Stupid sesamoid bones…

Today, I had an osteology midterm. As midterms go it was pretty easy. There was, however, one bone that completely stumped me (and I hope, the rest of the class).

This guy. In isolation, obviously.

Give up? It’s the pisiform of a bear. This might mean nothing to you. But if you do happen to know what it is, you’re probably thinking, “That’s a dinky-ass little bone in the hand. There are tons of other bones your professor could have given to you!” You’d be right. But in other animals, it’s not so dinky. To give you some perspective:

The pisiform in the human wrist is marked with a p

One can clearly see how much larger the bear’s pisiform is relative to the rest of the hand while the other carpals and metacarpals seem about the same relative size. Even in the great apes, the pisiform varies greatly in size (with humans having BY FAR the smallest). Not bad for a little sesamoid bone. To understand why this drastic variation in size and shape, we need think about what exactly this bone is doing in the hand. At least in hominoids (us apes) the pisiform serves three major functions: it is one of the “high points” on the palmar side of the carpals for the flexor retinaculum (thus helping to create the “carpal tunnel” that all the important stuff goes through), it is the insertion point for the flexor carpi ulnaris (a muscle, one of the major flexors of the wrist), and it is the origin of the abductor digiti minimi (also a muscle. it allows you to move your pinky from side to side. so…important). In our close relatives the pisiform is long and rod-shaped instead of eponymously pea-shaped as it is in humans. This serves two major purposes for our more suspensory kin: it allows the carpal tunnel to be much larger (for the more massive digital flexors that they’re gonna need), but more importantly it allows for a more efficient lever arm for the flexor carpi ulnaris to act against. This is really important when you’re hanging from trees and perhaps trying to pull yourself up.

But why is it so large in the bear? They’re not hanging from trees by their digits that often. But think about what needs to happen if you’re walking on all fours with your palms on the ground. In order to push off from the substrate, you’re going to have to flex your wrist. And powerfully, if you’re an animal the size of a bear.

So… yeah. I probably should have not gotten it wrong, especially as it only had one articular surface. And it sure as shit wasn’t a distal phalanx of ANYTHING. But this post is to remind me, and you, to always keep the pisiform under consideration. You never know.

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Lego trebuchet part I or, What I’ve been doing with my summer vacation so far

Summer vacation for graduate students is generally not much of a vacation. Things need to get done. Things like theses. Things like moving. So as you can imagine, I’ve been pretty busy building a Lego trebuchet.

Now I know this isn’t really related to paleontology, paleoanthropology, or pop culture by any real stretch of the imagination. But it’s pretty cool and I figure it’s of some interest to geeks.

The genesis of this idea came a few weeks ago during a party at my house. And as my friends are pretty cool, conversation turned to siege engines. So my friend Chris made an attempt to build a Lego trebuchet. He ended up making a mangonel or onager of some sort (this was a party and there was a lot of drinking) that fired a projectile pretty far (it used tension from rubber bands as propulsion instead of a counterweight). I decided to take his basic plan and modify it into a working counterweight trebuchet, even though I really don’t have a clue how they work aside from playing a lot of Medieval: Total War. Turns out it’s challenging.

First I made the base structure larger and higher than his original. A lot of this was constructed with the intention of making a winch mechanism so any theoretical Lego people could lift the counterweight back into place after firing. I tried to make a proper differential to more efficiently distribute the forces involved, but it ended up not really working.

The second challenge was the trigger mechanism. I wasn’t exactly sure how to keep the big arm in place while still being able to release it at the push of a button. Or, brick, in this case. I settled on a design where a rubber band keeps tension on a right-angled brick that latches on to a little axle on the arm. If you push down on the thin 4-holed arm in the foreground of the picture, the right angle rotates back and releases the arm. It works pretty well.

Now the weight. This is the key to the whole operation. In most of these pictures I’m using a squished-up fossil rugose coral. It’s the heaviest thing I had on me that would fit in my little net. I think I’ve settled on a piece of basalt from Mt. Etna (thanks Mom!) though. It’s lighter, but it’s also a tad smaller and tends not to get stuck in the structure itself.As of right now, it doesn’t fire spectacularly. Maybe a foot or so. I took it over to Chris’ and he made a bunch of suggestions that I plan on putting into action. First, we need to raise the structure just a little bit to give the weight room to swing. Second, the structure and main axis of rotation needs to be stabilized. Third, and perhaps most important, the projectiles need to be in a long sling that can go taut but also releases at a very specific time (instead of a bowl that simply flings a projectile, like a catapult). This essentially increases the length of the arm, swinging the projectile in a much larger radius. The analogy that springs to my mind immediately is an atlatl.

