How human brains became so big

The human brain is disproportionately large. And while abundant grey matter confers certain intellectual advantages, sustaining a big brain is costly - consuming a fifth of energy in the human body.

Dr Diana Rivas displays a human brain on a working surface at the "Museum of Neuropathology" in Lima, Peru
[Credit: Ernesto Benavides/AFP]

It is an oddity that has long flummoxed scientists: while most organisms thrive with small brains, or none at all, the human species opted to sacrifice a degree of body growth for more cerebral capacity.

On Wednesday, researchers said they can finally reveal how and why this happened.

The human brain, they suggested, expanded mainly in response to environmental stresses that forced our species to come up with innovative solutions for food and shelter, and pass the lessons on to our offspring.

The finding challenges a popular theory that the thinking organ grew as social interactions between humans became more and more complex, a research duo wrote in the science journal Nature.

In fact, the inverse may be true.

"The findings are intriguing because they suggest that some aspects of social complexity are more likely to be consequences rather than causes of our large brain size," said paper co-author Mauricio Gonzalez-Forero of the University of St Andrews in Scotland.

"The large human brain is more likely to stem from ecological problem-solving and cumulative culture than it is from social manoeuvering."

From our ape-like Australopithecus ancestors to modern Homo sapiens, the human brain has tripled in size.

But feeding such a big brain has been suggested to come at the cost of slow body growth in childhood - leaving our young dependent and vulnerable for longer than other animals.

Brain over brawn?

Previous research found correlations between large brain size in species and complex social structures, living in challenging environments, and an ability to learn lessons from peers -- also described as "culture".

But no studies have been able to conclude whether these factors are the cause of brain expansion, or the result of it.

With colleague Andy Gardner, Gonzalez-Forero developed a mathematical model to measure whether being confronted with ecological and social problems has a measurable impact on brain growth, and if yes, how much.

Model "brains" were presented with ecological challenges -- finding prey in bad weather or in tough terrain, for example, preserving food to protect it against mold or heat spoilage, or storing water amid drought.

Social challenges were introduced too, to test the influence on brain growth of cooperation and competition between individuals and groups.

Interestingly, cooperation was associated with a decrease in brain size, the researchers said -- probably because it allows individuals to rely on each other's resources and to save energy by growing smaller brains themselves.

"We find that increasingly difficult ecological problems expand brains, but social demands fail to lead to human sized brains," Gonzalez-Forero told AFP.

But why did human brains grow more than those of other animals living in challenging environments?

Probably because of culture -- the ability to learn skills from others rather than having to figure everything out for ourselves.

"So, our results suggest that it is the interaction of hard ecology and culture that produced the human brain size," said Gonzalez-Forero.

Source: AFP [May 23, 2018]

'Uniquely human' muscles have been discovered in apes

Muscles once thought 'uniquely human' have been discovered in several ape species, challenging long-held theories on the origin and evolution of human soft tissues. The findings question the anthropocentric view that certain muscles evolved for the sole purpose of providing special adaptations for human traits, such as walking on two legs, tool use, vocal communication and facial expressions. Published in Frontiers in Ecology and Evolution, the study highlights that thorough knowledge of ape anatomy is necessary for a better understanding of human evolution.

Figure showing the striking similarities between the head muscles of common chimpanzees, bonobos
and humans: the very rare exceptions are those shown in colors and with text
[Credit: Rui Diogo]

"This study contradicts key dogmas about human evolution and our distinct place on the 'ladder of nature,'" says Rui Diogo, an Associate Professor in the Department of Anatomy at Howard University, Washington, USA. "Our detailed analysis shows that in fact, every muscle that has long-been accepted as 'uniquely human' and providing 'crucial singular functional adaptations' for our bipedalism, tool use and vocal and facial communications is actually present in the same or similar form in bonobos and other apes, such as common chimpanzees and gorillas."

Long-standing evolutionary theories are largely based on the bone structures of prehistoric specimens -- and, according to Diogo, also on the idea that humans are necessarily more special and complex than other animals. These theories suggest that certain muscles evolved in humans only, giving us our unique physical characteristics. However, verification of these theories has remained difficult due to scant descriptions of soft tissues in apes, which historically have mainly focused on only a few muscles in the head or limbs of a single specimen.

