Predicting the year of birth by the ¹⁴C of eye lens crystallines.

<p>The year of birth of a person may be predicted from the ¹⁴C content of the eye-lens crystallines. In an over-simplistic picture the eye lens crystallines are formed at the birth year of the individual. The year of birth predicted in that way (red circles, showing only the centre value of the 95% confidence interval) is close to the actual yeat but evidently different, in particular for the oldest individuals. More accurate results are obtained by using our model, because it takes into account that the crystallines grow later in life too: The resulting predictions (black vertical bars, showing the 95% confidence interval) are in agreement with the actual values in all cases. The two ways of predicting the year of birth correspond to using the black (atmospheric) or the red (eye-lens model) curve in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001529#pone-0001529-g001" target="_blank">Fig. 1</a>, respectively. The red line shows the ideal 1∶1 ratio between the predicted and actual year of birth.</p

The petrous portion of the human temporal bone (<i>pars petrosa</i>) retains its morphology after cremation or similar intensive heat exposure, being one of the last bones of the body to burn.

<p>Here, a typical cremated petrous portion as found in cremated human remains is shown.</p

Strontium isotope ratios (87Sr/86Sr) of petrous portions and dental enamel from Tjærby (non-cremated) and Rishøj (cremated) and of residues and leachates of petrous portions from crematin grave sites in the Fraugde region.

<p>Strontium isotope ratios (87Sr/86Sr) of petrous portions and dental enamel from Tjærby (non-cremated) and Rishøj (cremated) and of residues and leachates of petrous portions from crematin grave sites in the Fraugde region.</p

Bland and Altman plot showing the “line of equality”: the line on which the values would lie if Sr levels measured in premolar enamel (pm) exactly equaled the levels measured in the otic capsule of the petrous portion (pp).

<p>The values cluster around the line of equality, thus no systematic bias is indicated. The horizontal and vertical lines indicate the upper limit for strontium levels in Denmark (0.711; the lower level is 0.708). The two individuals in the upper right quadrant are thus non-Danish, while the individuals in the lower quadrant can be assumed to be Danish. The individual in the upper left quadrant could be either, depending on whether the enamel or the petrosal value is used. The cremated individual from Rishøjen (K442/RH U2) is indicated by an arrow.</p

The otic capsule surrounding the vestibulo-cochlear organs of the inner ear is the one of the densest bone tissues in the human body and does not remodel after the age of 2.

<p>Here, the bone tissues in the inner ear are illustrated in a cross section of a petrous portion. The limit of the otic capsule is indicated by the arrow.</p

Bland and Altman plot showing the limits of agreement.

<p>The difference between the enamel and the petrosal values (var) are plotted against the mean value of the enamel and petrosal values (st mean). Again, no bias is seen. The mean difference is 0.00007 (indicated by solid horizontal line) and +/−2SD (+/−0.001076) is indicated by the horizontal dotted lines. No values lie outside these limits, indicating that measuring either the premolar enamel or the petrosal Sr isotopic ratios will give the other value within 0.001075 (2SD).</p

Plot of Sr isotope ratios for the cremated individuals.

<p>Error bars correspond to +/−2SD of the premolar enamel-petrous portion difference (0.001076) derived from the data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101603#pone-0101603-g004" target="_blank">Figure 4</a>. The individuals from the cremation graves KH HF, KH JE and OB QE can therefore be assumed to be non-local.</p

The formation of eye lens crystallines determined by ¹⁴C.

<p>Nuclear bomb tests during 1955–63 produced large amounts of ¹⁴C, which after this period has declined exponentially (thin, grey line). Comparing the amount of ¹⁴C in eye-lens crystallines (red circles, plotted as a function of the year of birth) with the atmospheric concentration in units of pmC (percent modern Carbon) has made it possible to investigate the timing of the formation process. The red curve shows the output from our resulting lens-formation model, which provides the basis for predicting the year of birth accurately (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001529#pone-0001529-g002" target="_blank">Fig. 2</a>).</p

Comparing Ancient DNA Preservation in Petrous Bone and Tooth Cementum

<div><p>Large-scale genomic analyses of ancient human populations have become feasible partly due to refined sampling methods. The inner part of petrous bones and the cementum layer in teeth roots are currently recognized as the best substrates for such research. We present a comparative analysis of DNA preservation in these two substrates obtained from the same human skulls, across a range of different ages and preservation environments. Both substrates display significantly higher endogenous DNA content (average of 16.4% and 40.0% for teeth and petrous bones, respectively) than parietal skull bone (average of 2.2%). Despite sample-to-sample variation, petrous bone overall performs better than tooth cementum (p = 0.001). This difference, however, is driven largely by a cluster of viking skeletons from one particular locality, showing relatively poor molecular tooth preservation (<10% endogenous DNA). In the remaining skeletons there is no systematic difference between the two substrates. A crude preservation (good/bad) applied to each sample prior to DNA-extraction predicted the above/below 10% endogenous DNA threshold in 80% of the cases. Interestingly, we observe signficantly higher levels of cytosine to thymine deamination damage and lower proportions of mitochondrial/nuclear DNA in petrous bone compared to tooth cementum. Lastly, we show that petrous bones from ancient cremated individuals contain no measurable levels of authentic human DNA. Based on these findings we discuss the <i>pros</i> and <i>cons</i> of sampling the different elements.</p></div

Endogenous DNA content.

<p>Each data point represent the relationship between endogenous DNA content in tooth cementum and petrous bones from the same skeleton. Red datapoints represent skeletons in which visual tooth preservation was considered to be poor (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0170940#pone.0170940.g001" target="_blank">Fig 1</a>).</p