Keeping asymmetry in perspective: A reply to Eckhardt and Henneberg

Eckhardt and Henneberg’s criticism of our analysis of craniofacial asymmetry centers on the lack of one-to-one correspondence between our landmarks and the linear measurements presented in the study by Jacob et al. (2006). This argument is a red herring: the salient topic for debate regards our findings that asymmetry in LB1 is within the normal ranges of asymmetry exhibited by African apes and humans (Baab and McNulty, 2009). These results are not contested by Eckhardt and Henneberg, who instead direct attention to differences between one of our analyses and that of Jacob et al. (2006). These differences were explicitly acknowledged in our results section (Baab and McNulty, 2009: 617). We also included a table (Baab and McNulty, 2009: Table 3) that compared measurements in both studies, so that informed readers could evaluate differences for themselves. To wit, five of the six landmarks were either identical to points used by Jacob et al. (2006) (infraorbital foramen, alare) or located in the same anatomical region and would likely reflect similar degrees of asymmetry (frontomalare temporale, M2-M3 contact, and lingual canine margin). Given our efforts to provide a transparent comparison between the two studies, we do not see the value in Eckhardt and Henneberg (2010) republishing these differences. Our substitution of porion for ‘‘maximum cranial breadth’’ is specifically criticized, because it is not ‘‘a vault measurement’’ (Eckhardt and Henneberg, 2010). In fact, the maximum breadth in LB1 is across the supramastoid region (Brown et al., 2004), as it is in many fossil hominins and in our sample of extant apes. In modern humans, however, the maximum breadth is across the parietal rather than temporal bones. We chose porion due to its proximity to the supramastoid and its appropriate correspondence across our sample of apes, humans, and fossil hominins. It is reasonable to expect that asymmetry near porion might differ from asymmetry higher up on the cranial vault, which is why we highlighted this difference between the two studies (Baab and McNulty, 2009: Table 3). Finally, we located the M2-3 contact landmark on the preserved alveolar margin, as explicitly defined in our Table 2 (Baab and McNulty, 2009); the absence of M3 in LB1 has no effect on our ability to locate this point. Eckhardt and Henneberg (2010) also reference new data on palatal rotation, measured from photographs of 55 recent aboriginal Australian crania published by Milicerowa (1955). Theoretically, this provides a comparative context against which their previously reported measurement of rotation in LB1 (4–58) can be judged. In evaluating their results, however, two relevant issues should be considered.