Diogo explains, "There is an understandable difficulty in finding primate, and particularly ape, specimens to dissect as they are so rare both in the wild and museums."

To find enough data to complete this research, Diogo compiled all previous information on ape anatomy based on studies with colleague Bernard Wood. He also conducted anatomical research on several bonobos that died of natural causes, together with colleagues at the University of Antwerp under the Bonobo Morphology Initiative 2016 - looking for the presence of seven different muscles thought to have evolved only in our species.

Diogo discovered that these seven muscles were present in apes in a similar or even exact form. For example the fibularis tertius muscle, said to be uniquely associated with human bipedalism (walking on two legs), was present in half the examined bonobos. Similarly, both the laryngeal muscle arytenoideus obliquus and the facial muscle risorius -- thought to have evolved for our uniquely sophisticated vocal and facial communication, respectively -- were present in at least some chimpanzees and/or gorillas.

These findings open crucial new directions for research and question our understanding of human evolution. "The picture emerging from this research is that the origin and evolution of human soft-tissue is clearly more complex -- and not as exceptional -- as first thought," says Diogo.

"We need a more thorough examination of why these muscles are present in apes and, in some cases, in just part of a population within a certain species," he says. "Are these muscles essential for the apes that have them, as adaptationist evolutionary scientists would argue? Or are they evolutionary neutral features related to how their bodies develop, or simply by-products of other features?"

He concludes, "Most theories of human evolution give the impression that humans are markedly distinct from apes anatomically, but these are unverifiable 'just-so stories'. The real evidence shows we are not so different overall. This study highlights that a thorough knowledge of ape anatomy is necessary for a better understanding of our own bodies and evolutionary history."

Source: Frontiers [May 23, 2018]

Scientists analyze first ancient human DNA from Southeast Asia

The first whole-genome analyses of ancient human DNA from Southeast Asia reveal that there were at least three major waves of human migration into the region over the last 50,000 years.

Field workers excavate ancient human remains at Man Bac, Vietnam, in 2007. DNA from skeletons at this site
was included in the current study [Credit: Lorna Tilley, Australian National University]

The research, published in Science, complements what is known from archaeological, historical and linguistic studies of Southeast Asia, defined as the area east of India and south of China.

The work illuminates another critical portion of the story of ancient population dynamics around the world, joining numerous ancient-DNA studies of Europe as well as burgeoning research from the Near East, Central Asia, Pacific Islands and Africa.

"A very important part of the world is now accessible for ancient DNA analysis," said Mark Lipson, a postdoctoral fellow in the lab of ancient-DNA specialist David Reich at Harvard Medical School and first author of the study. "It opens a window into the genetic origins of the people who lived there in the past and those who live there now."

An international team led by researchers at HMS and the University of Vienna extracted and analyzed DNA from the remains of 18 people who lived between about 4,100 and 1,700 years ago in what are now Vietnam, Thailand, Myanmar and Cambodia.

The team found that the first migration took place about 45,000 years ago, bringing in people who became hunter-gatherers.

Then, during the Neolithic Period, around 4,500 years ago, there was a large-scale influx of people from China who introduced farming practices to Southeast Asia and mixed with the local hunter-gatherers.

People today with this ancestry mix tend to speak Austroasiatic languages, leading the researchers to propose that the farmers who came from the north were early Austroasiatic speakers.

"This study reveals a complex interplay between archaeology, genetics and language, which is critical for understanding the history of Southeast Asian populations," said co-senior author Ron Pinhasi of the University of Vienna.

The research revealed that subsequent waves of migration during the Bronze Age, again from China, arrived in Myanmar by about 3,000 years ago, in Vietnam by 2,000 years ago and in Thailand within the last 1,000 years. These movements introduced ancestry types that are today associated with speakers of different languages.

The identification of three ancestral populations -- hunter-gatherers, first farmers and Bronze Age migrants -- echoes a pattern first uncovered in ancient DNA studies of Europeans, but with at least one major difference: Much of the ancestral diversity in Europe has faded over time as populations mingled, while Southeast Asian populations have retained far more variation.

