Human Evolution

[Jo Bowyer]

Why human evolution should be a basic science for medicine and psychology students.

http://www.ncbi.nlm.nih.gov/pubmed/2...?dopt=Abstract

Based on our teaching experience in medicine and psychology degree programs, we examine different aspects of human evolution that can help students to understand how the human body and mind work and why they are vulnerable to certain diseases. Three main issues are discussed: 1) the necessity to consider not only the mechanisms, i.e. the "proximate causations", implicated in biological processes but also why these mechanisms have evolved, i.e. the "ultimate causations" or "adaptive significance", to understand the functioning and malfunctioning of human body and mind; 2) examples of how human vulnerabilities to disease are caused by phylogenetic constraints, evolutionary tradeoffs reflecting the combined actions of natural and sexual selection, and/or mismatch between past and present environment (i.e., evolution of the eye, teeth and diets, erect posture and their consequences); 3) human pair-bonding and parent-offspring relationships as the result of socio-sexual selection and evolutionary compromises between cooperation and conflict. These psychobiological mechanisms are interwoven with our brain developmental plasticity and the effects of culture in shaping our behavior and mind, and allow a better understanding of functional (normal) and dysfunctional (pathological) behaviors. Thus, because the study of human evolution offers a powerful framework for clinical practice and research, the curriculum studiorum of medical and psychology students should include evolutionary biology and human phylogeny.

via neuroskeptic's twitter feed




A recently published Cornell University study describes how shifts in the diets of Europeans after the introduction of farming 10,000 years ago led to genetic adaptations that favored the dietary trends of the time.

https://www.sciencedaily.com/release...0612153554.htm

Before the Neolithic revolution that began around 10,000 years ago, European populations were hunter-gatherers that ate animal-based diets and some seafood. But after the advent of farming in southern Europe around 8,000 years ago, European farmers switched to primarily plant-heavy diets.

The study -- the first to separate and compare adaptations that occurred before and after the Neolithic Revolution -- reveals that these dietary practices are reflected in the genes of Europeans.

"The study shows what a striking role diet has played in the evolution of human populations," said Alon Keinan, associate professor of computational and population genomics and the paper's senior author. Kaixiong Ye, a postdoctoral researcher in Keinan's lab, is the paper's lead author.

The study has implications for the growing field of nutritional genomics, called nutrigenomics. Based on one's ancestry, clinicians may one day tailor each person's diet to her or his genome to improve health and prevent disease.

The study shows that vegetarian diets of European farmers led to an increased frequency of an allele that encodes cells to produce enzymes that helped farmers metabolize plants. Frequency increased as a result of natural selection, where vegetarian farmers with this allele had health advantages that allowed them to have more children, passing down this genetic variant to their offspring.

Update 13/06/2017

[Jo Bowyer]

Fossil skulls reveal that blood flow rate to the brain increased faster than brain volume during human evolution

http://rsos.royalsocietypublishing.o...ent/3/8/160305

Introduction

The most distinctive feature of modern Homo sapiens is the relatively large size of the brain and its high metabolic rate. Across evolutionary history, the hominin brain has undergone increases in size [1,2] and reorganization associated with cognitive specialization [3,4]. To explain the drivers for hominin brain evolution, an emphasis has been placed on understanding hominin cerebral metabolic evolution. The human body allocates 20–25% of total resting metabolic rate to brain function, compared with 8–10% for non-human primates and 3–5% for most non-primate mammals [5–7]. Hominin cerebral metabolic evolution has been proposed to relate to changes in neuronal function and the establishment of specialized communication and metabolic energy pathways [8].

