Cranial sexual dimorphism levels in modern humans: Supporting a global expansion originating in southern Africa

Abstract

AbstractModern humans are acknowledged to have expanded across Earth from Africa. Biological measures have appeared to reflect this expansion, such as genetic diversity and cranial sexual size dimorphism. Admixture is known to be an issue for using diversity to locate where the expansion set out from in Africa; using cranial dimorphism should make admixture less of an issue. Therefore, cranial dimorphism could be of importance for clarifying the origin. This study used data sourced from the Howells dataset to infer if cranial form and shape dimorphisms indicate the expansion, and understand why cranial size dimorphism looks indicative. Form and shape dimorphisms were calculated through RMET. Size dimorphism was calculated beforehand. Cranial form and shape dimorphisms increased with distance from Africa. Form dimorphism suggested an area of origin which was predominantly in Africa and marginally in Asia. For shape dimorphism, locations spanned much farther beyond Africa. Hence, cranial form dimorphism seemed to be quite indicative of the expansion, unlike cranial shape dimorphism. Form is known to feature size and shape – cranial form dimorphism may signify the expansion mainly, or only, due to cranial size dimorphism. It seemed unsettled why cranial size and form dimorphisms seem related to the expansion because it was vague whether cranial size indicates the expansion more for males than females. Previously, a collective estimate of the origin (from biological measures including cranial size dimorphism) pointed to southern Africa; in the collective estimation process, cranial size dimorphism supported the south as would cranial form and shape dimorphisms.