"People who are nearly direct descendants of each of the three source populations are still living in the region today, including people with significant hunter-gatherer ancestry who live in Thailand, Malaysia, the Philippines and the Andaman Islands," said Reich, professor of genetics at HMS and co-senior author of the study. "Whereas in Europe, no one living today has more than a small fraction of ancestry from the European hunter-gatherers."

Reich hypothesizes that the high diversity of Southeast Asia today can be partly explained by the fact that farmers arrived much more recently than in Europe -- around 4,500 years ago compared with 8,000 years ago -- leaving less time for populations to mix and genetic variation to even out.

The new findings make it clear that the multiple waves of migration, each of which occurred during a key transition period of Southeast Asian history, shaped the genetics of the region to a remarkable extent.

"The major population turnover that came with the arrival of farmers is unsurprising, but the magnitudes of replacement during the Bronze Age are much higher than many people would have guessed," said Reich.

Also unexpected were the linguistic implications raised by analyses of the ancestry of people in western Indonesia.

"The evidence suggests that the first farmers of western Indonesia spoke Austroasiatic languages rather than the Austronesian languages spoken there today," Reich added. "Thus, Austronesian languages were probably later arrivals."

Additional samples from western Indonesia before and after 4,000 years ago should settle the question, Reich said.

Source: Harvard Medical School [May 17, 2018]

Does evolution make us or are we just drifting that way?

Evolution may be responsible for a range of complex traits, including height and waist-to-hip ratio, and diseases such as schizophrenia, research from The University of Queensland shows.

Credit: Shutterstock

The findings improve understanding of how natural selection shapes human populations, and could lead to better prevention, diagnosis and treatment of complex diseases through an enhanced knowledge of their underlying genetics.

The study, led by Professor Jian Yang from UQ’s Institute for Molecular Bioscience and Queensland Brain Institute, used more than 400,000 genetic samples from African, East Asian and European populations.

“Many human complex traits are concentrated in different populations around the world,” Professor Yang said.

“For example, populations in the Northern Hemisphere tend to get taller the further north you go, and European Americans have a lower body mass index (BMI) than African Americans, but higher than Chinese, Indonesians or Thais.

“Environmental factors currently play a role, but most complex traits have a genetic component.

“The question is whether or not these differences are the consequence of natural selection or simply the result of what we call ‘genetic drift’ – where gene mutations (also called genetic variants) become more or less frequent in a population by chance.”

Professor Yang and his colleagues set out to answer the question by testing to see if genetic variants were more differentiated across African, East Asian and European populations than expected under genetic drift.

They looked at a range of complex traits – including height, BMI, waist-to-hip ratio and cholesterol levels – and four common diseases – coronary artery disease, type II diabetes, Alzheimer’s disease and schizophrenia.

If genetic variants associated with a complex trait resulted from natural selection they should appear more frequently than expected under genetic drift.

The analysis supported this, showing that the genetic variants associated with height, weight-to-hip ratio and schizophrenia were more differentiated than expected by random drift.

The genetic variants expected to affect height were higher in Europeans than Africans and East Asians and were consistent with observed differences between the populations.

“Our research was made possible by the availability of massive banks of genetic information that are being harnessed to shed new light on modifiable health risks that underlie common diseases.”

The methods developed in the study, published in Nature Communications, are general and applicable to other complex traits.

Source: University of Queensland [May 16, 2018]

Where hominid brains are concerned, size doesn't matter

The recently-discovered species Homo naledi may have had a pint-sized brain, but that brain packed a big punch. New research by Ralph Holloway and colleagues - that include researchers from the University of the Witwatersrand, Johannesburg, South Africa - published in the Proceedings of the National Academy of Sciences examines the imprints of the brain upon the skulls of this species, called endocasts. The research highlights the humanlike shape of naledi's tiny brain, surprising scientists who studied the fossils. These findings draw further into question the long-held belief that human evolution was an inevitable march towards bigger, more complex brains.

