Modern human origins

Human Evolution: The Real Cause for Birth Palsy

OBJECTIVE

Birth palsy, otherwise known as obstetric brachial plexus paralysis (OBPP), is a closed stretch injury to the brachial plexus of nerves during the birth process resulting in varying degree of paralysis and contractures of the upper limb. The study aimed to find out the susceptibility of humans and small-bodied primates to birth palsy.

METHOD

A comparative study on parturition in modern humans, hominoids, hominids, small-bodied primates and great apes was done to determine if the changes in female pelvis and neonatal head and shoulder during human evolution is the real cause for OBPP.

RESULTS

During evolution, the morphology of the female pelvis and birth canal changed into a narrow and twisted one and also the size of the fetal head increased. Thus, the narrow and twisted pelvis of the mother, and the relatively large head and broad shoulders of the newborn has made the birthing process of modern human and small bodied primates a precarious fine-tuned act with a very narrow margin for error. This has necessitated proper obstetric care to reduce or even at times obviate the incidence of birth injuries like OBPP.

CONCLUSION

Human evolution has made human babies susceptible to birth palsy and thus is the real cause of birth palsy.

Genomic evidence for an African expansion of anatomically modern humans by a Southern route

There is general agreement among scientists about a recent (less than 200,000 yrs ago) African origin of anatomically modern humans, whereas there is still uncertainty about whether, and to what extent, they admixed with archaic populations, which thus may have contributed to the modern populations' gene pools. Data on cranial morphology have been interpreted as suggesting that, before the main expansion from Africa through the Near East, anatomically modern humans may also have taken a Southern route from the Horn of Africa through the Arabian peninsula to India, Melanesia and Australia, about 100,000 yrs ago. This view was recently supported by archaeological findings demonstrating human presence in Eastern Arabia >90,000 yrs ago. In this study we analyzed genetic variation at 111,197 nuclear SNPs in nine populations (Kurumba, Chenchu, Kamsali, Madiga, Mala, Irula, Dalit, Chinese, Japanese), chosen because their genealogical relationships are expected to differ under the alternative models of expansion (single vs. multiple dispersals). We calculated correlations between genomic distances, and geographic distances estimated under the alternative assumptions of a single dispersal, or multiple dispersals, and found a significantly stronger association for the multiple dispersal model. If confirmed, this result would cast doubts on the possibility that some non-African populations (i.e., those whose ancestors expanded through the Southern route) may have had any contacts with Neandertals.

On the trails of markers and proxies: the socio-cognitive technologies of human movement, knowledge assemblage, and their relevance to the etiology of nasopharyngeal carcinoma

Bacteria, pigs, rats, pots, plants, words, bones, stones, earrings, diseases, and genetic indicators of all varieties are markers and proxies for the complexity of interweaving trails and stories integral to understanding human movement and knowledge assemblage in Southeast Asia and around the world. Understanding human movement and knowledge assemblage is central to comprehending the genetic basis of disease, especially of a cancer like nasopharyngeal carcinoma. The problem is that the markers and trails, taken in isolation, do not all tell the same story. Human movement and knowledge assemblage are in constant interaction in an adaptive process of co-production with genes, terrain, climate, sea level changes, kinship relations, diet, materials, food and transport technologies, social and cognitive technologies, and knowledge strategies and transmission. Nasopharyngeal carcinoma is the outcome of an adaptive process involving physical, social, and genetic components.

GENETICS AND RECENT HUMAN EVOLUTION

Starting with "mitochondrial Eve" in 1987, genetics has played an increasingly important role in studies of the last two million years of human evolution. It initially appeared that genetic data resolved the basic models of recent human evolution in favor of the "out-of-Africa replacement" hypothesis in which anatomically modern humans evolved in Africa about 150,000 years ago, started to spread throughout the world about 100,000 years ago, and subsequently drove to complete genetic extinction (replacement) all other human populations in Eurasia. Unfortunately, many of the genetic studies on recent human evolution have suffered from scientific flaws, including misrepresenting the models of recent human evolution, focusing upon hypothesis compatibility rather than hypothesis testing, committing the ecological fallacy, and failing to consider a broader array of alternative hypotheses. Once these flaws are corrected, there is actually little genetic support for the out-of-Africa replacement hypothesis. Indeed, when genetic data are used in a hypothesis-testing framework, the out-of-Africa replacement hypothesis is strongly rejected. The model of recent human evolution that emerges from a statistical hypothesis-testing framework does not correspond to any of the traditional models of human evolution, but it is compatible with fossil and archaeological data. These studies also reveal that any one gene or DNA region captures only a small part of human evolutionary history, so multilocus studies are essential. As more and more loci became available, genetics will undoubtedly offer additional insights and resolutions of human evolution.