Anyway, so that’s the trebuchet so far. Changes will be made, things will be fired, Lego castles will be destroyed.

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My problem with statistics

I’ve been wondering for a while now, and some articles that my advisor gave me to read only makes this suspicion even stronger – is the null hypothesis really worth anything?

For those not in the know, a null hypothesis is something that is drilled into budding scientists (Also, when do I get to call myself a scientist? Do I have to be published?) as practically the ONLY way to properly investigate ANYTHING. If you’re wondering about the relationship between two sets of observed phenomena, say… phalangeal length and phalangeal curvature (to give you an example from my thesis) and you think that one may have an effect on the other, well you can’t really PROVE that, can you? Instead you offer up a converse statement – that phalangeal length and phalangeal curvature have nothing to do with one another, and go ahead and test that. One of the first things I don’t like about this is the implicit assumption that the null hypothesis is somehow more acceptable. I understand that is this at least sort of guarding against bias – despite our best efforts, scientists are human and often “want” our hypothesis to be true. So essentially what we’re trying to do is find enough evidence to reject the null hypothesis. And how do we do that? With statistics!

In my master’s thesis, I contend that biomechanical evidence suggests that there should be a link between phalangeal length and curvature (and body mass and curvature, because why not?), at both an intra and interspecific level. And even if I find a correlation, if the confidence interval is below 95%, (or rather below 0.05) I am more or less forced to admit that there is no correlation. A confidence interval is a way of determining if the correlation that I found is due to random chance or not, because of course I’m not looking at every anthropoid that ever existed, I’m only measuring at most 200 individuals (I wish!) which is a miniscule fraction of the amount of animals that actually exist.

I remember my frustration at this a few years ago when I first started to read scientific papers. I had talked myself into a pretty sweet class at UMBC called “Physiological Bases of Behavior” that was essentially a literature review course. I was doing a presentation on the biology of meerkat social structure, and it appears that the alpha female in meerkat groups actually become slightly bigger after they’ve gotten alpha status. Not just in weight, but in length and skull width. However, in neither case was the difference “significant,” though if I remember correctly it was pretty close. This sort of bothered me, especially because I started to think about the evolution of eusociality in meerkats when compared with naked mole rats (where the alpha females DO have a statistically significant difference in size after they achieve alpha status – MASSIVELY so). What did the statistical significance of the size difference look like early in mole rat eusociality? It was probably not statistically significant, but it was still evolutionary significant, wasn’t it?



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What should everyone know about paleontology?

This post has been circulating among nerds today, and it’s a really great one. It’s written by Thomas Holtz, a world-renowned expert on tyrannosaurids, and was first posted on the Dinosaur Mailing List in response to a question. A number of other blogs have reprinted it, so if you want to read it (you really should) go to Archosaur Musings or Sauropod Vertebrae Picture of the Week. I was lucky enough to take a class from Dr. Holtz in one of my post-bacc semesters at the University of Maryland and he is one of those great professors who happen to be both extremely knowledgable and an excellent communicator. This is a must-read.

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Why do this?

Last semester my colleagues and I had a pretty great conversation about why we do what we do. Not all of us do the exact same thing, mind you, (something I point out a little too often, perhaps) but we’re all getting master’s degrees in “Human Biology,” which means most of us study bones, whether in forensic, archaeological or evolutionary contexts. So… we mostly work with dead things. And this has little measurable effect on society. New findings in paleontology or archaeology don’t really matter at all, in any scheme of things.

The conversation was prompted by a class some of us had on NAGPRA and repatriation and being sensitive to the cultural feelings of others. Our professor said something to the effect of “As soon as I feel like I’m not doing good to anybody, I’m going to quit.”

Most of us seemed to disagree with him:we do what we do because we think it is cool. And that any moderate increase in human knowledge produces some good effect across society. At least, that’s how we justify it to ourselves.