The skulls of Homo naledi bear traces on their inside surfaces of the shape of naledi's brain. Only a third the size
of human brains, they nonetheless had some surprisingly humanlike features [Credit: John Hawks]

The discovery of Homo naledi by Professor Lee Berger of Wits University and his team at the Rising Star caves in the Cradle of Human Kind in 2013 was one of the largest hominin discoveries ever made and hailed as one of the most significant hominid discoveries of the 21st Century. Berger and Professor John Hawkes who was also part of the original Rising Star team who made the naledi discovery, as well as Professor Heather Garvin from Des Moines University in the US, are associated with the Evolutionary Studies Institute (ESI), based at Wits University. They are all co-authors of the current study.

In 2017, geologists demonstrated that this species existed in southern Africa between 236,000 and 335,000 years ago--potentially the same time that modern humans first emerged in Africa. This is a puzzle to scientists, who long held that there was only one species in Africa at this late time period - Homo sapiens. How did this species exist alongside others with brains three times its size? The new study suggests that naledi's behavior may have reflected the shape and structure of the brain more than its size.

Homo naledi endocast (top) with a curvature map (bottom) highlighting the sulci that are visible. The frontal
of naledi's brain looked very humanlike despite its small size [Credit: Heather Garvin]

The researchers pieced together traces of Homo naledi's brain shape from an extraordinary collection of skull fragments and partial crania, from at least five adult individuals. One of these bore a very clear imprint of the convolutions on the surface of the brain's left frontal lobe. "This is the skull I've been waiting for my whole career," said lead author Ralph Holloway, of Columbia University.

The anatomy of naledi's frontal lobe was similar to humans, and very different from great apes. Naledi wasn't alone. Other members of our genus, from Homo erectus to Homo habilis and the small-brained "hobbits", Homo floresiensis, also share features of the frontal lobe with living humans. But earlier human relatives, like Australopithecus africanus, had a much more apelike shape in this part of the brain, suggesting that functional changes in this brain region emerged with Homo. "It's too soon to speculate about language or communication in Homo naledi," said coauthor Shawn Hurst, "but today human language relies upon this brain region."

Evidence about the brain shape of Homo naledi comes from many partial skulls. The team used virtual methods
to understand how naledi's brain fits into the big picture [Credit: Heather Garvin]

The back of the brain also showed humanlike changes in naledi compared to more primitive hominins like Australopithecus. Human brains are usually asymmetrical, with the left brain displaced forward relative to the right. The team found signs of this asymmetry in one of the most complete naledi skull fragments. They also found hints that the visual area of the brain, in the back of the cortex, was relatively smaller in naledi than in chimpanzees--another humanlike trait.

The small brains of Homo naledi raise new questions about the evolution of human brain size. Big brains were costly to human ancestors, and some species may have paid the costs with richer diets, hunting and gathering, and longer childhoods. But that scenario doesn't seem to work well for Homo naledi, which had hands well-suited for toolmaking, long legs, humanlike feet, and teeth suggesting a high-quality diet. According to study coauthor John Hawks, "Naledi's brain seems like one you might predict for Homo habilis, two million years ago. But habilis didn't have such a tiny brain--naledi did."

A humanlike brain organisation might mean that naledi shared some behaviours with humans despite having a much smaller brain size. Lee Berger, a co-author on the paper, suggests that the recognition of naledi's small but complex brain will also have a significant impact on the study of African archaeology. "Archaeologists have been too quick to assume that complex stone tool industries were made by modern humans. With naledi being found in southern Africa, at the same time and place that the Middle Stone Age industry emerged, maybe we've had the story wrong the whole time."

Source: University of the Witwatersrand [May 14, 2018]

New tool predicts eye, hair and skin color from a DNA sample of an unidentified individual

An international team, led by scientists from the School of Science at IUPUI and Erasmus MC University Medical Center Rotterdam in the Netherlands, has developed a novel tool to accurately predict eye, hair and skin color from human biological material - even a small DNA sample - left, for example, at a crime scene or obtained from archaeological remains. This all-in-one pigmentation profile tool provides a physical description of the person in a way that has not previously been possible by generating all three pigment traits together using a freely available webtool.

