Here a new methodological review article by Markus Bastir and his lab on tools and principles of virtual morphology, introducing and discussing geometric morphometrics, digital anatomy, laser scanning, 3D printing, programs and databases, management and logistic issues, and resources in the web. A very useful and practical primer for those interested in approaching this field!
I have just realized that Dennis Slice passed away this summer. He was one of the first pioneers in geometric morphometrics, and in particular one of those who travelled here and there to teach and explain geometric morphometrics to the first-generation of students specifically trained in shape analysis, after the introduction of the principles and programs mainly developed by him together with Bookstein, Rohlf, and Marcus. I began my journey in morphometrics with two workshops with Dennis, and then wandering between software and databases thanks to his support mail by mail. He was the mind and manager of a pioneering and everlasting morphometric internet group, and an inspiration for so many students. We anthropologists were probably the first to employ massively all those tools because, as he stressed so many times, a human skull is simply the best ever object to study with landmarks: not too small and not too large, not too regular and not too fuzzy, not too constant but not too variable, with a stable and clear geometry, and with nice borders and sutures to be used as references. That pioneering stage was rather quick, and soon most anatomy-based fields realized the amazing methodological shift introduced by geometric morphometrics. In the late 90s it was an innovation, ten years after it was the golden standard. I had a submission rejected in those very early years because – at least taking into account the reasons supplied by the journal – those methods were … too complicated for paleoanthropologists! D’Arcy Thompson proposed the basic principles of geometric morphometrics in the first half of the 20th century but, after introducing all the background of his perspective (1942), he concluded that many of those tools could not be technically developed at that time, and the aim had to be left “to other times, and to other hands”. Hands like those of Dennis Slice. Good job, Professor!
The parietal cortical association areas have increased in size and complexity in primates, and their evolution is thought to be influenced by exploratory and feeding behavior. Nonetheless, studies considering parietal lobe morphology and macroscopic anatomy among primate taxa are scarce. Cercopithecidae represent an interesting group for evolutionary studies as this primate family includes diversified species, spanning a variety of ecological strategies. Moreover, their sulcal patterns have been extensively described, and can be relatively well identified on endocasts, thus making them useful for paleoneurological studies. This week we have published a survey on parietal lobe variation in cercopithecid endocasts through geometrical models, in collaboration with Amélie Beaudet. First, we applied geometric morphometrics, using landmarks based on the main sulci limiting the major brain regions, in order to assess variations in parietal lobe proportions. Then, we further explored within-parietal morphology through deformation-based models after virtual extraction of the parietal lobe surface. The sample included 3D reconstructed endocasts from 11 genera belonging to the three main tribes, cercopithecini, papionini, and colobini.
Our landmark analysis was able to detect the main pattern of variation separating cercopithecini from colobini, with the former group displaying larger occipital lobe proportions and the latter one characterized by larger parietal proportions. Papionini tend to exhibit intermediate parieto-occipital proportions, though Papio and Theropithecus have colobin-like figures. A second pattern of variation is associated with differences in height of the parieto-occipital region. This second trait is correlated with endocranial volume, and it is probably driven by cranial allometric rules. Overall, colobins display proportionately larger parietal lobes and flat vaults, baboons show larger parietal lobes and taller vaults, cercopithecins exhibit larger occipital lobes and intermediate heights, and macaques tend to have average cercopithecid proportions. The deformation-based methods additionally reveal changes in the lateral dimensions, with baboons exhibiting mediolateral parietal expansion.
In sum, this study was successful in reproducing, through quantitative methods, previously described differences between cercopithecines and colobines. This was the first study attempting to separate the parietal lobe surface from the endocast, and the results suggest that our approach to extract the parietal region can be useful to study parietal lobe variation in extant and extinct species. In addition, our results evidence that, among papionins, baboons tend to display enlarged parietal proportions, like colobines. Given the differences in locomotor and feeding behavior between these taxa, similar lobe proportions are probably independent evolutionary traits. Interestingly, large parietal lobe proportions are displayed by seemingly less dexterous taxa. It would be interesting to also include highly dexterous taxa, such as Cebus, and assess the differences in somatosensory representations among cercopithecids to evaluate possible associations between the parieto-occipital cortical proportions and behavior.
