helpful to know the sex before trying to determine the age; and since sexual characteristics differed somewhat between racial groups, it was helpful to ascertain the race before trying to determine the sex. Ancestry, sex, age.
Ancestry he already knew he had little chance of determining. Not on this assemblage of subadult bones. It might be that when he opened the sack with the skull and the mandible, he might find that the incisors were “shovel shaped,” which in this part of the world would suggest, but hardly prove, Native American ancestry. In any case he wasn’t yet ready to face that particular dismal litter of human debris. Besides, he didn’t need the race to determine the sex. He already knew the sex.
Once again, Orihuela had been on the mark. Subadult or not, the sexual characteristics of these remains were unmistakable, and they were those of a female.
The “too much chewed” right innominate bone-the right half of the pelvis-made that absolutely clear. The bones of the pelvis, for obvious reasons, offer more differentiating criteria between the sexes than any other skeletal element in the body. Indeed, the pelvis is the one skeletal element from which the sex can be determined with 100 percent reliability. Women are built to be capable of having babies. Men aren’t, and the distinctions are hard to miss or to get wrong once you know what to look for. There is the shape of the greater sciatic notch, of the obturator foramen, of the auricular surface of the ilium, of the ilium as a whole. All these things were observable despite the heavy gnawing around all the edges, and they all yelled “female” at Gideon, as they would have at anyone else who knew what he was doing.
That the skeleton of a teenage girl-thirteen to fifteen, if Orihuela was correct-should show the sexual differentiation of a woman of twenty was, as Gideon had told Marmolejo, unusual; something you didn’t expect to run into every day, or every month, and its un-commonness bothered him. Generally speaking, skeletal maturation and sexual differentiation progressed in concert. You wouldn’t expect one to outstrip the other by five years, or even three. Like any scientist, Gideon was more comfortable when his data performed the way they were supposed to, when they fit the prevailing model; and these remains definitely didn’t. However, he understood well enough that while something like this was anything but common, it wasn’t unique either, or even “abnormal.”
Human variability wandered all over the map, and, like most kinds of variability, the results were almost always in the ubiquitous form of the bell-shaped curve. Whatever characteristic you were measuring, the great majority of people could be counted on to cluster near the center, in the great, humped body of the bell. But there were always those who didn’t fit-bigger, smaller, fatter, thinner, more developed, less developed-the people with the traits that constituted the “tails” on either side of the bell, tapering down to nothing as they became more and more extreme and infrequent. What he had in front of him now was apparently an example of someone out near one of those extreme ends of the bell-shaped curve of subadult sexual differentiation. If something has, say, a one- in-a-hundred probability of occurring, then it was reasonable to expect to encounter it every hundred times or so. And he had looked at hundreds, maybe thousands, of skeletons. He was probably long past due to come across one like this.
So why worry?
But worry he did; the more extraordinary your findings, the more you had to wonder if there might be something you were misinterpreting, something more or less than met the eye, something that would easily explain away apparent discrepancies or inconsistencies. something, even, about which you were flat-out mistaken. Well, he wasn’t mistaken about the sex, of that he was sure. So that left the other end of the equation, the age. She was a subadult, all right; Gideon had already seen that for himself with a glance, but where in that category did she fit? If she were at the eighteen-year-old end, then the sexual differentiation wouldn’t be so extraordinary, no more than a year or so premature; not much to trouble oneself about. But if she were, as Orihuela had estimated, at the other end, the thirteen-year-old end…
With good reason, forensic anthropologists aren’t supposed to prefer any particular outcome of their investigations, but forensic anthropologists are as human as anybody else, and Gideon knew that the younger she was, the more his findings on sex differentiation and skeletal maturation would be at odds with each other. Bell- shaped curves notwithstanding, thirteen-year-old girls weren’t supposed to have pelvises like twenty-year-olds. There wasn’t much he could do about it except to warn himself in no uncertain terms that he was not to let what he preferred or didn’t prefer affect his analysis.