An international team, led by scientists from the School of Science at IUPUI and Erasmus MC University Medical Center
 Rotterdam, has developed a novel tool to accurately predict eye, hair and skin color from human biological material.
The innovative high-probability and high-accuracy complete pigmentation profile webtool
is available online without charge [Credit: Walsh lab in School of Science at IUPUI]

The tool is designed to be used when standard forensic DNA profiling is not helpful because no reference DNA exists against which to compare the evidence sample.

The HIrisPlex-S DNA test system is capable of simultaneously predicting eye, hair and skin color phenotypes from DNA. Users, such as law enforcement officials or anthropologists, can enter relevant data using a laboratory DNA analysis tool, and the webtool will predict the pigment profile of the DNA donor.

"We have previously provided law enforcement and anthropologists with DNA tools for eye color and for combined eye and hair color, but skin color has been more difficult," said forensic geneticist Susan Walsh from IUPUI, who co-directed the study. "Importantly, we are directly predicting actual skin color divided into five subtypes - very pale, pale, intermediate, dark and dark to black - using DNA markers from the genes that determine an individual's skin coloration. This is not the same as identifying genetic ancestry. You might say it's more similar to specifying a paint color in a hardware store rather than denoting race or ethnicity.

"If anyone asks an eyewitness what they saw, the majority of time they mention hair color and skin color. What we are doing is using genetics to take an objective look at what they saw," Walsh said.

The innovative high-probability and high-accuracy complete pigmentation profile webtool is available online without charge.

The study, "HIrisPlex-S System for Eye, Hair and Skin Colour Prediction from DNA: Introduction and Forensic Developmental Validation," is published in the peer-reviewed journal Forensic Science International: Genetics.

"With our new HIrisPlex-S system, for the first time, forensic geneticists and genetic anthropologists are able to simultaneously generate eye, hair and skin color information from a DNA sample, including DNA of the low quality and quantity often found in forensic casework and anthropological studies," said Manfred Kayser of Erasmus MC, co-leader of the study.

Source: Indiana University-Purdue University Indianapolis School of Science [May 14, 2018]

How our ancestors with autistic traits led a revolution in Ice Age art

The ability to focus on detail, a common trait among people with autism, allowed realism to flourish in Ice Age art, according to researchers at the University of York.

Detailed illustrations of lions painted in the Chauvet Cave [Credit: WikiCommons]

Around 30,000 years ago realistic art suddenly flourished in Europe. Extremely accurate depictions of bears, bison, horses and lions decorate the walls of Ice Age archaeological sites such as Chauvet Cave in southern France.

LSD

Why our ice age ancestors created exceptionally realistic art rather than the very simple or stylised art of earlier modern humans has long perplexed researchers.

Many have argued that psychotropic drugs were behind the detailed illustrations. The popular idea that drugs might make people better at art led to a number of ethically-dubious studies in the 60s where participants were given art materials and LSD.

The authors of the new study discount that theory, arguing instead that individuals with “detail focus”, a trait linked to autism, kicked off an artistic movement that led to the proliferation of realistic cave drawings across Europe.

Realism

Lead author of the paper, Dr Penny Spikins from the Department of Archaeology at the University of York, said: “Detail focus is what determines whether you can draw realistically; you need it in order to be a talented realistic artist. This trait is found very commonly in people with autism and rarely occurs in people without it.

“We looked at the evidence from studies attempting to identify a link between artistic talent and drug use, and found that drugs can only serve to disinhibit individuals with a pre-existing ability. The idea that people with a high degree of detail focus, many of which may have had autism, set a trend for extreme realism in ice age art is a more convincing explanation.”

Focus

The research adds to a growing body of evidence that people with autistic traits played an important role in human evolution.

Dr Spikins added:  “Individuals with this trait – both those who would be diagnosed with autism in the modern day and those that wouldn’t – likely played an important part in human evolution and survival as we colonised Europe.

“As well as contributing to early culture, people with the attention to detail needed to paint realistic art would also have had the focus to create complex tools from materials such as bone, rock and wood. These skills became increasingly important in enabling us to adapt to the harsh environments we encountered in Europe.”