Bones are the main source of information in bioarchaeology and paleoanthropology. They generally provide evidence on cranial anatomy but, in some cases, can also supply cues on soft tissues, including vessels. The internal cerebral vascular system does not leave any marks on the skull, but other networks do. In particular, the middle meningeal artery, the venous sinuses, and the emissary veins can be traced on the bone surface by means of their imprints and foramina. The human craniovascular network has been in the center of our team’s interest for a while now, also thanks to a grant supported from the Wenner Gren Foundation. After early surveys on this topic, recently we have published analyses of the diploic channels and of the parietal vessels, including on fossils, together with reviews on craniovascular traits and craniovascular evolution. Now, we have published a new study on the variability of craniovascular traits in normal adult populations. This paper investigates prevalence and associations between vascular characters, and provides a comparative frame for further studies. We studied two European samples of dry skulls with distinct cranial proportions (Czech and Italian), and provided a description of the variation and distribution of the main craniovascular features, as well as their correlation with cranial metrics. The traces of the middle meningeal vessels and venous sinuses seem to be independent on the cranial size and form. In case of foramina, only the number and size of mastoid foramina seem to be related to the cranial form and size (the bigger and wider the skull, the more the size and number of mastoid passages). Males have a higher prevalence of occipito-marginal sinus drainage, when compared with females. The cranial form of the Czech skulls tends to be brachycephalic, whereas the Italian skulls have more mesocephalic dimensions. These two populations display different anterior-posterior dominance of the middle meningeal branches, and different pattern of confluence of the sinuses (right vs. left dominance of transverse sinuses). Because these traits are not patently associated with cranial form, we can hypothesize that genetic factors, climate, or migrations can influence cranial proportions and craniovascular morphology independently.
Jager et al. recently investigated the identification and variability of cerebral sulcal imprints observed in 20 modern human endocasts through an observer-independent, automatic method. The most frequently identified sulci included the Sylvian fissure, as well as frontal and temporal sulci, while imprints on the parietal region were hardly identified. They observed hemispheric asymmetry and differences between sexes in the frequency of some sulcal imprints. On the other hand, there were no sex differences in sulcal patters. In general, these results are in agreement with previous analyses of sulcal patterns in brains. The authors intend to further extend this study by building a statistical model to document modern human variation in sulcal patterns and subsequently creating an automatic method for recognition of imprints in fossil hominin endocasts for use in paleoneurology.
Today we launch a new research line in our lab: Anatomical Network Analysis. Networks are employed in almost any field, to investigate patterns and levels of organization within different kinds of systems. In neuroanatomy, networks are frequently used to analyze connections. Anatomical Network Analysis, instead, applies network thinking and methods to macroscopic anatomy, to investigate the topological properties of organs and tissues. After a first exploratory survey on the Brodmann maps, we have now published a first research article on this topic, integrating issues in evolutionary neuroanatomy, paleoneurology, and functional craniology. Here the paper, and here a post.
The prefrontal cortex is the most anterior region in the frontal lobe of the brain and, in humans, it is associated with higher-order tasks involving complex cognition and behaviour. Throughout primate evolution there has been a trend for increasing brain size in which modern humans are the most extreme living example. Among all mammals, absolute brain size consistently increases with body mass, but many primates seem to have relatively larger brains than expected. In modern humans, our complex cognitive abilities have been long been associated with bigger brain size but some regions of the brain are suspected of being disproportionately larger than expected for our body size. Precisely which regions of the brain are disproportionately larger in modern humans compared to other primates remains unresolved and highly contentious. The prefrontal cortex is one of the regions suspected of being relatively larger in our species, although no consensus has been reached on this issue, most of all when fossils are included in the debate.
