Abduhl Wali-i-Musi, the young Somali man arrested on piracy charges for hijacking an American ship, arrived in New York earlier this week. Law enforcement officials say the pirate is 18 years old and will therefore be tried as an adult. His parents claim that he is only 16 and has no formal birth certificate. Is there a scientific way to determine the age of a human?
Yes, but it’s not too accurate, nor is it easily applied to living subjects. One of the best methods for figuring out a person’s age is to examine his or her teeth. Every day that we’re alive, each of our teeth accrues a pair of tiny lines in its enamel and dentin. Another line shows up every year in the cementum, the substance that helps keep a tooth in place. These features arise from natural, biological cycles; environmental factors like poor diet can affect the spacing between lines, but it won’t stop their cyclical recurrence. So to determine someone’s age in years, a specialist might count the cementum lines under a microscope, starting at the stress line that shows up at birth in a human’s first molar.
Identifying each and every line can be a difficult task, however. A particular sample might be eroded by tooth decay, and tooth mineralization can blur older lines. As a general rule, it’s easier to date the teeth of someone with young, fresh teeth. In practice, standard “incremental” tooth dating will only be accurate to about a year or two for a late adolescent; a 2007 study showed that the average range of error using this method for subjects across all age groups is four years.
That method would not be appropriate for the young pirate, in any case. Investigators would need to have samples of his dental tissue, which means they’d have to pull out one of his teeth. A newly developed method using a powerful X-ray synchrotron machine could theoretically be performed on a tooth in situ, but the dose of radiation it delivers would be lethal.
The FBI would not tell the Explainer what tests were used to conclude Wali-i-Musi is a legal adult, but there are a few less invasive options. Agents in a case like this might use a simple dental X-ray to look at some general features, like root translucency, color, and periodontal recession. Then they could compare the results with those gleaned from a sample of people with similar ethnic and socioeconomic backgrounds. Due to environmental factors, the error range for this sort of analysis is six to eight years. Similarly, they might check the size of his pelvis relative to his height and weight, or the state of the growth plates in his collarbone or hand, and compare them with those from people of similar backgrounds. There’s a lot of room for individual variation in these tests, too. For someone in their late teens, a holistic analysis using a variety of tests would probably have a slop of around two years on each side. In other words, there’s no objective way to verify whether the pirate is 16 or 18.
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Explainer thanks David Hunt of the Smithsonian Institute and Tanya Smith of Harvard University.