The brain is an entirely aerobic organ that does not store glucose or much glycogen, and so relies on a constant blood supply. Glucose is the prime metabolic fuel and a substrate for biosynthesis [9,10], while oxygen is necessary for oxidative phosphorylation that produces ATP for neuronal and synaptic functions. Although energy is used for diverse cellular activities in the brain, and metabolic rates can shift dramatically between regions of the cerebrum in the short term [11], the overall blood flow rate (perfusion) and metabolic rate of the cerebrum changes little between rest, high cognitive activity, physical exercise and sleep [12–14]. Furthermore, in vivo rates of cerebral blood flow, oxygen consumption and glucose uptake scale almost identically with brain volume among mammals, with interspecific exponents of the allometric power equation ranging between 0.82 and 0.87 [9,15–17]. The exponents are lower than direct proportionality (1.0), but greater than the three-quarter exponent (0.75) predicted by the empirical relationship between resting metabolic rate and whole body mass of mammals, known as ‘Kleiber's Law’ [18]. In the primate order, however, neuron numbers increase linearly with brain mass while the volume of individual neurons remains constant [19]. These findings imply that the human brain could be, at a neurological and metabolic level, simply a linearly scaled-up version of the primate brain [20]. Indeed, our estimate of cerebral blood flow rate in 34 species of haplorrhine primates, scales with brain volume to the 0.95 power, which is not significantly different from 1.0 [21]. However, the scaling of brain perfusion in living mammals or primates might not represent the evolution of brain perfusion in hominins.

We use the lumen radius of the internal carotid arteries (ICAs) to deduce changes in cerebral brain metabolism throughout hominin evolution, with the understanding that metabolic rate, blood flow rate and arterial size are tightly related. In haplorrhine primates, including hominins, the perfusion of blood to the cerebrum, the specialized region of the brain responsible for cognitive function, is almost exclusively derived from two ICAs that pass through the carotid canals in the petrous parts of the temporal bones [22,23]. In humans, the ICAs give rise to the middle cerebral arteries that service the lateral parts of the frontal, parietal and temporal lobes, and the anterior cerebral arteries that service the medial parts of the frontal and parietal lobes. The paired vertebral arteries join to form the basilar artery that services the occipital lobes, cerebellum and brain stem. According to data for the radii of these arteries [24], the ICAs supply 85% of total brain blood flow and the basilar artery supplies 15%. These arteries potentially communicate via the Circle of Willis. However, flow through the posterior communicating arteries of the Circle in normal humans can occur in either direction and with velocities that are similar in individuals with bilateral or unilateral vessels [25], and the rate of flow is certainly less than 10% of total brain perfusion, based on their radii [24]. This information indicates that the ICAs are nearly the exclusive blood supply to the cerebrum, and the vertebral and basilar arteries normally play almost no role. Rarely, cerebral perfusion can occur through several collateral arteries if the ICAs are congenitally reduced or absent, and in such cases, the carotid canals in the skull are also reduced or absent [26,27].

The lumen size and wall thickness of large arteries are dynamically controlled throughout life by blood flow requirements and blood pressure [28]. The relationships are so well known as to be ‘laws’ [29]. Wall thickness approximately conforms to the Law of Laplace, in which thickness is proportional to radius and internal pressure [30], and arterial size conforms to Murray's Law that reduces the energy required for circulation [31]. For example, if blood flow rate in the rat common carotid artery is reduced by 35% experimentally, the inner radius of the artery decreases over several weeks to within 11% of the theoretical value derived from the shear stress equation (see Material and methods) that normalizes the frictional force of flowing blood acting on the endothelial lining of the arterial wall [32]. Because the ICAs are not accompanied by significantly sized veins or nerves [33], and they pass snugly through the carotid canal [34], it is possible to estimate blood flow rate from the radius of the carotid foramen in the skull. Using this technique, we estimate total cerebral blood flow rate via the left and right ICAs (Q˙ICAQ˙ICA; cm3 s−1), from the size of the internal carotid foramina of 35 fossil specimens from 12 hominin species. We use this as a proxy for cerebral metabolic rate and cognitive evolution, assuming that the fraction of oxygen extracted from the blood is size-independent, as it is in the whole body of resting mammals [35]. We then scale Q˙ICAQ˙ICA against body size, brain volume and fossil age to show the evolutionary progression of the hominin brain.

[marcel]

They say: " the overall blood flow rate (perfusion) and metabolic rate of the cerebrum changes little between rest, high cognitive activity, physical exercise and sleep"

These authors (below) found,.....

