This week we publish a study on a parietal bone from Gran Dolina, Atapuerca, dated to more than 800.000 years and probably belonging to the species Homo antecessor. The general morphology suggests small dimensions and an archaic appearance, with bossing lower parietal areas (supramarginal gyrus) and flattened upper parietal areas (upper parietal lobule). The vascular network is not particularly reticulated, and it is equally developed in its anterior and posterior branches. There is a well visible parietal foramen, an accessory parietal canal, and a lot of minor vascular passages, mostly around the lambda. The bone thickness and the distribution of the diploe suggest a young age. Therefore, the information available points to a juvenile archaic human. This fragment supplies at present the only evidence on the braincase of Homo antecessor. As far as we currently know, most archaic human species do not display consistent neuroanatomical differences, apart from variation in brain size. Nonetheless, this specimen can supply valuable information if, in the future, we will be able to improve sufficiently the fossil record as to support ontogenetic series.
This week we publish a morphometric analysis of the endocranial anatomy of Buia, a skull found in Eritrea and dated to 1 million years. The cranial capacity is 995 cc. The endocast is extremely dolichocephalic: very long and narrow. Nonetheless, it shows all endocranial traits that are commonly described in “archaic humans“. The bulging occipital lobes and the vascular system resemble the Chinese specimens from Zhoukoudian. Its pronounced parietal bosses are due to a narrow cranial base and temporal areas, and not to a real enlargement of the parietal lobes. Actually, the cranial base in Buia is very narrow and flexed, and it may have influenced both the neurocranial and splanchnocranial proportions (bulging parietal surface and tall facial block). At present, there is no reason to exclude this specimen from the Homo ergaster/erectus group. The skull from Daka show a similar chronology and a similar geographic origin, although it displays much more brachycephalic proportions. If all these Afro-Asiatic archaic specimens belong to the same species, the variability is notable. It remains to be established whether the evolutionary roots of more derived taxa (like Homo heidelbergensis) can be traced back to these archaic populations, or else if Buia and Daka are still part of an undifferentiated phylogenetic group.
We have now published a study of the endocranial morphology of Maba, a Chinese fossil specimen dated approximately to the end of the Middle Pleistocene. The available portions of the upper face strongly resemble European Neandertals, like Saccopastore 1, found in Italy and supposed to have the same chronology of Maba, or Krapina 3, from Croatia. Also the spatial arrangement and the structural organization between face and braincase in Maba is reminescent of Neandertals. However, the frontal and parietal bones suggest an archaic endocranial morphology, more comparable with Homo heidelbergensis. So we have here an archaic brain form assembled onto a derived facial block. A similar situation (Neandertal traits in the face and archaic features in the vault) was also described for the sample from Sima de los Huesos (Atapuerca, Spain). If such affinity is a matter of phylogeny, the range of the paleospecies H. heidelbergensis – H. neanderthalensis should be revised, and extended to China. Otherwise, the facial Neandertal traits in this Chinese populations can be but a consequence of parallelism and analogy, and the specimen can therefore represent an archaic Asian taxon. Curiously, at the same time in Africa we have the opposite combination: Jebel Irhoud, a modern face with a Neandertal braincase! Definitely puzzling …
An amazing article has been published in Nature Physics. Brain cortical folding is influenced by genetic and physiological factors, but there are also many hypotheses concerning the possible role of mechanical forces associated with the cerebral tissues. These hypotheses are largely based on theoretical approaches and numerical simulations, integrating geometry and biomechanics. Because of the mechanical properties of cells and tissues, growth forces can be redistributed within and among the elements of the anatomical system, channeling morphogenesis and shaping the spatial organization of the anatomical components. This month Tuomas Tallinen and colleagues provide a further mathematical model of the growing cortex, introducing constraints associated with the sulcal pattern. But, more incredibly, they provide an extremely elegant and efficient experimental evidence. After MRI imaging, they prepare a physical model of the fetal brain with two gel components. The outer thin layer (simulating the cortex) swells when in contact with a solvent, undergoing a tangential expansion. When this happens, the growing outer surface and the stable inner volume must properly interact in terms of physical forces and distribution of the surface to volume adjustments. The result is amazing, because it really mimics the human cortical folding! There is an incredible correspondence between the real and simulated folding pattern, in terms of topology and degree of convolution. No programming here except the growing schedule, just physical properties, structural interaction, and forces redistribution.