A dissenting voice emerged, however. This student felt that anthropology, and physical anthropology in particular was essentially navel-gazing bullshit. Sure, applied biological anthropology can help with forensic cases or something but most of it doesn’t have any real measurable effect on society. This wasn’t what I objected to. I objected to her contrasting this with “nobler” professions like medicine or engineering. Or, hell, even those scientists who are trying to cure cancer or AIDS or something. Sure, they have a direct (mostly) positive effect on society but I argued that that most likely isn’t the reason people do those kind of things. I argue that most of them are like us: they do it because it is cool – because for whatever reason the nitty-gritty activities of those professions appeal to them. Or, in the case of researchers trying to cure a disease or something, because it is an intellectual problem that they want to solve. Much like the way David Simon portrays the detectives in The Wire. The detectives solve crimes because they want to prove themselves as smarter than the criminals. I propose that cancer researchers want to ‘beat’ cancer in a similar way.

Of course I can’t deny that I, and many of us in academia (and particularly the non-helping-people sciences), have chips on our shoulders. If a character in a film or play wants to be portrayed as ambitious and successful in film or television, they are almost always medical doctors or lawyers or business people (I’m aware of the irony in me bitching about this, for ambitious is certainly not a word that anybody would use to describe me. But I know plenty of academics who are).

So, dear readers who surely number in the tens or so, why do you do whatever it is that you do?


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Okay, so I had a month of semi-self-imposed exile from this thing. Winter break and the lead up to it were pretty fantastically busy, but now everything is okay. My thesis proposal is finished, my applications are in, and the large project that I have been working on for two years is ALMOST done. Of course, the semester starts on monday, but I suspect it’ll be a slightly less stressful one than the last.

I have a lot of stuff that I’d like to write about this semester, and I’m betting that my classes will provide some good fodder.

I did start reading The Evolution of the Human Head by Dan Lieberman a few days ago, which is proving to be totally sweet.

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physical anthropology exodus and Republican scientists

So these articles came out last week, but I’ve been out of commission for a while because of the usual end of the semester stuff, not to mention trying to finish this thesis proposal and Ph.D apps and work.

The first has to do with the fact that the American Anthropological Association (AAA) dropped the word “science” from a recent publication of their long-range plan. I don’t think this really means a whole lot in and of itself (the article, which can be found here, (though you need a NYTimes password (but you have one of those already, don’t you?)) does a really good job of putting it in context), but I can’t help but see it has a clear harbinger of the failure of American four-field anthropology. At least when it comes to physical anthropologists.

As a budding paleoanthropologist with a more-than-casual interest in general vertebrate paleontology, this doesn’t really affect me. I had no intention of joining the AAA and this only makes that solid. The question is: will there be a mass exodus of biological and physical anthropologists from the AAA? Should they have left a long time ago? How many members of the American Association of Physical Anthropologists (AAPA) are also in AAA? I guess that’s three questions.

But man, the last paragraph in the story is cold.

Dr. Dominguez denied that critical anthropologists or postmodernist thinking had influenced the new statement. She said in an e-mail that she was aware that science-oriented anthropologists had from time to time expressed worry about and disapproval of their nonscientific colleagues. “Marginalization is never a welcome experience,” she said.

Is anybody else reading a lot of schadenfreude in Dominguez’ last line? As if she’s saying “Now look who’s being marginalized, bitch.” ‘Cause that’s what it seems like to me.

And the second article, from Slate. The subheadline says that most scientists are Democrats. As it is a kind of headline, it is misleading. Only 55 percent are Democrats. 6 percent are Republicans, and the rest are unaffiliated/”don’t know.” To me, that’s the most heartening thing about that little poll. 39 percent of a certain population does not identify with either party? If there were ever a case to be made for philosopher-kings, that’s it. Now, since it’s a poll the particulars of are probably bullshit, but I’d guess that the gist is more or less the same.

The article seems to be saying that in an ideal world, there would be a roughly equal number of Republicans and Democrats among scientists, and it seems to be assigning the blame at least partly on the recent politicization of science (particularly in the realm of climate change). I think this is at least partly true – scientists are not immune to politics. But what if there were no economic or policy consequences to responding to climate change? What if the question really was just “Is the overall climate of the earth changing at a faster pace than it has in the recent past and does mankind have anything to do with it?” Would we still see as much dissent from certain politicians? Of course we wouldn’t.

I also think that we’re in a weird anomalous era where Republicans have a near  monopoly on (supposedly) religiously-based social conservatism, something that I think is anathema to many scientists. This will probably change as time goes on (one hopes).

But the author doesn’t mention the OBVIOUS solution to the problem: pay scientists more. I’m totally serious. If the average scientist had the opportunity to make as much money as the average medical doctor (a profession that has a much more equal distribution of political philosophies) I’d be willing to bet that the ideology gap would shrink.

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