Heritage Cases

As a review of the experiment so far, we analysed five H. naledi dental specimens: UW101-020, UW101-809, UW101-886, UW102b-511 and U.W. 102. We are confident these all represent different individuals. In a first round of analysis performed on a set of four specimens (UW101-020, UW101- 809, UW101-886, UW102b-511), we compared the results obtained destructively sampling an enamel fragment cut from the tooth versus micro-destructive acid etching. We found that enamel etching performed similarly to cutting in terms of ancient protein recovery. All the four specimens yielded very good protein recovery and high AMELX sequence coverage, however no AMELY-specific peptide was detected. To clarify whether (i) this result could represent the identification of four teeth originating from female individuals, or whether (ii) any of these teeth originated from a male individual whose AMELY-specific peptide signal was lost due to diagenetic degradation, we then analysed, as a possible positive control, a fifth specimen (U.W. 102, left M3 - “Neo”) previously identified as a male, based on morphological evidence. Ancient proteins from Neo’s left M3 were exclusively retrieved by acid etching, without altering its morphology and minimally altering its appearance, Fig. 1. Unexpectedly, despite the recovery of dental enamel proteins was generally good and the intensity of the AMELX peptide signal was quite high, it has not been possible to observe any AMELY-specific peptide, as instead expected from a male individual. As a conclusion, we still cannot determine whether the absence of AMELY-specific peptide is due to: (i) methodological, e.g. detection limits, (ii) biological, e.g. no expression of AMELY in H. naledi, or (iii) cultural, i.e. exclusive presence of female H. naledi individuals, reasons. In modern humans, a small percentage of males do not express AMELY, AMELY null. Depending on the population and sample size the deletion of AMELY ranges from 0.02 to 4.5 % 3–8 . Is H. naledi, or at least the H. naledi male population from Rising Star Cave, AMELY null? Is there an ‘over representation’ of female individuals within the H. naledi population at the Rising Star Cave? To put our results into perspective, 5 female assignments from 5 specimens represents a 3.125% probability under the assumption that males and females are represented in the population in equal numbers. A ~3% probability of finding 5 out of 5 females is not beyond the realms of expectation, although it is sufficiently low to merit further investigation especially when minimally destructive sampling, Fig. 1, is possible. For this reason, it would be advisable to screen a larger, highly heterogeneous, sample set of H. naledi dental specimens, to further attempt the detection of AMELY-specific peptides in H. naledi using exclusively acid etching. The negligible alteration of the enamel of each dental specimen analysed.