“Morphology is not only a study of material things and of the forms of material things, but has its dynamical aspect, under which we deal with the interpretation, in terms of force, of the operations of energy.”
(D’Arcy Wentworth Thompson – On Growth and Form, 1942)
The Journal of Anthropological Sciences is now publishing the papers from the meeting “What Made Us Humans“, that took place in Erice on October 2014. The volume is edited by Telmo Pievani, Stefano Parmigiani and Ian Tattersall, and it includes contributions by Thomas Plummer, Dean Falk, Philip Lieberman, Jeffrey Schwartz, William Harcourt Smith, and many others. There is a section on brain and cognition, in which we publish a review on visuospatial functions and fossils. In this paper we discuss topics in extended cognition and embodiment, presenting the available sources of information from fossil anatomy: brain morphology, manipulative behaviors, and hand evolution. Modern humans displayed changes in all these traits, suggesting that differences in visuospatial integration processes may have been associated with changes of the embodying capacity, leading to derived and probably specialized relationships between brain, body, and environment. This article is a further reference on visuospatial integration and cognitive archaeology. All papers from this JASs volume are, as usually, free to download.
Paleoneurology is rarely used to test taxonomic or phylogenetic hypotheses, at least for three reasons. First, the biology and variation of many endocranial traits are not even known for living humans. Second, plesiomorph traits, parallelisms, large intra-specific variability, and subtle inter-specific differences, make this issue very difficult to test through robust quantitative approaches. Third, the paucity and fragmentation of the fossil record often hamper meaningful statistical inferences. Of course these same problems concern many other anatomical districts, and that’s why probably morphology is not always recommended as a good and reliable source of taxonomic and phylogenetic information. Despite these limits, Aurelién Mounier and his coauthors have now tried to apply cladistics to paleoneurology, taking into consideration neurocranial and endocranial traits. According to their results, at least modern humans and Neandertals can be properly characterized in terms of braincase morphology, suggesting the existence of an actual phylogenetic signal behind the patterns of endocranial variation.
We modern humans have larger parietal bones and large parietal lobes when compared with extinct human species and living apes. We also have an ontogenetic parietal bulging stage, a stage which is absent in apes and Neandertals. Interestingly, a main factor of variability in our brain morphology is the size of the precuneus, in terms of proportions and cortical surface area. Now we have compared human and chimp brains, and here it goes again: the main difference is a much larger precuneus in our species. It doesn’t look like an allometric issue, being possibly associated with that bulging stage specific of modern humans, and even absent in large-brained Neandertals. The precuneus is essential in visuospatial integration, coordinating brain, body, and environment, and bridging the somatosensorial experience with simulation and self-awareness. It is a key element to integrate space, time, and social perception. It is also worth noting that parietal lobes are particularly vascularized in our species, and the precuneus is a high-metabolic and heat-accumulating element. This may be interesting when considering that it suffers early metabolic impairments in Alzheimer’s disease, a pathology particularly associated with our species. The precuneus is also a central hub of the default mode network. Interestingly, at least in adult modern humans the size of the parietal lobes is inversely correlated with the size of the frontal and temporal lobes, introducing some phylogenetic issues on the evolution of the fronto-parietal system.
For a long time we have been looking for subtle differences between human and ape brain. This one looks not that subtle. Any functional or histological change behind this expansion, at inter-specific and intra-specific level, is still to be investigated. But most of all, it remains to be established the nature of such morphological variations. Genetic factors and selective processes cannot be excluded, but these areas are also particularly sensitive to environmental influences, including training and cultural effects.