetops, gas lines, whatever is easy to walk — that may be less direct but gets you there faster and with less fatigue, by virtue of being easier to walk than a compass bearing. But when you’re taking travel routes, you take travel routes; when you walk a bearing, you have to walk an accurate bearing. Mixing and matching doesn’t work so well.

What I figured out, by the time we climbed near the ridgetop, was that they’d been veering steadily to the right as they ascended. So that “left flank” that Carl and the newbie were still trying to reconstruct was likely to be a lot farther in my direction than theirs.

If you want to lose something, by the way, a radio isn’t such a bad choice, because for a while at least, if you call it, it will call back to you. Fair is fair, Carl’s invaluable contribution to the exercise was a low-power tone he had his personal radio programmed to deliver, making the nearby (hopefully) lost radio beep at us, but not the other radios on the net, which at that point were still in use by the medical support teams.

We’d been moving, stopping, straining to hear, then repeating for a few iterations when, as faint as you can imagine, I thought I heard beeping.

“I think I hear it,” I said.

Carl: “What direction?”

“I’m not sure; it’s too faint.”

“Let’s move uphill a bit.”

Lather, rinse, repeat.

“Still not sure, but it’s louder now.” Now the second newbie, in line to my left, also thought he heard it.

Another iteration. Much louder now, and to my right. They’d drifted so far to the right that, even adding in my guesstimation of their error to the bearing they should have walked, I’d still undershot by more than the width of our little picket line. I moved toward the noise; lying on the ground in front of me, in a thankfully clear spot of ground, was the errant radio.

“I’ve got it!”

Basically, I rock.

The whole exercise, as it turned out, was emblematic of the Twain quote: the surer we’d been about the path our beginning navigators had walked, the wider the margin by which we’d have missed our mark.

Today’s entry is an exercise in taking stock of what we know and what we don’t about how the MHC genes determine humans’ choice of mates, courtesy of Jan Havlicek and S. Craig Roberts at Charles University in Prague and the University of Liverpool, respectively.

Briefly, the proteins made by the MHC genes are master actors in the vertebrate body’s defense against infection. They help identify infected cells, among other related functions, by grabbing hold of fragments of the invading microbe and displaying those fragments on the cells’ surfaces. This “antigen presentation” both alerts the immune system to the microbe’s presence and marks the infected cells for destruction.

Over the last couple of decades, researchers have been shedding light on another, surprisingly different function of the MHC: in most vertebrates, it seems to dictate an individual odor that somehow influences mate choice. In rodents — the best-studied specie for this phenomenon — females definitely choose mates whose MHC genes are different from theirs, and the effect takes place via a more- or less-attractive odor to that particular female. One girl’s Romeo is another’s Norman Bates [3].

Havlicek’s and Roberts’ concern, though, was whether this phenomenon reaches higher up the evolutionary tree — namely, to human beings. A growing body of research indicates that MHC genes — called HLA in humans — may actually play a role in our choice of mates. “Animal magnetism” may have a very aromatic cause, and one that comes literally through the nose.

The two investigators reviewed the current literature, and found a decidedly mixed bag, with studies showing that people pick HLA-dissimilar mates, that they pick HLA-similar mates, or no HLA effect at all. But the former outnumber the latter, and our hosts believe that there really is an effect there, though one that’s maybe a bit more complicated than we’d initially expected.

One of the more interesting sets of experiments are those in which subjects are given a piece of clothing worn by members of the opposite sex and asked which ones smell the most attractive. The results vary somewhat, but tend toward the conclusion that men with HLA genes that are different than a woman’s smell better to her than men with similar HLA genes.

But thereby hangs the tale: the researchers in the different studies asked their subjects different questions, ranging from “which smells best” to “which smells ‘sexiest’” to “which smells like someone you’d want a long term relationship with.” Those are very different questions!