Cerebral blood flow during exercise: mechanisms of regulation.
Ogoh S, Ainslie PN.

Abstract

The response of cerebral vasculature to exercise is different from other peripheral vasculature; it has a small vascular bed and is strongly regulated by cerebral autoregulation and the partial pressure of arterial carbon dioxide (Pa(CO(2))). In contrast to other organs, the traditional thinking is that total cerebral blood flow (CBF) remains relatively constant and is largely unaffected by a variety of conditions, including those imposed during exercise. Recent research, however, indicates that cerebral neuronal activity and metabolism drive an increase in CBF during exercise. Increases in exercise intensity up to approximately 60% of maximal oxygen uptake produce elevations in CBF, after which CBF decreases toward baseline values because of lower Pa(CO(2)) via hyperventilation-induced cerebral vasoconstriction. This finding indicates that, during heavy exercise, CBF decreases despite the cerebral metabolic demand. In contrast, this reduced CBF during heavy exercise lowers cerebral oxygenation and therefore may act as an independent influence on central fatigue. In this review, we highlight methodological considerations relevant for the assessment of CBF and then summarize the integrative mechanisms underlying the regulation of CBF at rest and during exercise. In addition, we examine how CBF regulation during exercise is altered by exercise training, hypoxia, and aging and suggest avenues for future research.

https://www.somasimple.com/forums/sh...ad.php?t=25888

[Jo Bowyer]

What teeth reveal about the lives of modern humans

https://www.sciencedaily.com/release...0109191553.htm

When anthropologists of the future find our fossilized teeth, what will they be able to conclude about our lives?

Debbie Guatelli-Steinberg has an idea. She is a professor of anthropology at The Ohio State University who studies fossilized teeth to answer questions about the life history, growth, and diet of primates and our human ancestors, as well as the relationships between different species.

In a new book, What Teeth Reveal About Human Evolution (Cambridge University Press, 2016), she gives a broad overview of what scientists have learned about our ancestors from studying fossilized teeth.

As for the teeth of humans living today -- well, it is a good thing we have modern dentistry.

"We have teeth that were adapted for eating a very different diet than the one we eat today, at least in Western societies," Guatelli-Steinberg said.

In the book, she noted that 99 percent of humans' evolutionary history was spent eating foods that were hunted or gathered. Our current diets of soft, processed and sugary foods are nothing like the diets for which our teeth are adapted.

"Problems like cavities and plaque buildup have been magnified tremendously in humans today," she said. "Natural selection has not prepared us well for the kinds of food we eat today."

In addition to having much higher rates of cavities and plaque, modern humans are much more likely to have misaligned teeth that require orthodontic treatment or surgery.

"Soft diets do not stimulate jaw growth, and teeth, especially our third molars (wisdom teeth), become impacted," she said.

Fascinating!

Worth a read if you are a cranial osteopath and/or work with dental or orthodontic patients or those with chronic head pain.

[nykinvic]

Thanks for sharing Jo. Makes sense that it's not just what we eat but how we eat it that literally shapes us. I wonder if there is a movement equivalent? How does our modern sedentary/active sedentary mostly indoor lifestyle shape our bones and neuroimmune and cardiovascular systems?

[cathyph]

[QUOTEIn addition to having much higher rates of cavities and plaque, modern humans are much more likely to have misaligned teeth that require orthodontic treatment or surgery..[/QUOTE]

And that has generated a whole new approach to orthodontia, including interventions for airway management. I teach dentists the "Neurophysiology of Dental Interventions" so they can get more correction for less interference.

Also what I've seen over the past 18 years of teaching mouth work classes is that we seem to be de-volving our wisdom teeth. No need to keep gnarly chewing at age 15 after all your teeth have rotted out? No need for them any more. More and more students show up with either an incomplete set or none at all!

[Jo Bowyer]

Thanks for sharing Jo. Makes sense that it's not just what we eat but how we eat it that literally shapes us. I wonder if there is a movement equivalent? How does our modern sedentary/active sedentary mostly indoor lifestyle shape our bones and neuroimmune and cardiovascular systems?