The study is published in Open Archaeology.

Author: Shelley Hughes | Source: University of York [May 14, 2018]

Hun migrations 'linked to deadly Justinian Plague'

Scientists say one of the deadliest plagues in history may be linked to the migration westward of the Hun peoples. The Justinian Plague, which struck in 541 AD, may have killed as many as 25 million.

A mass burial of battle victims from the Xiongnu period in Mongolia. The Xiongnu warriors are linked
to the nomadic people who would later become known as the Huns [Credit: BBC News]

Now, scientists say the outbreak probably originated in Asia, not Egypt as contemporary and more recent chroniclers had thought.

The finding comes from analysis of DNA found in 137 human skeletons unearthed on the Eurasian steppe.

The steppe region covers a vast area, spanning some 8,000km from Hungary to north-eastern China. The large sample of individuals covers a date range of 2,500 BC - 1,500 AD.

Writing in the journal Nature, Eske Willerslev, Peter de Barros Damgaard and others describe how they sequenced genomes from these individuals and, in two of them, recovered DNA from a strain of plague related to the one responsible for the Justinian Plague. A separate paper in the same edition of the journal describes the discovery of hepatitis B strains in ancient people from the Steppe.

The plague pandemic is named after Justinian I, who ruled the Eastern Roman Empire (also known as the Byzantine Empire) at the time of the initial outbreak. Indeed, it is said that Justinian himself caught the disease, but recovered.

The outbreak in Constantinople (which is now Istanbul in Turkey) was thought to have been carried to the city by rats on grain ships arriving from Egypt. While the plague was present in north-east Africa, the new research makes an origin in Central and Eastern Asia more likely.

The researchers say the plague probably moved westward with the migration of tribes who would become known to Roman chroniclers as the Huns.

Nomadic alliance

The Huns were not one people but formed from diverse nomadic groups such as the Scythians and the Xiongnu who forged allegiances to extend their power and territory. The Scythians were known to the Romans and Greeks as proficient horsemen living on the border between Europe and Asia. The Xiongnu are first attested further east, and fought a bloody war with the forces of Han dynasty China.

Detail of a contemporary portrait of Justinian I in the Basilica of San Vitale, Ravenna
[Credit: John Horgan/WikiCommons]

"In some of these Huns, we find the basic form of the Justinian Plague... that killed off millions of people in Europe," said co-author Eske Willerslev, from the University of Copenhagen.

DNA from a strain of the plague bacterium (Yersinia pestis) closely related to the one involved in the Justinian pandemic was found in a Hun individual from the Tian Shan mountains of Central Asia who died around 200 AD. This Tian Shan strain is also more "basal" than the Justinian form of the plague, meaning it is further back in the plague's genetic "family tree".

A relative of the Justinian Plague strain also turned up in an individual from North Ossetia, Russia, whose age is more uncertain, but who probably died between the sixth and ninth centuries AD.

The Huns probably began their westward movement in the second or third century BC, appearing on the borders of the Roman Empire in the fourth century. They established a short-lived dominion in Europe through the displacement of existing tribal groups and with attacks on the Empire itself.

Their ferocity was embodied by Attila, the Hunnic leader who fought numerous military campaigns against Rome.

Horses for watercourses

Co-author of the study Peter de Barros Damgaard told BBC News: "Our strain dates back to [around] 200 AD, so several hundreds of years before the Justinian plague wreaked Europe.

Hun warriors. Coloured engraving from 1890 [Credit: WikiCommons]

"An appearance has also been found in Egypt. As such, increased interaction under the Hunnic and later the Turk Khaganate would have aided in bringing this plague strain through the Silk Road.

"Intensified trade is a very likely factor."

DNA analysis of this plague strain shows it possessed mutations that would have allowed its transmission via fleas, much like the later Black Death. But whether this was the principal mode of spread in the sixth century outbreak remains unknown.

Dr Damgaard said: "An interesting speculation is that Xiongnu warriors are documented through ancient Chinese historical sources to have used biological warfare by putting dead horse bodies in water sources.