An interesting exception — though not one that shows up in every study — is that women who are on birth control pills reverse the trend: they pick men whose HLA genes are more similar to theirs. It’s tempting to think that the pill, which basically prevents ovulation by tricking a woman’s body into thinking she’s pregnant, is uncovering a powerful set of biological imperatives: when you mate, outbreed; but when you’re pregnant, seek out relatives, who are more likely to help you raise the child [4]. But pregnancy is a heck of a lot more complicated than the two hormones present in most pills, and post-facto evolutionary arguments can be as slippery as they are compelling.

One series of experiments I hadn’t heard of before reading this paper was those studying the HLA effects on perfume preference: it turns out that people tend to prefer similar perfumes when they have similar genes, and some researchers think that’s because we use perfumes to enhance and complement, rather than simply hide, our natural body smells.

Of course, preference is all well and good, but it doesn’t always wind up at the altar: there’s a body of evidence suggesting women like rugged he-men faces for one-night stands, but gentler faces for long-term relationships [5]. When our Euro Reviewers surveyed studies of actual mate choice, the picture got murkier, with two studies suggesting people choose dissimilar mates, one similar, and a whopping seven showing no statistically significant effect at all.

This isn’t particularly surprising, though: as I’ve said before, higher mammals don’t do anything for just one reason. It may well be that HLA-associated body odor plays an important role in mate selection, but that a number of other factors also enter into it, and they’ll tend to obscure the odor effect.

H & R raise a very interesting possibility along these lines, which comes from a study of facial preference: When you show women pictures of men’s faces, they tend to pick those more HLA-similar to them as potential long-term mates. The authors don’t mention whether this study controlled for pregnancy or birth-control use, but there’s more straightforward way in which this result can make sense: maybe we’re looking for a Goldilocks level of difference with our mates, rather than just maximizing difference.

Though we know that inbreeding can be very bad, we’ve never nailed down the idea that maximal outbreeding is necessarily good. In fact, our authors map out no fewer than four possible reasons that we may seek HLA differences, or general outbreeding, with our mates, any or all of which may be true — or not. They cite research that suggests an intermediate level of outbreeding may be best.

What emerges from the murk of insufficient data is that we may have battling preferences: our eyes tell us to seek similarity, our noses to seek difference. As in many other biological systems, the struggle between two opposed systems pushes us toward an equilibrium that maximizes benefit.

To be fair, though my account of the Affair of the Missing Handheld above is writ from a singular perspective, in retrospect I can see the friction between the contradictory set of tactics we were following may indeed have put us closer to the target than either one alone could have. I don’t think the two searchers on my left flank could have realistically retraced the newbie’s steps; but by the same token, if I’d simply tried to reproduce the bearing they were supposed to have walked I would have wound up far to the left of where we needed to be.

“All things in moderation, including moderation” — but even so, sometimes, despite what we want, what we need is a nice medium.

[1] As an interesting side note, there’s a common phenomenon of historical figures apparently, from our modern-day vantage, trying to rip off earlier writers, when in fact they were just making quotes that were so obvious to their listeners that an attribution wasn’t necessary. I’ve often wondered whether Roosevelt’s “my crowded hour” wasn’t such a quote, since it sounds very Shakespearian — but I don’t know where it appears in the Bard, if at all.
[2] Dick may have been a pratt, but Ben was the original Buckaroo Banzai — maybe not so much with the gun- and swordplay, but show me any scientist in history who was such a fucking dangerous enemy to make. He’s a hero of mine; so is Roosevelt, for that matter.
[3] I exaggerate — the effect is more subtle than that, but very real.
[4] Scary possibility: some studies suggest that women who met their mates while on birth control are more likely to be unfaithful than those who aren’t. One possibility is that the pill undermines natural mate choice, sticking you with a guy you’re less thrilled with in the long term. The other, formal mind you, possibility is that girls on the pill are tramps — not that there’s anything wrong with that, some of my best friends in grad school were tramps. God bless ’em.
[5] On the average, ladies; and I’m sure that many, many guys wouldn’t turn down a roll in the hay with, say, a Tara Reid — I’m just picking a name off the top of my head, mind you — but want a girl with more existential substance for the long haul.