I have seen some changes over the forty years I have been treating patients. The generation I started with were the babies born in the mid seventies at one end and Victorians at the other.

Obesity was rare, morbid obesity almost unknown. There was a massive problem with smoking related illness and what we would now consider to be avoidable accidents on the roads and in the workplace.

Going to the gym was comparatively rare as many more were involved in hard physical work.

We worked hard, there was lifting and manual handling instruction but we were all expected to be physically strong enough to work long hours and do a lot of lifting and manual handling.

Nowadays, I would not be allowed to run a stroke rehab group the way I did in the 80s. My hospital was understaffed and underfunded and I brought relatives in and trained them to work with their family members.

Pain and effort was an expected part of rehab and there was much less chronic and complex pain. Pain control was rudimentary and I did find this very difficult with post surgical and oncology patients.

Preventative health care has improved and patients are better educated, but I think that they sometimes find it more difficult to see cause and effect as it relates to them as individuals.

I remember seeing a documentary a few years ago which depicted two brothers, one a paediatrician and the other, an expedition doctor, who went to live with a tribe. They gained tremendous kudos for their medical skills but were kidded about their sadly lacking hunter gathering abilities. One said to the other, "We may be good doctors, but we're no good as men, we can't build rafts and climb trees and we can't get food". The tribal guys agreed, but they hugged them.

Many of my patients can't begin to see the extent of their deconditioning and reliance on others and they don't understand that some aspects of recovery can't be outsourced.

[Jo Bowyer]

Perception and Cognition Are Largely Independent, but Still Affect Each Other in Systematic Ways: Arguments from Evolution and the Consciousness-Attention Dissociation

http://journal.frontiersin.org/artic...017.00040/full

The main thesis of this paper is that two prevailing theories about cognitive penetration are too extreme, namely, the view that cognitive penetration is pervasive and the view that there is a sharp and fundamental distinction between cognition and perception, which precludes any type of cognitive penetration. These opposite views have clear merits and empirical support. To eliminate this puzzling situation, we present an alternative theoretical approach that incorporates the merits of these views into a broader and more nuanced explanatory framework. A key argument we present in favor of this framework concerns the evolution of intentionality and perceptual capacities. An implication of this argument is that cases of cognitive penetration must have evolved more recently and that this is compatible with the cognitive impenetrability of early perceptual stages of processing information. A theoretical approach that explains why this should be the case is the consciousness and attention dissociation framework. The paper discusses why concepts, particularly issues concerning concept acquisition, play an important role in the interaction between perception and cognition.

This is a difficult read but worth the struggle.

[Jo Bowyer]

Tourette syndrome in the context of evolution and behavioral ecology.

https://www.ncbi.nlm.nih.gov/pubmed/28110694

Abstract

Tourette syndrome, and the closely related spectrum of tic disorders, are inherited neuropsychiatric conditions characterized by the presence of repetitive and stereotyped movements. Tics are elicited by either environmental experiences or internal signals that instruct the basal ganglia to initiate automatic or procedural movements. In most vertebrates the basal ganglia encode instructions for habitually used sequences of motor movements that are essential to survival. Tic disorders may represent evolved phenotypes with a lower threshold for basal ganglia-directed actions. This may have produced a susceptibility to extraneous tics, but also produced fast-acting tactical solutions to immediate physical problems. During periods of nonstop movement, continual foraging, and sustained vigilance, it may have been advantageous to allow subcortical motor commands to intrude into ongoing motor activities. It is clear that the engrams for individual motor responses held in the basal ganglia are selected by converging cortical and subcortical inputs. This form of convergent action selection results in the selection of the most contextually reinforced actions. Today people with Tourette's have tics that seem arbitrary and inappropriate; however, this may be due to the vast discrepancies in reinforcement between the ancestral environment and the modern one. In prehistoric environments, the motor behaviors of individuals with tic disorders may have been appropriate in environmental context, and had ecological relevance in survival and self-promotion.

