Tools and food on heat lamps: pyrocognitive sparks in New Caledonian crows?

Fire has substantially altered the course of human evolution. Cooking kindled brain expansion through improved energy and time budgets. However, little is known about the origins of fire use and its cognitive underpinnings (pyrocognition). Debates on how hominins innovated cooking focus on archaeological findings, but should also be informed by the response of animals towards heat sources. Here, we report six observations on two captive New Caledonian crows (Corvus moneduloides) contacting heat lamps with tools or placing raw food on them. The tools became singed or melted and the food had browned (and was removed). These results suggest that New Caledonian crows can use tools to investigate hot objects, which extends earlier findings that they use tools to examine potential hazards (pericular tool use), and place food on a heat source as play or exploration. Further research on animals will provide novel insights into the pyrocognitive origins of early humans.

Regulation of neuronal progenitor delamination by dynein-driven post-Golgi apical transport

Radial glial (RG) cells are the neural stem cells of the developing neocortex. Apical RG (aRG) cells can delaminate to generate basal RG (bRG) cells, a cell type associated with human brain expansion. Here, we report that this delamination is regulated by the post-Golgi secretory pathway. Using in situ subcellular live imaging, we show that post-Golgi transport of RAB6+ vesicles occurs toward the minus ends of microtubules and depends on dynein. We demonstrate that the apical determinant Crumbs3 (CRB3) is also transported by dynein. Double knockout of RAB6A/A' and RAB6B impairs apical localization of CRB3, and induces a retraction of aRG cell apical process, leading to delamination and ectopic division. These defects are phenocopied by knock-out of the dynein activator LIS1. Overall, our results identify a RAB6-dynein-LIS1 complex for Golgi to apical surface transport in aRG cells, and highlights the role of this pathway in the maintenance of neuroepithelial integrity.

Developmental Differences in Neocortex Neurogenesis and Maturation Between the Altricial Dwarf Rabbit and Precocial Guinea Pig

Mammals are born on a precocial–altricial continuum. Altricial species produce helpless neonates with closed distant organs incapable of locomotion, whereas precocial species give birth to well-developed young that possess sophisticated sensory and locomotor capabilities. Previous studies suggest that distinct patterns of cortex development differ between precocial and altricial species. This study compares patterns of neocortex neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both belonging to the taxon of Glires. We show that the principal order of neurodevelopmental events is preserved in the neocortex of both species. Moreover, we show that neurogenesis starts at a later postconceptional day and takes longer in absolute gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate that the dwarf rabbit neocortex contains a higher abundance of highly proliferative basal progenitors than the guinea pig, which might underlie its higher encephalization quotient, demonstrating that the amount of neuron production is determined by complex regulation of multiple factors. Furthermore, we show that the guinea pig neocortex exhibits a higher maturation status at birth, thus providing evidence for the notions that precocial species might have acquired the morphological machinery required to attain their high functional state at birth and that brain expansion in the precocial newborn is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation instead of increased neurogenesis. Together, this study reveals important insights into the timing and cellular differences that regulate mammalian brain growth and maturation and provides a better understanding of the evolution of mammalian altriciality and presociality.

Everted Pedicled Temporalis Fascial Flap to Augment Pedicled Pericranial Flap for Lax Duraplasty in Decompressive Craniotomy: A Cost-Effective Procedure

Decompressive craniotomy is a commonly performed surgery to relieve raised intracranial pressure. At the end of the procedure, it is the convention to cover the exposed brain by performing a lax duraplasty which allows for both brain expansion and provides protection to the underlying parenchyma. Various commercially available dural substitutes are used for this purpose. These have the drawback of being both expensive and nonvascularized. We propose a technique of using pericranium along with everted temporalis fascia (both being locally harvested vascularized pedicle flaps) that can suffice in a vast majority of cases for covering the brain.

Prey Size Decline as a Unifying Ecological Selecting Agent in Pleistocene Human Evolution

We hypothesize that megafauna extinctions throughout the Pleistocene, that led to a progressive decline in large prey availability, were a primary selecting agent in key evolutionary and cultural changes in human prehistory. The Pleistocene human past is characterized by a series of transformations that include the evolution of new physiological traits and the adoption, assimilation, and replacement of cultural and behavioral patterns. Some changes, such as brain expansion, use of fire, developments in stone-tool technologies, or the scale of resource intensification, were uncharacteristically progressive. We previously hypothesized that humans specialized in acquiring large prey because of their higher foraging efficiency, high biomass density, higher fat content, and the use of less complex tools for their acquisition. Here, we argue that the need to mitigate the additional energetic cost of acquiring progressively smaller prey may have been an ecological selecting agent in fundamental adaptive modes demonstrated in the Paleolithic archaeological record. We describe several potential associations between prey size decline and specific evolutionary and cultural changes that might have been driven by the need to adapt to increased energetic demands while hunting and processing smaller and smaller game.

