**5. Discussion**

## *5.1. Cerebellar Asymmetric Pattern*

The cerebellar asymmetry is only observed in *H. sapiens* while absent in *H. erectus* and possibly *H. neanderthalensis*. In *H. sapiens*, the cerebellar length is significantly longer on the left side, while its height, sagittal orientation, and horizontal orientation do not differ between left and right side (as illustrated in Figure 4).

Further analysis found that the petalia and cranial capacity did not influence the cerebellar length and sagittal orientation in *H. sapiens*. However, the occipital petalia is significantly related to cerebellar height and horizontal orientation in *H. sapiens*. Individuals with right occipital petalia would have high and steep orientated cerebellar on the left side (as illustrated in Figure 4). The prevalence of cerebellum contralateral to the occipital lobe is suggested to be a spatial compensation [52,53], supported by the fact that the occipital petalia can be used as a predictive sign for the transverse sinus [54]. This is not repeated in the cerebellar length and sagittal orientation, indicating that the occipital petalia only

affects the superior–inferior dimension instead of the anterior–posterior and medial–lateral dimension of the cerebellum.

**Figure 4.** Cerebellar asymmetric pattern represented by Ngandong 7, La Ferrassie 1, and modern human.

## *5.2. Cerebellar Asymmetry in the Genus Homo*

Although cerebellar expansion can be traced back to grea<sup>t</sup> apes [38], the asymmetries of the cerebellum appear quite recently in *H. sapiens,* which is absent in *H. erectus* and possibly *H. neanderthalensis*. Also, this differs from the fact that the cerebral laterality is distinguished in early hominins compared to that of the grea<sup>t</sup> apes [22,25]. We provide more evidence for the difference of evolutionary trajectories between the cerebrum and cerebellum.

A flat parietal lobe, elongated occipital lobe, and flat cerebellar lobe are thought to be unique features among Neanderthal endocasts [12]. Compared to that of Neanderthals, the endocast of modern humans is much more globular, including the parietal and the cerebellum lobe [55]. The globularity of the endocast of modern humans mainly originates from the parietal expansion rather than the cerebellum [12]. Congruent with previous studies, we find that modern humans do not differ from Neanderthals much at the cerebellar length and height (without size correction), and horizontal orientation. Our results support the idea that the tentorium cerebelli prevented the horizontal dimensions, such as the cerebellar height and horizontal orientation, from diverging greatly between Neanderthals and modern humans [12]. Meanwhile, the sagittal orientation is significantly narrower in modern humans when compared to that of Neanderthals. The small sample size of the Neanderthals aside, this may reflect a species-specific feature. If so, such difference possibly occurs during the "globularization-phase" when critical features of the human

brain were established [55]. This might provide new evidence for the different rates and timing of brain development between Neanderthals and modern humans. However, such a statement needs more study and ontogenetic evidence. We sugges<sup>t</sup> this to be related to higher cognitive abilities, such as social factors [56] and language abilities [57], that differ mostly between *H. sapiens* and Neanderthals [58].
