Abstract: KNM2ER 3733, a remarkably complete cranium found in 1975, bears a striking resemblance to the Homo erectus specimens from Zhoukoudian that are very much younger in age, and on this basis Walker and Leakey hold the view that Homo erectus was a morphologically stable human species over a span of at least a million years. This view needs to be tested.
A morphological comparison shows that the calvaria of Nanjing 1 resembles KNM2ER 3733 in the following features: cranial length; porion height; supramastoid breadth; cranial capacity; low cranial profile in lateral view; position of the maximum cranial breadth; frontal , parietal and occipital having a share in the sagittal cranial arc; a gracile supraorbital torus; smaller size and sagittal flatness of the parietal; higher position of temporal lines; form of upper margin of temporal squama; low, wide and strongly flexed occipit; ratio of lower to upper scale lengths of occiput; and expression of occipital torus and supratorus sulcus. In contrast, the calvariae differ in the development of supratoral sulcus of the frontal; postorbital constriction; flatness of frontal squama in the transverse plane; expression of angular torus and retromastoid process; shape of the parietal; and expression of cranial vault thickness.
The facial skeleton of Nanjing 1 differs from that of KNM2ER 3733 in upper2facial shape; upper-facial flatness; orbital shape and index; facing of lateral surface of frontal process of maxilla; roundness of nasals in transverse plane; nasal roof projection; nasal index; eversion of the lower border of malar bones; cheek height; form of inferior zygomatic-maxillary margin; position of the base of zygomatic process of maxilla; and position of malar tubercle. Nanjing 1 resembles KNM2ER 3733 in other facial features, which cover facial angle, internasal keeling, and nasal bone proportions.
In conclusion, the Nanjing 1 is similar to KNM2ER 3733 in most features of the calvaria, but very different in most features of the facial skeleton. The morphological similarity in the calvariae is diagnostic and supports the claim that KNM2ER 3733 belongs to Homo erectus. In addition, this similarity suggests an anatomical stability of some members of Homo erectus in calvaria morphology over a span of at least a million years. Unfortunately, the significance of the differences in facial skeleton of these crania is uncertain.

Key words: Nanjing 1; KNM2ER 3733; Homo erectus; Morphological stability