Fermentation Technology as a Driver of Human Brain Expansion

Thesis Statement: The consumption of externally fermented foods acted as the initial metabolic trigger enabling hominid brain expansion. Because brain tissue is metabolically expensive, it is thought that the evolution of humans’ large brains was only possible through a concomitant reduction in the size of another expensive organ system, the gut. However, this gut reduction must have itself been made possible by dietary changes, the nature of which are still unclear. Here, we propose that the initial metabolic trigger of hominid brain expansion may have been the consumption of externally fermented foods. We define “external fermentation” as occurring outside the body, as opposed to the internal fermentation that occurs through the gut microbiome. This practice could have begun accidentally and with limited understanding, but over time, fermentation technologies may have become increasingly intentional, socially-transmitted, and culturally-reinforced. We detail the mechanisms by which external fermentation can mediate the evolution of increased brain size, as well as a reduction in gut size, by increasing the bioavailability of macro- and micronutrients while reducing digestive energy expenditure. Importantly, we calculate that the reduction in human gut size relative to modern apes is mainly due to a reduction in the colon, the site of internal fermentation. We also discuss the explanatory power of our hypothesis relative to others, including realistic plausibility in hominids with brains roughly the size of modern chimpanzees. Finally, we survey external fermentation practices across human cultures to demonstrate its viability across a huge range of environments, temperatures, and food sources. We close with suggestions for empirical tests.

An early cell shape transition drives evolutionary expansion of the human forebrain

The human brain has undergone rapid expansion since humans diverged from other great apes, but the mechanism of this human-specific enlargement is still unknown. Here, we use cerebral organoids derived from human, gorilla and chimpanzee cells to study developmental mechanisms driving evolutionary brain expansion. We find that the differentiation of neuroepithelial cells to neurogenic radial glia is a protracted process in apes, involving a previously unrecognized transition state characterized by a change in cell shape. Furthermore, we show that human organoids are larger due to a delay in this transition. Temporally resolved RNA-seq from human and gorilla organoids reveals differences in gene expression patterns associated with cell morphogenesis, and in particular highlights ZEB2, a known regulator of epithelial-mesenchymal transition and cell shape. We show, through loss- and gain-of-function experiments, that ZEB2 promotes the progression of neuroepithelial differentiation, and its ectopic overexpression in human is sufficient to trigger a premature transition. Thus, by mimicking the nonhuman ape expression in human organoids, we are able to force the acquisition of nonhuman ape architecture, establishing for the first time, an instructive role of neuroepithelial cell shape in human brain expansion.

Invariant Synapse Density and Neuronal Connectivity Scaling in Primate Neocortical Evolution

Synapses are involved in the communication of information from one neuron to another. However, a systematic analysis of synapse density in the neocortex from a diversity of species is lacking, limiting what can be understood about the evolution of this fundamental aspect of brain structure. To address this, we quantified synapse density in supragranular layers II–III and infragranular layers V–VI from primary visual cortex and inferior temporal cortex in a sample of 25 species of primates, including humans. We found that synapse densities were relatively constant across these levels of the cortical visual processing hierarchy and did not significantly differ with brain mass, varying by only 1.9-fold across species. We also found that neuron densities decreased in relation to brain enlargement. Consequently, these data show that the number of synapses per neuron significantly rises as a function of brain expansion in these neocortical areas of primates. Humans displayed the highest number of synapses per neuron, but these values were generally within expectations based on brain size. The metabolic and biophysical constraints that regulate uniformity of synapse density, therefore, likely underlie a key principle of neuronal connectivity scaling in primate neocortical evolution.

Abundant Self-Amplifying Intermediate Progenitors in the Subventricular Zone of the Chinese Tree Shrew Neocortex

During evolution, neural progenitor cells in the subventricular zone (SVZ) have fundamental functions, ranging from brain volume expansion to the generation of a six-layered neocortex. In lissencephalic animal models, such as rodents, the majority of neural progenitors in the SVZ are intermediate progenitor cells (IPCs). Most IPCs in rodents undergo neurogenic division, and only a small portion of them divide a very limited number of times to generate a few neurons. Meanwhile, in gyrencephalic animals, such as primates, IPCs are able to self-renew for up to five successive divisions. However, abundant IPCs with successive proliferative capacity have not been directly observed in nonprimate species. In this study, we examined the development of neural progenitors in the Chinese tree shrew (Tupaia belangeri chinensis), a lissencephalic animal with closer affinity than rodents to primates. We identified an expansion of the SVZ and the presence of outer radial glial (oRG) cells in the neocortex. We also found that IPCs have the capacity to self-amplify multiple times and therefore serve as major proliferative progenitors. To our knowledge, our study provides the first direct evidence of abundant IPCs with proliferative potential in a nonprimate species, further supporting the key role of IPCs in brain expansion.