Performers and sports people may have tics, so may many on their way to work on the underground, some are so slight as to be almost un noticeable

[marcel]

A big collection
http://www.nature.com/collections/ffjxdjnlcq

Nature: human evolution archive

Human evolution has made headlines in Nature since Raymond Dart published the first description of Australopithecus africanus in 1925 (Nature 115, 195-199, 1925). Since then, Nature has published the biggest news of new fossil discoveries. Zinjanthropus, Homo habilis, Sahelanthropus, Ardipithecus, Turkana Boy, Lucy, bones from Atapuerca and Dmanisi, Tools from Turkana and Olduvai, Gona and Happisburgh, the genomes of Neanderthals and the still-enigmatic Denisovans, and not forgetting the remarkable hobbits from Flores - all these and many more have made their debuts in the pages of Nature. This resource offers the latest news and opinion from the Nature Publishing Group in this exciting and often contentious field, and constantly updated archive of research going back a decade.

[Jo Bowyer]

This is great Marcel, and there are one or two which are open access. Some of my broader minded patients are fascinated by human evolution and it's relevance to the way we life today.

[marcel]

Prehistoric Human Ancestor?
NYtimes JAN. 30, 2017

The creatures are the oldest known members of an ancient group called deuterostomes, said Simon Conway Morris, a paleontologist at Cambridge University in England and a member of the team. Deuterostomes, which lie pretty close to the base of the family tree of all animals, are ancestral not just to humans but to a wide array of animals ranging from sea urchins and starfish to the vast family of vertebrates.

https://www.nytimes.com/2017/01/30/s...all-mouth.html

Molecular clocks and the early evolution of metazoan nervous systems
2015

The timing of early animal evolution remains poorly resolved, yet remains critical for understanding nervous system evolution. Methods for estimating divergence times from sequence data have improved considerably, providing a more refined understanding of key divergences. The best molecular estimates point to the origin of metazoans and bilaterians tens to hundreds of millions of years earlier than their first appearances in the fossil record. Both the molecular and fossil records are compatible, however, with the possibility of tiny, unskeletonized, low energy budget animals during the Proterozoic that had planktonic, benthic, or meiofaunal lifestyles. Such animals would likely have had relatively simple nervous systems equipped primarily to detect food, avoid inhospitable environments and locate mates. The appearance of the first macropredators during the Cambrian would have changed the selective landscape dramatically, likely driving the evolution of complex sense organs, sophisticated sensory processing systems, and diverse effector systems involved in capturing prey and avoiding predation.

http://rstb.royalsocietypublishing.o.../1684/20150046

[Jo Bowyer]

The future is mixed-race....and so is the past.

https://aeon.co/essays/the-future-is...42fa3-69418129

Differences in physical traits between human populations accumulated slowly over tens of thousands of years. As people spread across the globe and adapted to local conditions, a combination of natural selection and cultural innovation led to physical distinctions. But these groups did not remain apart. Contact between groups, whether through trade or conflict, led to the exchange of both genes and ideas. Recent insights from the sequencing of hundreds of thousands of human genomes in the past decade have revealed that our species’ history has been punctuated by many episodes of migration and genetic exchange. The mixing of human groups is nothing new.

What is new is the rate of mixing currently underway. Globalisation means that our species is more mobile than ever before. International migration has reached record highs, as has the number of interracial marriages, leading to a surge of multiracial people such as Shewmake. While genetic differences between human populations do not fall neatly along racial lines, race nevertheless provides insight into the extent of population hybridisation currently underway. This reshuffling of human populations is affecting the very structure of the human gene pool.

[Jo Bowyer]

Ancient DNA reveals genetic 'continuity' between Stone Age, modern populations in East Asia

https://www.sciencedaily.com/release...0201142131.htm

In contrast to Western Europeans, new research finds contemporary East Asians are genetically much closer to the ancient hunter-gatherers that lived in the same region eight thousand years previously.