"I like to speculate that this would have been the breeding ground for plague, and once again the human trajectory would have been linked to horses, but I have no way of proving that."

Another paper in Nature, also led by Eske Willerslev, reports the oldest evidence of hepatitis B viruses (HBV) in humans. The findings come from viral sequences recovered from 12 ancient people on the steppe.

Barbara Mühlemann, a co-author from the University of Cambridge, UK, said: "People have tried to unravel the history of HBV for decades - this study transforms our understanding of the virus and proves it affected people as far back as the Bronze Age.

"We have also shown that it is possible to recover viral sequences from samples of this age which will have much wider scientific implications."

In 2015, some 257 million people were estimated to be infected with HBV; some 887,000 died due to complications such as liver cancer.

Author: Paul Rincon | Source: BBC News Website [May 11, 2018]

A European origin for leprosy?

New research by an international team including scientists from the Max Planck Institute for the Science of Human History, the University of Tübingen, EPFL Lausanne and the University of Zurich has revealed that there was much more diversity in the leprosy strains circulating in Medieval Europe than previously thought. This finding, based on the sequencing of 10 new ancient genomes from the leprosy-causing bacterium Mycobacterium leprae, complicates prior assumptions about the origin and spread of the disease, and also includes the oldest M. leprae genome sequenced to date, from about 400 AD in the United Kingdom.

Skeletal remains showing evidence of leprosy from the Odense St. Jørgen cemetery in Denmark, which
was established in 1270 and existed until 1560 [Credit: Dorthe Dangvard Pedersen]

Leprosy is one of the oldest recorded and most stigmatized diseases in human history. The disease was prevalent in Europe until the 16th century and is still endemic in many countries, with over 200,000 new cases reported annually. The bacterium Mycobacterium leprae is the main cause of leprosy. Previous research on the bacterium suggested that it clusters into several strains, only two of which were present in Medieval Europe. The present study, published in the journal PLOS Pathogens, aimed to further investigate the history and origin of M. leprae by looking for genetic evidence from a large number of ancient samples from throughout Europe.

10 new ancient genomes of M. leprae dating from approximately 400-1400 AD

The current study examined approximately 90 individuals with skeletal deformations that were characteristic of leprosy, from across Europe and from time periods ranging from approximately 400 AD to 1400 AD. From these samples, 10 new medieval M. leprae genomes were fully reconstructed. These genomes represent all known strains, including strains that are today associated with different locations around the globe, including Asia, Africa and the Americas. Additionally, in this study multiple strains were often found in the same cemetery, illustrating the diversity of the leprosy strains circulating throughout the continent at the time.

Skeletal remains from Great Chesterford showing evidence of leprosy. This is the oldest
 known case of leprosy in the United Kingdom [Credit: Sarah Inskip]

"We found much more genetic diversity in ancient Europe than expected," explains Johannes Krause, senior author of the study and a director at the Max Planck Institute for the Science of Human History. "Additionally, we found that all known strains of leprosy are present in Medieval Europe, suggesting that leprosy may already have been widespread throughout Asia and Europe in antiquity or that it might have originated western Eurasia."

Oldest leprosy genome to date

One M. leprae genome reconstructed by the team was from Great Chesterford, England, and dates to between 415-545 AD. This is the oldest M. leprae genome sequenced to date and comes from one of the oldest known cases of leprosy in the United Kingdom. Interestingly, this strain is the same found in modern-day red squirrels and supports the hypothesis that squirrels and the squirrel fur trade were a factor in the spread of leprosy among humans in Europe during the medieval period.

Verena Schuenemann at the Palaeogenetics Laboratory,
University of Tuebingen [Credit: Johannes Krause]

"The dynamics of M. leprae transmission throughout human history are not fully resolved. Characterization and geographic association of the most ancestral strains are crucial for deciphering leprosy's exact origin" states lead author Verena Schuenemann of the University of Zurich. "While we have some written records of leprosy cases that predate the Common Era, none of these have yet been confirmed on a molecular level."

