How did the Human Brain Evolve? Tracking Cerebral Changes in the Fossil Hominin Record Using Advanced Imaging Techniques and 3D Modelling

Understanding the evolution of the hominin brain is critical for reconstructing the emergence of human cognitive abilities. However, given the lack of direct fossilised brain tissue, palaeoneurological studies rely on cranial endocasts, replicas of the internal surface of the braincase, to infer structural changes over time. While subjective interpretations and taxonomic assumptions have limited traditional endocast analyses, recent advances in digital imaging and automated analytical methods allow for a more objective and reproducible assessment of cortical morphology. This thesis applies a taxon-free, population-based approach to the study of hominin brain evolution, integrating high-resolution imaging techniques, computational analysis, and comparative neuroanatomy to reconstruct the chronology and pattern of cerebral reorganisation. To develop a reproducible and user-independent protocol, a detailed examination of cortical sulcal imprints in extant Homo and Pan endocasts was conducted using micro-computed tomography (micro-CT) scans. Endocasts were digitally extracted, sulcal patterns were automatically detected, and a density-based approach was applied to visualise inter-individual variation. Notably, this density mapping revealed substantial overlap in sulcal imprint locations in extant Homo, particularly in historically debated regions such as the occipital lobe. These findings reinforce the importance of integrating neuroscience-based approaches into palaeoneurology to enhance anatomical precision and minimise observer bias. Building on this automated protocol, we analysed a dataset of 58 fossil hominin endocasts spanning 3.7 million years and three genera (Australopithecus, Paranthropus and Homo) to identify variation in cortical imprints across hominin taxa. Our results reveal four distinct morphotypes, reflecting key evolutionary shifts in frontal and occipital lobe organisation. A mosaic pattern of brain evolution is evident, with intermediate configurations preserved in the fossil record, suggesting that cerebral reorganisation did not occur along a single, directional trajectory. Additionally, our findings highlight regional evolutionary dynamics, including an early reorganisation of the occipital lobe in southern African hominins, in contrast to the retention of more primitive characteristics in contemporaneous eastern African populations. This variation challenges the notion of a uniform trajectory of hominin brain evolution and underscores the complexity of cerebral reorganisation within the genus Homo. This study also revisits the cortical anatomy of hominins. By systematically analysing sulcal imprint variability within early hominins and comparing it to later Homo, we provide new insights into cortical organisation and potential cognitive adaptations. In particular, our results suggest that while multiple morphs of Australopithecus occupied similar locations and Paranthropus robustus exhibited unique endocranial features, aspects of its cortical morphology were more derived than previously assumed, warranting a re-evaluation of its evolutionary significance. By bridging the disciplines of palaeontology, neuroanatomy, and digital imaging, this research enhances our ability to reconstruct hominin brain evolution with greater anatomical precision. The integration of high-resolution imaging with automated detection protocols provides a replicable framework for future studies, enabling more precise reconstructions of cerebral reorganisation in the hominin lineage. This work not only refines our understanding of cognitive evolution but also lays a foundation for further interdisciplinary research into the neural and behavioural adaptations of early hominins.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• De Jager, Edwin John

Advisor dc:contributor.advisor

• Beaudet, Amélie

• Palaeoneurology
• Virtual cranial endocasts
• Sulcal imprints
• Sulcal morphotypes
• Lunate sulcus
• Micro-CT
• Automatic sulcus detection
• Density maps
• Brain evolution
• Comparative neuroanatomy
• Australopithecus
• Paranthropus
• Homo

Licence

• https://www.repository.cam.ac.uk/bitstreams/db2284c8-daca-48e6-aad8-f7923b40de6a/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.122667

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/391584