Human migrations and population structure: what we know and why it matters

The increasingly obvious medical relevance of human genetic variation is fueling the development of a rich interface between medical genetics and the study of human genetic history. A key feature of this interface is a step increase in the size and diversity of genetic data sets, permitting a range of new questions to be addressed concerning our evolutionary history. Similarly, methodologies first developed to study genetic history are being tailored to address medical challenges, including mapping genes that influence diseases and variable drug reactions. In this paper we do not attempt a comprehensive review of human genetic history. Rather we briefly outline some of the complications and challenges in the study of human genetic history, drawing particular attention to new opportunities created by the explosive growth in genetic information and technologies. First we discuss the complexity of human migration and demographic history, taking both a genetic and archaeological perspective. Then we show how these apparently academic issues are becoming increasingly important in medical genetics, focusing on association studies, the common disease/common variant hypothesis, the evaluation of variable drug response, and inferences about gene function from patterns of genetic variation. Finally we describe some of the inferential approaches available for interpreting human genetic variation, focusing both on current limitations and future developments.

Middle Palaeolithic burial is not a dead issue: the view from Qafzeh, Saint-Césaire, Kebara, Amud, and Dederiyeh

Inferences of purposeful Middle Palaeolithic (MP) burial are almost universally accepted, despite published arguments that the pre-1960s discoveries are equally well explained by natural processes. In the modern human origins debate (perhaps the most hotly disputed question in palaeoanthropology) inferences of MP burial are crucial in arguments for an early Upper Pleistocene emergence of modern humans. The present paper contributed to that debate by re-examining a number of post-1960s excavations of MP hominid remains. Because these were excavated with meticulous attention to depositional circumstances and stratigraphic context, most palaeoanthropologists consider these inferences of purposeful burial to be based on irrefutable evidence. This paper focuses on the reasoning behind such claims, especially the assumption that articulated sketetal material is prima facie evidence for deliberate burial. First it reviews a range of processes operating in caves and rockshelters that condition the probability of articulated skeletal material preserving without hominid intervention. Processes such as deposition, decomposition, and disturbance are inherently more variable in caves and rockshelters than is usually acknowledged. The first section concludes that purposeful protection is not necessary to account for the preservation of articulated skeletal remains. The second part of the paper examines the published record from Qafzeh, Saint-Césaire, Kebara, Amud and Dederiyeh, where the majority of the remains claimed to have been buried are fragmented, incomplete, and disarticulated. This re-examination suggests that in all of the post-1960s cases of putative burial, the hominid remains occur in special depositional circumstances, which by themselves are sufficient to account for the preservation in evidence at these sites. This conclusion severely weakens arguments for purposeful burial at the five sites. Moreover, the equivocal nature of the evidence in the more recent cases renders even less secure the similar claims made for discoveries of hominid skeletal remains at La Chapelle-aux-Saints, Le Mousterier, La Ferrassie, Teshik-Tash, La Grotte du Régourdou, Shanidar, and several others. Finally, by highlighting the equivocal nature of the evidence, this paper underscores the ongoing need for palaeoanthropologists to specify as wide a range of taphonomic processes as possible when interpreting the archaeological record. This will aid in producing robust inferences, and will bring about increasingly accurate knowledge of when hominids became human.

Genetic admixture in the late pleistocene

The replacement hypothesis of modern human origins holds that the original population of modern humans expanded throughout the world, replacing existing archaic populations as it went. If this expanding population interbred with the peoples it replaced, then some archaic mitochondria might have been introduced into the early modern gene pool. Such mitochondria would be recognizable today because they should differ from other modern mitochondria at several times the number of sites that we are used to seeing in pairwise comparisons. In this paper we ask what can be inferred from the absence of these "divergent" mitochondria from modern samples. We show that if the effective number of females in our species has been large for the past 40,000 years, then the level of admixture must have been low. For example, if this effective number exceeded 1.6 million, then we can reject the hypothesis that more more than 2/1,000 of the mitochondria in the early modern population derived from admixture with archaic peoples. We argue elsewhere that regional continuity would be detectable in the fossil record only if the rate of admixture exceeded 76%. Here, we show that this level of admixture would require the effective female size of the human population to have been less than 1,777 for the past 40,000 years.

