Asymmetries of Cerebellar Lobe in the Genus Homo

Yameng Zhang,Xiujie Wu

doi:10.3390/sym13060988

Abstract

The endocast was paid great attention in the study of human brain evolution. However, compared to that of the cerebrum, the cerebellar lobe is poorly studied regarding its morphology, function, and evolutionary changes in the process of human evolution. In this study, we define the major axis and four measurements to inspect possible asymmetric patterns within the genus Homo. Results show that significant asymmetry is only observed for the cerebellar length in modern humans and is absent in Homo erectus and Neanderthals. The influence of occipital petalia is obscure due to the small sample size for H. erectus and Neanderthals, while it has a significant influence over the asymmetries of cerebellar height and horizontal orientation in modern humans. Although the length and height of the Neanderthal cerebellum are comparable to that of modern humans, its sagittal orientation is closer to that of H. erectus, which is wider than that of modern humans. The cerebellar morphological difference between Neanderthals and modern humans is suggested to be related to high cognitive activities, such as social factors and language ability.

Highlights

Endocast, or brain endocast, is the cast made of the interior of the neurocranium of a skull [1]
While a combination of left occipital and right frontal petalia is common in modern humans and fossilized hominins and is regarded as evidence of right-handedness [22,23,24], such observations are less exaggerated or rarely consistent in great apes and other primates [15,25]
Capuchins display a leftward frontal petalia [26] while macaques show the rightward frontal petalia [27], and both were absent of a left occipital petalia

Summary

Introduction

Brain endocast, is the cast made of the interior of the neurocranium of a skull [1]. With the advances of neuroimaging technology and theoretical innovation, there is increasing study of the cerebellum regarding its morphology, function, and evolutionary changes. Studies suggest that the cerebellum shows a similar asymmetric pattern as the cerebrum (the left-occipital, right-frontal petalia), with larger anterior lobules on the right side and larger posterior lobules on the left side [36,37]. The main aim of this study is (1) to test whether certain asymmetric patterns existed within the genus Homo; (2) to find out possible factors that affected the asymmetry, and to (3) provide morphological evidence for cerebellar reorganization and cognitive increases in the genus Homo

Materials

Cerebellar Metrics

Descriptive Statistics of the Asymmetries

Description of Cerebellar Asymmetries

ANCOVA

Limitations