Having given himself a talking-to along these lines, he belatedly realized that his back needed a break. He got off the stool to stand up, work his shoulders, and massage the kinks out of his neck. He’d been crouched over the desk for over an hour now. Having borrowed one of the Hacienda’s vans, he had arrived at the Procuraduria a little before two, where he was received at the foot of the basement steps with full military honors-salute, clicked heels-by Donardo, the hulking cop who had been notably short on courtesies the day before. It was obvious that Marmolejo’s admonitions to Sergeant Nava had been promptly passed on down the line. Donardo had shown him to Marmolejo’s office for a cup of espresso and a leisurely chat before Gideon got down to work.
Now, wanting a breather for both body and mind, he walked down the hall to beg another coffee from Corporal Vela, Marmolejo’s adjutant, then returned with it to the bones. His aim was to come up with a probable age range of his own that would either confirm Orihuela’s estimate or refute it. The odds that he could do one or the other, and do it with confidence, were in his favor. The younger a person was, the more precisely his or her age could be determined from the skeleton. In a child under three it could often be narrowed down to a couple of months one way or the other. After thirty-five or forty, you’d have a hard time pinning it down to anything less than a ten-year range. But for a teenager, if you knew what you were doing and you had enough of the right bones in front of you (and Gideon thought he did in this case), you ought to be able to come up with a reliable-and defensible-age range of no more than three years, perhaps even two. That’s what he was shooting for.
The age of a person in her teens is established mostly by gauging the degree of growth in the long bones-the arms, legs, ribs, and collar bones. A bone grows, not simply by getting longer, but by having new bony material, epiphyses, deposited at both ends of the bone shaft. The epiphyses are made of cartilage to begin with, but with time they ossify and slowly fuse to the shaft. When the fusion is complete, the bone is done growing. And when the last epiphysis has fused to the last shaft, that’s it; you’re all “grown up.”
How long it takes from the time fusion begins until the time it’s complete and the segments are firmly, permanently attached varies from bone to bone, but for each individual bone the process moves forward through known, identifiable phases and is completed by a predictable age. Thus, by comparing the progress of fusion in the bones (there is a standard five-stage model that most anthropologists use), a fairly narrow age range can be determined with reasonable confidence-always assuming, of course, that one is working with a set of remains that aren’t too awfully far out along the tails of that bell-shaped curve. But all you can do about that is to knock on wood and hope for the best. And hedge your bets if you have any doubts. Whatever you do, however competent you are, you are going to get one wrong once in a while.
Gideon had four usable long bones to work with: the left collar bone (which might not seem to be one of the “long” bones, but is, physiologically speaking), the right femur, or thigh bone (the lower end only; the top had been chewed away), and the two bones of the lower leg: the thick, sturdy tibia and the slender fibula. Still, he thought that was enough to do the job.
He began with the clavicle, the collar bone, which he expected to give him an upper end of the age range. The clavicle is one of the last bones to fuse, the process typically not even beginning until about age eighteen. Thus, if the bone showed no evidence at all of fusion, as was indeed the case with this one, you were pretty safe in saying the individual was no older than eighteen. Okay then, as expected, she was no more than eighteen.
But he could do better than that. The leg bones develop on an earlier timetable than the clavicle does. In girls, while they vary from epiphysis to epiphysis, all of them are completely fused by the age of eighteen, when the clavicle is just getting started. But in examining the ones before him, Gideon found that, while all had begun the process of fusion, nothing was past the halfway point to completion. That meant, if the usual standards held (an appropriate place to pause for that knock on wood), that this young girl had never made it to eighteen at all, and very probably not past sixteen. So that lopped two years off the top end of the range.
What about the bottom end? As he’d just noted, all of the epiphyses of the knee and ankle joints had started on their way to attachment. But those of the knee didn’t typically even begin to attach until fifteen or so. So, if “typically” held, this girl had to be at least fifteen and was probably no more than sixteen. Orihuela had missed on that score.
Fifteen to sixteen, a two-year range, and he didn’t see how he could narrow it any more than that without really going out on a limb. He would have felt better with a seventeen-to-eighteen range, but “And why,”