Genome-wide data from two early Neolithic East Asian individuals dating to 7700 years ago

http://advances.sciencemag.org/conte.../e1601877.full

Abstract

Ancient genomes have revolutionized our understanding of Holocene prehistory and, particularly, the Neolithic transition in western Eurasia. In contrast, East Asia has so far received little attention, despite representing a core region at which the Neolithic transition took place independently ~3 millennia after its onset in the Near East. We report genome-wide data from two hunter-gatherers from Devil’s Gate, an early Neolithic cave site (dated to ~7.7 thousand years ago) located in East Asia, on the border between Russia and Korea. Both of these individuals are genetically most similar to geographically close modern populations from the Amur Basin, all speaking Tungusic languages, and, in particular, to the Ulchi. The similarity to nearby modern populations and the low levels of additional genetic material in the Ulchi imply a high level of genetic continuity in this region during the Holocene, a pattern that markedly contrasts with that reported for Europe.

Ancient women found in Russian cave were close relatives of today’s indigenous population
http://www.sciencemag.org/news/2017/...ous-population

The ancient women were discovered in Chertovy Vorota Cave, known as Devil’s Gate Cave in English. The site was of particular interest to population geneticist Andrea Manica of the University of Cambridge in the United Kingdom because the skeletons of five humans were found with pottery, harpoons, and the remnants of nets and mats woven from twisted blades of wild sedge grass—which some (but not all) researchers consider a rudimentary form of early agriculture.

DNA was extracted from the teeth, inner ear bones, and other skull bones from two of the skeletons from Devil’s Cave, and Hungarian graduate student Veronika Siska was able to sequence enough of the nuclear genome to compare it to hundreds of genomes of modern Europeans and Asians. The team found that the two Devil’s Gate Cave women were most closely related to the Ulchi, indigenous people who today live a few hundred kilometers north of the cave in the Amur Basin where they have long fished, hunted, and grown some of their food. The ancient women also were related to other people who speak the remaining and endangered 75 or so Tungusic languages spoken by dwindling numbers of ethnic people in eastern Siberia and China. They were also related to a lesser extent to modern Koreans and Japanese.

The women also looked like people in the Amur Basin today—they had genes that suggest they had brown eyes; straight, thick hair; skin color similar to the Asian people; and shovel-shaped incisors, similar to Asians. They also were lactose intolerant, which meant they could not digest the sugars in milk—and probably did not herd animals that could be milked.

A famous 'ancestor' may be ousted from the human family

http://www.sciencemag.org/news/2017/...et_cid=1293290

A remarkably complete skeleton introduced in 2010 as “the best candidate” for the immediate ancestor of our genus Homo may just be a pretender. Instead of belonging to the human lineage, the new species of Australopithecus sediba is more closely related to other hominins from South Africa that are on a side branch of the human family tree, according to a new analysis of the fossil presented here last week at the annual meeting of the American Association of Physical Anthropologists.

When fossils from several individuals’ skeletons were found in a collapsed cave in Malapa, South Africa, in 2008, their discoverer, paleoanthropologist Lee Berger of the University of the Witwatersrand, noted that they helped fill a key gap in the fossil record 2 million to 3 million years ago when some upright-walking australopithecine evolved into the earliest member of our genus, Homo. But the oldest Homo fossils, at 2.4 million to 2.9 million years, are scrappy, and a half dozen more primitive hominins may have been walking around Africa at roughly the right time to be the ancestor. Researchers have hotly debated whether their direct ancestor was the famous 3.2-million-year-old fossil Lucy and her kind, Australopithecus afarensis from Ethiopia, or another australopithecine.

With its fossils dated to 1.98 million years ago, Au. sediba is too young to be directly ancestral to all members of the genus Homo. But Berger and his colleagues proposed in 2010, and again in 2013 in six papers in Science, that given the many humanlike traits in Au. sediba’s face, teeth, and body, the Malapa fossils were a better candidate than Lucy or other East African fossils to be ancestral to Homo erectus, a direct human ancestor that appeared 1.8 million years ago.

