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!
Platyrrhines (or New World Monkeys – NWM) inhabit South America and there are currently 5 families and 151 species, possessing traits not found in Catarrhines (Apes and Old World Monkeys of Africa and Asia). The NWM fossil record is fragmentary, with the earliest fossil specimens found in Argentina and dated to the middle Miocene (~ 22 million years ago), and more recent fossil remains found on the Caribbean islands and dated to the Late Pleistocene or early Holocene (~ 20-5 thousand years ago). The evolutionary relationships among living NWM and fossil species remain highly speculative. However, Woods et al. (2018) reported the successful recovery of ancient DNA from a Jamaican fossil species Xenothrix, closely related to living species of the Callicebinae, the Titi monkeys. The continuing uncertainty surrounding NWM evolutionary history has resulted in several Caribbean fossil NWM assigned as tentative ancestral species to living howler monkeys (genus Alouatta) based on similarities of highly prognathic faces, robust crania and smaller than expected brain size or endocranial volume (ECV).
A recent study by Halenar-Price & Tallman (2019) examined cranial shape and potential correlation with ECV in three Caribbean fossil and four living NWM genera. Patterns of cranial shape were determined for each living NWM species using geometric morphometrics and, once controlling for absolute size and phylogeny, the correlation with ECV was investigated using an encephalization quotient (EQ). Results from statistical tests for a correlation between cranial shape and brain size indicated no strong support for common trend for cranial shape describing the entire NWM clade, with the overall effect of cranial shape change in living NWM only slightly associated with brain size or ECV (less than 10%). Instead, cranial shape change was very species-specific, with species often differing in cranial width, cranial base flexion and globularity of the cranial vault. The howler monkeys had the lowest association between ECV and cranial shape, while the saki monkeys (genus Pithecia), showed greater links between ECV and cranial shape change associated with seed-eating diet and presence of cranial crests.
To examine fossil NWM and the role of encephalization on cranial shape, phylogeny was accommodated and fossil NWM added to the analyzes. Results indicated that Dominican Republic fossil NWM Antillothrix had a higher encephalization quotient (EQ) than living howler monkeys and was instead within range of titi monkeys (genus Callicebus), while Brazilian fossil NWM Cartelles was within the range of living howler monkeys. However, the Cuban fossil NWM Paralouatta was below the range of living howler monkeys. This study highlighted that the combined presence of facial prognathism, robust cranial form and smaller than expected brain size in NWM was strongly influenced by species-specific patterns related to diet, physiological and ecological adaptations, where, in very generalized terms, similarities between fossil and living new world monkeys do not necessarily indicate shared evolutionary associations.
Here a recent study on the cranial morphology of howler monkeys, and an article on atelids and ethnozoology.
Attendants from the Royal College of Surgeons packing up human skulls to send to the Natural History Museum in London, England, on the 1st of July, 1948.
[from The Olduvai Gorge]
Cranial foramina are small openings of the cranial bones that allow the passage of nerves and blood vessels. During ontogeny, they develop in specific locations and usually remain open throughout the whole life of an individual. Recently McGonnell and Akbareian (2018) published a review on what is currently known about these anatomical elements. The authors observed the development of the foramina in chick embryos. They discuss the possible influence of different origins of the bone tissue (mesoderm or neural crest) and type of ossification (endochondral or intramembranous) in the formation and maintenance of the foramina. They also discuss the role of nerves and blood vessels in the formation of “zones of inhibition” which probably direct the foramen development. The authors also considered the impact of some diseases and syndromes on malformation or closing of the foramina. Specifically, they mention craniosynostosis, achondroplasia, hyperostosis, sclerosis, Chiari malformation, and osteopetrosis as conditions which may lead to significant alteration of their functions. Malformation can negatively affect the functions of major nerves or blood vessels, and even cause blindness, deafness and high intracranial pressure which can be fatal. In anthropology, cranial foramina together with other intracranial traits are considered in research of biological distances, population studies, paleoanthropology, paleopathology and forensic sciences (Píšová et al. 2017). Size and location of cranial foramina are used as proxies for their respective nerves and blood vessels. However, McGonnell and Akbareian also question the reliability and validity of this approach in case of fossil samples, considering our limited knowledge on the foramina development, and the fact that they might contain more than just one element (nerve or vessel). More comprehensive studies exploring human cranial foramina and their association with vascular and neural structures are needed, as well as better understanding of their interaction within the cephalic system.
The brain is a soft-tissue organ surrounded by the bony structure of the skull, where changes in one require changes in the other. From infancy, the bones of the skull are separated by membranous sutures and with rapid brain expansion, these membranous regions of the skull are replaced by bone, fusing the skull into a protective structure around the adult brain. Ontogeny describes changes in the same anatomical structure throughout the life cycle, including the differences between age groups, within a species and across species, while allometry can explain size-related changes to skull shape, particularly between species. The individual bones of the skull join at sutures to form modules which include the facial block, the cranial vault and the cranial base.