The abundance of ancient genomes in the current study has resulted in a new and older estimate for the age of M. leprae than previous studies, placing its age at least a few thousand years old. "Having more ancient genomes in a dating analysis will result in more accurate estimates," explains Krause. "The next step is to search for even older osteological cases of leprosy than currently available, using well-established methods for identification of potential cases."

Source: Max Planck Society [May 10, 2018]

Stone Age hepatitis B virus decoded

An international team of scientists led by researchers at the Max Planck Institute for the Science of Human History and the University of Kiel has successfully reconstructed genomes from Stone Age and Medieval European strains of the hepatitis B virus. This unprecedented recovery of ancient virus DNA indicates that hepatitis B was circulating in Europe at least 7000 years ago. While the ancient virus is similar to its modern counterparts, the strains represent a distinct lineage that has likely gone extinct and is most closely related to chimpanzee and gorilla viruses.

Skeletal remains of HBV positive individual from the Stone Age site of Karsdorf, Germany. The individual
was a male with an age at death of around 25-30 years [Credit: Nicole Nicklisch]

The hepatitis B virus (HBV) is one of the most widespread human pathogens known today, affecting over 250 million people worldwide. However, its origin and evolutionary history remain unclear. Studying the evolution and history of the virus has to date been especially difficult, because until now viral DNA had not been successfully recovered from prehistoric samples. In the present study, which has been published in eLife, an international team of researchers led by the Max Planck Institute for the Science of Human History and the Institute of Clinical Molecular Biology at Kiel University, not only recovered ancient viral DNA from skeletons but also reconstructed the genomes of three strains of HBV.

The ancient history of hepatitis B

For this study, the researchers analyzed samples from the teeth of 53 skeletons excavated from Neolithic and medieval sites in Germany. The remains dated from around 5000 BC to 1200 AD. The researchers screened all samples for viral pathogens and detected ancient HBV in three of the individuals.

Geographic location of the samples from which ancient HBV genomes were recovered. Icons indicate the sample
material (tooth or mummy). HBV genomes obtained in this study are indicated by black frame
[Credit: Krause-Kyora et al. eLife 2018]

Full HBV genomes were recovered from these samples, two of which were from the Neolithic period, dating to about 7000 and 5000 years ago, and one from the medieval period. The Neolithic genomes represent the by far oldest virus genomes reconstructed to date.

Interestingly, the ancient virus genomes appear to represent distinct lineages that have no close relatives today and possibly went extinct. The two Neolithic genomes, although recovered from individuals that lived 2000 years apart, were relatively similar to each other in comparison with modern strains, and were in fact more closely related to modern strains of HBV found in Chimpanzees and Gorillas. In contrast, the medieval HBV genome is more similar to modern strains, but still represents a separate lineage.

This is the case even when it is compared to two previously published HBV genomes recovered from mummies dating to the 16th century. The HBV strains found in these mummies are closely related to modern strains, suggesting a surprising lack of change in the virus over the last 500 years. These findings point to a complicated history for the virus, which may have involved multiple cross-species transmission events.

Skeletal remains of HBV positive individual from the medieval site of Petersberg, Germany. The individual
was a male with an age at death of around 65-70 years [Credit: Ben Krause-Kyora]

Long and complicated evolution of one of today's most common viruses

"Taken together, our results demonstrate that HBV already existed in Europeans 7000 years ago and that its genomic structure closely resembled that of modern hepatitis B viruses, despite the differences observed," explains first author Ben Krause-Kyora, of the Max Planck Institute for the Science of Human History and Kiel University. "More ancient precursors, intermediates and modern strains of both human and non-human primate HBV strains need to be sequenced to disentangle the complex evolution of this virus," he adds.

New tool for studying the evolution of blood-borne viruses

Johannes Krause, senior author and director of the Department of Archaeogenetics at the Max Planck Institute for the Science of Human History, emphasizes the most important implication of the study. "Our results reveal the great potential of ancient DNA from human skeletons to allow us to study the evolution of blood-borne viruses. Previously, there was doubt as to whether we would ever be able to study these diseases directly in the past," he explains. "We now have a powerful tool to explore the deep evolutionary history of viral diseases."

Source: Max Planck Institute for the Science of Human History [May 10, 2018]