In a talk here, though, paleoanthropologist Bill Kimbel of Arizona State University in Tempe analyzed the most complete skull of Au. sediba and systematically shot down the features claimed to link it to early Homo. Kimbel noted that the skull was that of a juvenile—a “7th grader”—whose face and skull were still developing. In his analysis, with paleoanthropologist Yoel Rak of Tel Aviv University in Israel, he concluded that the child already showed traits that linked it most closely to the South African australopithecine Au. africanus, a species that lived in South Africa 3 million to 2.3 million years ago. And had it survived to adulthood, its humanlike facial traits would have changed to become even more like those of Au. africanus.

Update 26/04/2017




Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis

http://www.pnas.org/content/early/20...29114.abstract

Significance

The discovery of a 3.3 million-year-old partial skeleton of Australopithecus afarensis, from Dikika, Ethiopia, preserved all seven cervical (neck) vertebrae and provided the only known evidence for the presence of 12 thoracic (rib-bearing) vertebrae in hominins prior to 60,000 years ago. This skeleton has seven cervical and only 12 thoracic vertebrae like humans, rather than 13 like African apes. However, the anatomical transition from thoracic to lumbar (lower back) vertebral form occurs at the 11th thoracic segment. This distinctive pattern of vertebral segmentation, rare in modern apes and humans, is also seen in the three other early hominins for which this area is known, with the Dikika skeleton providing the earliest and most complete example.

Abstract

The evolution of the human pattern of axial segmentation has been the focus of considerable discussion in paleoanthropology. Although several complete lumbar vertebral columns are known for early hominins, to date, no complete cervical or thoracic series has been recovered. Several partial skeletons have revealed that the thoracolumbar transition in early hominins differed from that of most extant apes and humans. Australopithecus africanus, Australopithecus sediba, and Homo erectus all had zygapophyseal facets that shift from thoracic-like to lumbar-like at the penultimate rib-bearing level, rather than the ultimate rib-bearing level, as in most humans and extant African apes. What has not been clear is whether Australopithecus had 12 thoracic vertebrae as in most humans, or 13 as in most African apes, and where the position of the thoracolumbar transitional element was. The discovery, preparation, and synchrotron scanning of the Australopithecus afarensis partial skeleton DIK-1-1, from Dikika, Ethiopia, provides the only known complete hominin cervical and thoracic vertebral column before 60,000 years ago. DIK-1-1 is the only known Australopithecus skeleton to preserve all seven cervical vertebrae and provides evidence for 12 thoracic vertebrae with a transition in facet morphology at the 11th thoracic level. The location of this transition, one segment cranial to the ultimate rib-bearing vertebra, also occurs in all other early hominins and is higher than in most humans or extant apes. At 3.3 million years ago, the DIK-1-1 skeleton is the earliest example of this distinctive and unusual pattern of axial segmentation.

Australopithecus afarensis vertebrae Dikika segmentation thoracic

Update 23/05/2017




A find in Australia hints at very early human exit from Africa

http://www.sciencemag.org/news/2017/...et_cid=1449315

As archaeologist Chris Clarkson was excavating a rock shelter in northern Australia one day in 2015, May Nango of the aboriginal Mirarr group brought her grandchildren to look at the pit. She pointed to a spot near the back wall of the red sandstone cliff and told the children that it was a wonderful place for their ancestors—the "old people"—to sleep 65,000 years ago, says Clarkson of the University of Queensland in Brisbane, Australia.

Nango's tale was more than an aboriginal "dreamtime" story. She was one of the first to hear from Clarkson's team about new scientific dates for the Madjedbebe rock shelter in Australia's Arnhem Land, a region the Mirarr still call home. The dates, based on new excavations and state-of-the-art methods, push back the earliest solid evidence for humans in Australia by 10,000 to 20,000 years and suggest that modern humans left Africa earlier than had been thought. Published this week in Nature, the findings also hint at when modern humans interacted with other archaic humans.

This early date will force the field to "rethink fundamentally the whole issue of when our species started to colonize Asia," says archaeologist Robin Dennell of the University of Sheffield in the United Kingdom.