In 2018, Donahue and colleagues used Magnetic Resonance Imaging (MRI) to investigate relative prefrontal cortex size in modern humans, chimpanzees and macaques. The prefrontal cortex was defined using two different approaches from previous studies where opposing conclusions were found. Macromorphology defined the prefrontal cortex as all regions anterior to the genu of the corpus callosum, while cytoarchitecture used neuron densities, specifically, granular (high-density neurons) and dysgranular (modest-density neurons) to define the prefrontal cortex. Limitations of only including three species meant statistical regressions were unsubstantiated and allometry could not be investigated. However, relative prefrontal cortex size was examined by comparing the prefrontal cortex to total brain size and the size of the primary visual and primary motor cortices. Investigation of the prefrontal cortex was further subdivided into gray and white matter volumes. Results indicated modern humans had a larger prefrontal cortex, absolutely and relatively, compared to macaques and chimpanzees, with a specific increase in the proportion of white matter. Results comparing the two approaches of delineating the prefrontal cortex indicated that macromorphology consistently underestimated prefrontal cortex size in all species compared to cytoarchitectural definitions. It was concluded that modern humans possessed a disproportionately large prefrontal cortex, mostly argued on results from allometric regressions which were limited to three species. A reply questioned the conclusion that modern humans have a disproportionately enlarged prefrontal cortex on the basis of allometric regressions which were statistically unsound. Concerns were raised over the anthropocentric focus of these conclusions, instead arguing there was no evidence to refute a generalized scaling rule applicable to all primates when only three species were studied and regressions were inappropriate to indicate humans deviate from chimpanzees and macaques.
The most substantial findings seemed under-emphasised with findings of previous studies confirmed and macromorphology consistently underestimating prefrontal cortex size. Future research to better define the prefrontal cortex in primates is important as is the inclusion of more primate species to determine whether modern humans do have disproportionately enlarged prefrontal cortices compared to other primate species.
Hematopoiesis is the process by which blood cellular components are formed, and takes place especially within the bone marrow. The haematopoietic cells produce all types of blood cells and tissues including red blood cells (erythrocytes), lymphocytes (T-cells, B-cells and natural killer cells), and the myeloid types of cells (granulocytes, megakaryocytes, macrophages). The haematopoietic cells are self-renewing and in adults are present in the vertebrae, pelvis, ribs, sternum, skull, proximal end of long bones and scapulae, being the main components of the red marrow. The red marrow is gradually changing with age into yellow marrow (tissue rich in adipose cells) following a specific pattern, when the process starts at the distal phalanges and continues towards the axial skeleton. However, in some cases, yellow marrow can also be converted again into a hematopoietically active tissue. The skeleton plays a crucial role in the normal hematopoiesis and both systems (bone and blood) interact and influence each other. In their recent paper Valderrábano and Wu (2019) reviewed the effect of various diseases of the circulatory system on the skeleton. The authors mention chronic disorders of hematopoiesis (thalassemia and sickle cell anemia) which are connected to the bone loss and increased fracture risk. Then they further discuss anemia and its association with the bone fragility in older adults. In anemia, the hemoglobin in the blood decreases (by decreasing the number of healthy red blood cells) which results in lower ability of the blood to carry oxygen. Anemia is most commonly caused by a nutritional deficiency (frequently the iron deficiency) or by the inflammation of chronic disease. Bone fragility and fracture risk are usually estimated based on the bone mineral density (BMD) test. Several authors have studied the association of BMD and amount of hemoglobin in the blood but with different results and methodology. The mechanisms behind the bone fragility in anemia and other circulatory diseases are unclear. The role of increased erythropoiesis (producing red blood cells) and its demands on the bone tissue was considered as a possible factor of impairment of bone cells. Possibly, a change in the mechanical and loading properties of bone marrow due to anemia could be also affecting the strenght of the bone. Nevertheless, more studies are needed to fully understand the interactions between the bone tissue and hematopoietic cells, and to discuss potential clinical implications.
The sound quality of string instruments depends on many factors, including the thickness of the wood that forms the resonance box. Because of the complicated (and delicate) architecture of a musical instrument, measuring that thickness can be tricky. The Hacklinger caliper is a device able to measure a distance by virtue of a magnetic field, and it is used by luthiers to check the thickness of violins and guitars. Definitely useful to musicians and, of course, to anthropologists too. Computed tomography is wonderful to measure cranial thickness, but it is expensive, time-consuming, and not always easy to employ in many museum collections. The Hacklinger caliper is cheap and portable. Irene del Olmo has coordinated this study in which we use the Hacklinger caliper to measure the distribution of cranial thickness in archaeological samples. Conclusion: it works!