The enigmatic origins of the human brain

Reconstructing the origin and early evolution of the snake brain

Snakes represent one-eighth of terrestrial vertebrate diversity, encompassing various lifestyles, ecologies, and morphologies. However, the ecological origins and early evolution of snakes are controversial topics in biology. To address the paucity of well-preserved fossils and the caveats of osteological traits for reconstructing snake evolution, we applied a different ecomorphological hypothesis based on high-definition brain reconstructions of extant Squamata. Our predictive models revealed a burrowing lifestyle with opportunistic behavior at the origin of crown snakes, reflecting a complex ancestral mosaic brain pattern. These findings emphasize the importance of quantitatively tracking the phenotypic diversification of soft tissues-including the accurate definition of intact brain morphological traits such as the cerebellum-in understanding snake evolution and vertebrate paleobiology. Furthermore, our study highlights the power of combining extant and extinct species, soft tissue reconstructions, and osteological traits in tracing the deep evolution of not only snakes but also other groups where fossil data are scarce.

Broca's area, variation and taxic diversity in early Homo from Koobi Fora (Kenya)

Because brain tissues rarely fossilize, pinpointing when and how modern human cerebral traits emerged in the hominin lineage is particularly challenging. The fragmentary nature of the fossil material, coupled with the difficulty of characterizing such a complex organ, has been the source of long-standing debates. Prominent among them are the uncertainties around the derived or primitive state of the brain organization in the earliest representatives of the genus Homo, more particularly in key regions such as the Broca's area. By revisiting a particularly well-preserved fossil endocast from the Turkana basin (Kenya), here we confirm that early Homo in Africa had a primitive organization of the Broca's area ca. 1.9 million years ago. Additionally, our description of KNM-ER 3732 adds further information about the variation pattern of the inferior frontal gyrus in fossil hominins, with implications for early Homo taxic diversity (i.e. one or two Homo species at Koobi Fora) and the nature of the mechanisms involved in the emergence of derived cerebral traits.

Sulci 3D mapping from human cranial endocasts: A powerful tool to study hominin brain evolution

Key questions in paleoneurology concern the timing and emergence of derived cerebral features within the human lineage. Endocasts are replicas of the internal table of the bony braincase that are widely used in paleoneurology as a proxy for reconstructing a timeline for hominin brain evolution in the fossil record. The accurate identification of cerebral sulci imprints in endocasts is critical for assessing the topographic extension and structural organisation of cortical regions in fossil hominins. High‐resolution imaging techniques combined with established methods based on population‐specific brain atlases offer new opportunities for tracking detailed endocranial characteristics. This study provides the first documentation of sulcal pattern imprints from the superolateral surface of the cerebrum using a population‐based atlas technique on extant human endocasts. Human crania from the Pretoria Bone Collection (South Africa) were scanned using micro‐CT. Endocasts were virtually extracted, and sulci were automatically detected and manually labelled. A density map method was applied to project all the labels onto an averaged endocast to visualise the mean distribution of each identified sulcal imprint. This method allowed for the visualisation of inter‐individual variation of sulcal imprints, for example, frontal lobe sulci, correlating with previous brain‐MRI studies and for the first time the extensive overlapping of imprints in historically debated areas of the endocast (e.g. occipital lobe). In providing an innovative, non‐invasive, observer‐independent method to investigate human endocranial structural organisation, our analytical protocol introduces a promising perspective for future research in paleoneurology and for discussing critical hypotheses on the evolution of cognitive abilities among hominins.

Response to Comment on "Reintroduction of the archaic variant of NOVA1 in cortical organoids alters neurodevelopment"

Maricic et al. performed an undisclosed in silico-only whole-exome sequencing analysis of our data and found genomic alterations previously undetected in some clones. Some of the predicted alterations, if true, could change the original genotype of the clones. We failed to experimentally validate all but one of these genomic alterations, which did not affect our previous results or data interpretation.