Comparison of craniofacial features of major human groups

Distance analysis and factor analysis, based on Q-mode correlation coefficients, were applied to 23 craniofacial measurements in 1,802 recent and prehistoric crania from major geographical areas of the Old World. The major findings are as follows: 1) Australians show closer similarities to African populations than to Melanesians. 2) Recent Europeans align with East Asians, and early West Asians resemble Africans. 3) The Asian population complex with regional difference between northern and southern members is manifest. 4) Clinal variations of craniofacial features can be detected in the Afro-European region on the one hand, and Australasian and East Asian region on the other hand. 5) The craniofacial variations of major geographical groups are not necessarily consistent with their geographical distribution pattern. This may be a sign that the evolutionary divergence in craniofacial shape among recent populations of different geographical areas is of a highly limited degree. Taking all of these into account, a single origin for anatomically modern humans is the most parsimonious interpretation of the craniofacial variations presented in this study.

The myth of Eve: molecular biology and human origins

It has been proposed that modern humans descended from a single woman, the "mitochondrial Eve" who lived in Africa 100,000 to 200,000 years ago. The human immune system DRB1 genes are extremely polymorphic, with gene lineages that coalesce into an ancestor who lived around 60 million years ago, a time before the divergence of the apes from the Old World monkeys. The theory of gene coalescence suggests that, throughout the last 60 million years, human ancestral populations had an effective size of 100,000 individuals or greater. Molecular evolution data favor the African origin of modern humans, but the weight of the evidence is against a population bottleneck before their emergence. The mitochondrial Eve hypothesis emanates from a confusion between gene genealogies and individual genealogies.

Molecular genetics of speciation and human origins

The major histocompatibility complex (MHC) plays a cardinal role in the defense of vertebrates against parasites and other pathogens. In some genes there are extensive and ancient polymorphisms that have passed from ancestral to descendant species and are shared among contemporary species. The polymorphism at the DRB1 locus, represented by 58 known alleles in humans, has existed for at least 30 million years and is shared by humans, apes, and other primates. The coalescence theory of populations genetics leads to the conclusion that the DRB1 polymorphism requires that the population ancestral to modern humans has maintained a mean effective size of 100,000 individuals over the 30-million-year persistence of this polymorphism. We explore the possibility of occasional population bottlenecks and conclude that the ancestral population could not have at any time consisted of fewer than several thousand individuals. The MHC polymorphisms exclude the theory claiming, on the basis of mitochondrial DNA polymorphisms, that a constriction down to one or few women occurred in Africa, at the transition from archaic to anatomically modern humans, some 200,000 years ago. The data are consistent with, but do not provide specific support for, the claim that human populations throughout the World were at that time replaced by populations migrating from Africa. The MHC and other molecular polymorphisms are consistent with a "multiregional" theory of Pleistocene human evolution that proposes regional continuity of human populations since the time of migrations of Homo erectus to the present, with distinctive regional selective pressures and occasional migrations between populations.

Matrix correlation tests support a single origin for modern humans

The debate over human origins has focused on two competing theories. The single African origin model holds that anatomically modern Homo sapiens evolved in Africa 100,000-200,000 years ago. Members of this population migrated out of Africa, replacing archaic human groups through Asia and Europe, with racial differentiation occurring within the past 100,000 years. The alternative regional continuity model proposes continuous evolution over the past million years, with racial variation developing early, and similar modern human traits developing in all regions as the result of worldwide gene flow. The persistence of specific morphological features within regions over the past million years supports regional continuity, whereas the identification of anatomically modern fossil specimens from Africa and the Levant 50-60,000 years before they are found elsewhere, provides support for a single origin. I give here the first quantitative test of the fossil evidence for each of these models. Results support a single African and/or Levantine origin for modern humans.

Is the Narmada hominid an Indian Homo erectus?

In 1982 a fossil hominid calvaria was found in a middle Pleistocene deposit in the central Narmada valley of Madhya Pradesh, India, and was assigned to the new taxon Homo erectus narmadensis. Subsequently, morphometric studies of the specimen were conducted by two separate research teams from France and the United States, both in collaboration with Indian colleagues. Results of the most recent study, which includes morphometric and comparative investigations, lead to the conclusion that "Narmada Man" is appropriately identified as Homo sapiens. While the calvaria shares some anatomical features with Asian Homo erectus specimens, it exhibits a broader suite of morphological and mensural characteristics suggesting affinities with early Homo sapiens fossils from Asia, Europe, and Africa as well as demonstrating that the Narmada calvaria possesses some unique anatomical features, perhaps because the specimen reflects the incoherent classificatory condition of the genus Homo.