The timing of the peopling of Australia has been contentious for decades. Many archaeologists split into two camps, favoring settlement either 60,000 years ago or sometime after 50,000 years ago, depending on whether they trusted the dates from certain sites. Last year, geneticists analyzing DNA from living Aborigines joined the fray, but they came up with a wide range of dates, from 50,000 to 70,000 years ago.

The Madjedbebe rock shelter, formerly known as Malakunanja II, has always been central to the issue. Known for its striking rock art, researchers proposed in 1989 that the shelter was the oldest human occupation in Australia, after they dated sediments containing stone tools to 50,000 to 60,000 years ago using the then-experimental method of thermoluminescence. But skeptics suggested that the 1500 tools and other artifacts could have drifted downward over time in the sandy sediments or that animals or termites had disrupted the layers.

Because people must have traveled across the islands of Southeast Asia to get to Australia, the date suggests humans were moving through Indonesia at the same time as Homo floresiensis, the tiny extinct human nicknamed "the hobbit," was living on the island of Flores; the last date for that species is 60,000 years ago, although so far there's no evidence of encounters between humans and hobbits.

The authors also suggest the new date of 65,000 years for the peopling of Australia pushes back the time when modern humans coming out of Africa mated with archaic species in Asia, such as Neandertals and Denisovans. Living Aborigines carry traces of those two species' DNA, which their ancestors must have acquired by mixing somewhere in Asia before they reached Australia.

But such early mixing with Denisovans and Neandertals is at odds with genetic evidence from living Aborigines and nearby Melanesians, says population geneticist David Reich of Harvard University. Analyses of these people's DNA "confidently" suggests that the interbreeding happened only 45,000 to 53,000 years ago, Reich says. "If these [new] dates are correct, they must be from a human population that was largely replaced by the people who are the primary ancestors of today's Australians and New Guineans," he says. If so, today's Mirarr descend from a later migration.

That makes sense to archaeologist Jim O'Connell of the University of Utah in Salt Lake City, who has favored the later chronology. This is "the only reliable [early] date," he says. "I'd make the argument that the ancestor of [living] Australian Aboriginals and New Guineans got there later."

However, paleoanthropologist Michael Westaway of Griffith University in Brisbane still thinks there was only a single migration. He notes that genomic samples to date don't include Aborigines in northern Australia such as Nango and her family. Their DNA—or that of their ancestors—might help resolve the issue.

In any case, the glimpse of these ancient people's behavior thrills both scientists and Aborigines. "What a wonderfully sophisticated group of first colonists they must have been," says Westaway, a fact not lost on Nango. She proudly noted in a statement: "We are glad to see the old tools and paintings showing that we Mirarr have been caring for this land for so long."

Update 20/07/2017

[Jo Bowyer]

Does Depression Have an Evolutionary Purpose?

http://nautil.us/issue/45/power/does...a088d-60783245

Theories about the evolutionary function of depression are numerous.2 One of the most popular current ideas is the analytical rumination hypothesis. This idea was described most thoroughly in a long 2009 article by Paul Andrews, an evolutionary psychologist now at McMaster University, and J. Anderson Thomson, a psychiatrist at the University of Virginia Student Health Services.3 Andrews had noted that the physical and mental symptoms of depression appeared to form an organized system. There is anhedonia, the lack of pleasure or interest in most activities. There’s an increase in rumination, the obsessing over the source of one’s pain. There’s an increase in certain types of analytical ability. And there’s an uptick in REM sleep, a time when the brain consolidates memories.

Andrews sees these symptoms as a nonrandom assortment betraying evolutionary design. After all, why would a breakdown produce so synchronized a set of responses? And that design’s function, he argues, is to pull us away from the normal pursuits of life and focus us on understanding or solving the one underlying problem that triggered the depressive episode—say, a failed relationship. If something is broken in your life, you need to bear down and mend it. In this view, the disordered and extreme thinking that accompanies depression, which can leave you feeling worthless and make you catastrophize your circumstances, is needed to punch through everyday positive illusions and focus you on your problems. In a study of 61 depressed subjects, 4 out of 5 reported at least one upside to their rumination, including self-insight, problem solving, and the prevention of future mistakes.4

via @SimonGandevia