A new paper by Scott et al. (2018) examined allometry and ontogeny in the hominid skull. The skulls from three hominid (great ape) species included the Bornean orangutan, the Western lowland gorilla and the common chimpanzee from several age groups were analyzed, and geometric morphometrics was used to capture shape change and allometry in the facial block and endocranium (as an indirect proxy for brain form). Covariation between the facial block and endocranium was tested using 2-block partial least-squares analysis. Results for ontogeny suggested endocranial change was lesser in younger age groups but with increasing age, orangutans separated from gorillas and chimpanzees, showing the greatest difference in face-to-brain shape. Results for allometry indicated that changes in facial shape were mostly related to size differences. However, the endocranium was not entirely influenced by changes in size, suggesting shape change in the endocranium is somewhat independent.
Ultimately, Scott and colleagues have shown the covariation between the facial block and the endocranium was more conserved in all three ape species in younger age groups, but the facial block continued to change shape into adulthood even after the brain growth had stopped. This suggests the endocranium is driven by changes to brain form during earlier stages of life before the cranial vault exerts a greater influence in late adolescence. However, the greatest change to skull morphology occurred during adulthood in facial shape.
A recent work, analyzing the development and evolution of the primate cortical folding, evidences two separate folding processes of the neocortex. Namba and colleagues examine two subtypes of neocortex, the dorsal isocortex, defined as the portion of neocortex limited laterally by the lateral fissure (LF) and medially by the cingulate sulcus (CiS), and the proisocortex within these same boundaries, comprising the insular cortex and the cingulate cortex, respectively. Their sample was composed by three to five specimens from 13 different primate species, including two great apes (humans and chimpanzees), two Old World monkeys, four New World monkeys, one tarsier, one galago, and three lemurs. For each specimen they analyzed five comparable coronal sections. They measured the gyrencephalic index (GI) as the ratio of the length of the inner to outer cortex contours, and calculated the LF score as the ratio of the LF greatest depth to the maximum width of the hemisphere. Then they analyze the relationships between LF score, and the GI values for the dorsal isocortex, the cingulate and insular cortices, and the neocortex, which included the three cortices and the temporal isocortex. To provide an evolutionary perspective, they reconstruct GI and LF score values for the primate ancestors. Furthermore, they examine the timing of folding in a longitudinal sample of humans and long-tailed macaques, and the folding differences in human lissencephalic patients, for a developmental and genetic overview. The proisocortex showed a similar GI across the sample, and the reconstructed ancestor LF scores were in the same magnitude as those of the 13 present-day primates. Conversely, the degree of folding of the dorsal isocortex differs across the species, and between the ancestors and the extant species, increasing with increasing folding of the neocortex. Furthermore, their analyses also revealed that LF and CiS appear earlier in development, while the dorsal isocortex starts to fold later. This portion of the cortex is also the most affected in human lissencephaly, as the LF, and CiS to a lesser degree, are still detectable in all grades of malformation. Hence, the authors conceptualize the folding of the neocortex as two distinct and sequential processes. The conserved folding occurs earlier in development, at the boundaries between the proisocortex and the dorsal isocortex, and involves the formation of the LF and CiS. The evolved folding occurs within the isocortex, after the onset of the conserved folding. Moreover, the authors suggest these two processes might be influenced by different cellular mechanisms, with neuron production contributing more to the conserved folding, and neuron migration to the evolved folding, a matter deserving further investigation.
In evolutionary biology, microevolution and macroevolution impact on the variation and covariation between genotype and phenotype. A related concept is the biological ability of an organism to adapt and evolve, or its evolvability, which is of keen interest to evolutionary biologists. The quantification of genetic change is analysed via the genetic variance-covariance matrix (G-matrix) while phenotypic change is analysed via the phenotypic variance-covariance (P-Matrix). Under the assumption of a neutral evolutionary model with the absence of genetic drift, the G-matrix should be proportional to a P-matrix. Although there is potential for theoretical complications arising from organisms with higher evolvability biasing the rates of evolutionary change, this is not fully investigated and seems to warrant further empirical studies.
The diversity of craniofacial form observed in fossil species of genus Homo and modern humans has been examined in terms of craniofacial adaptation to various biomechanical and environmental stressors. The absence of recovered genomes from species of fossil Homo beyond Homo neanderthalensis and fossil Homo sapiens has required studies of fossil human phylogenetics to rely on high uncertainties in the estimation of fossil hominin phylogeny and further restricted by small sample sizes.
In a recent study, Baab (2018) used the rate of evolutionary change in populations of modern Homo sapiens to estimate evolutionary rates in species of fossil Homo, analyzing craniofacial shape change, diversification and evolvability in the genus Homo. Results were consistent with independent conclusions that a neutral evolutionary model was adequate to generate the diversity in craniofacial form observed in the genus Homo. Once accounting for the small fossil sample size and the degree of evolutionary rate being higher than chance, there was no statistically significant support for higher rates of evolvability generating more rapid rates of evolutionary change across the entire genus Homo.
In contrast, the more recent lineages showed some evidence for selection acting at a greater magnitude in H. neanderthalensis and early H. sapiens, generating a more rapid rate of evolutionary change. Baab (2018) suggests brain expansion may be a likely contributor influencing the more rapid evolutionary rate change in craniofacial shape as observed in early H. sapiens and H. neanderthalensis and why only the more recent lineages of the genus Homo were affected by such rapid changes in craniofacial form.