Insights into the palaeobiology of an early Homo infant: multidisciplinary investigation of the GAR IVE hemi-mandible, Melka Kunture, Ethiopia

Adeline Le Cabec,Thomas Colard,Sabine Gaudzinski-Windheuser,Gabriele Di Carlo,Catherine Chaussain,Rita T Melis,Laura Pioli,Damien Charabidze,Jean-Jacques Hublin,Fernando Ramirez-Rozzi,Margherita Mussi

doi:10.1038/s41598-021-02462-1

Abstract

Childhood is an ontogenetic stage unique to the modern human life history pattern. It enables the still dependent infants to achieve an extended rapid brain growth, slow somatic maturation, while benefitting from provisioning, transitional feeding, and protection from other group members. This tipping point in the evolution of human ontogeny likely emerged from early Homo. The GAR IVE hemi-mandible (1.8 Ma, Melka Kunture, Ethiopia) represents one of the rarely preserved early Homo infants (~ 3 years at death), recovered in a richly documented Oldowan archaeological context. Yet, based on the sole external inspection of its teeth, GAR IVE was diagnosed with a rare genetic disease–amelogenesis imperfecta (AI)–altering enamel. Since it may have impacted the child’s survival, this diagnosis deserves deeper examination. Here, we reassess and refute this diagnosis and all associated interpretations, using an unprecedented multidisciplinary approach combining an in-depth analysis of GAR IVE (synchrotron imaging) and associated fauna. Some of the traits previously considered as diagnostic of AI can be better explained by normal growth or taphonomy, which calls for caution when diagnosing pathologies on fossils. We compare GAR IVE’s dental development to other fossil hominins, and discuss the implications for the emergence of childhood in early Homo.

Highlights

Childhood is an ontogenetic stage unique to the modern human life history pattern
High-resolution synchrotron imaging allowed reassessing the diagnosis of amelogenesis imperfecta (AI) in GAR IVE
Among the arguments raised by Zilberman and colleagues[19, 30], several cannot be grounded in GAR IVE

Summary

Introduction

Childhood is an ontogenetic stage unique to the modern human life history pattern. It enables the still dependent infants to achieve an extended rapid brain growth, slow somatic maturation, while benefitting from provisioning, transitional feeding, and protection from other group members. The end of childhood is marked by the eruption of the permanent first molar (M1) at ~ 6 years of age[1], and the attainment of adult brain s ize[10] In this context, fossil teeth are especially valuable because their recovery enables comparing developmental stages between fossil hominins and modern humans and because dental hard tissues record their own growth and maturation as well as stressful events experienced by the organism[11]. A specific accentuated growth marking called the neonatal line is often identifiable in the enamel and dentine of the deciduous teeth and in the mesial cusps of the permanent first molar which start mineralizing in utero[15, 16] During both infancy and childhood, protection and food provisioning by adults of the group (parents or others) is crucial for the child’s survival. Understanding the modality and time of emergence of this unique modern life history pattern is currently one of the most debated topics in human e volution[9, 17, 18]

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