The Great London:
Human Evolution

Researchers have observed wild-bearded capuchin monkeys in Brazil deliberately break stones, unintentionally creating flakes that share many of the characteristics of those produced by early Stone Age hominins. The difference is that the capuchins' flakes are not intentional tools for cutting and scraping, but seem to be the by-product of hammering or 'percussive behaviour' that the monkeys engage in to extract minerals or lichen from the stones.

In a paper, >published in Nature, the research team says this finding is significant because archaeologists had always understood that the production of multiple stone flakes with characteristics such as conchoidal fractures and sharp cutting edges was a behaviour unique to hominins. The paper suggests that scholars may have to refine their criteria for identifying intentionally produced early stone flakes made by hominins, given capuchins have been observed unintentionally making similar tools.

The research is authored by researchers from the University of Oxford, University College London and University of Sao Paulo in Brazil. The team observed individual monkeys in Serra da Capivara National Park unintentionally creating fractured flakes and cores. While hominins made stone flake tools for cutting and butchery tasks, the researchers admit that it is unclear why monkeys perform this behaviour. They suggest that the capuchins may be trying to extract powdered silicon (known to be an essential trace nutrient) or to remove lichen for some as yet unknown medicinal purpose. At no point did the monkeys try to cut or scrape using the flakes, says the study.

Lead author Dr Tomos Proffitt, from the School of Archaeology at the University of Oxford, comments: 'Within the last decade, studies have shown that the use and intentional production of sharp-edged flakes are not necessarily linked to early humans (the genus Homo) who are our direct relatives, but instead were used and produced by a wider range of hominins. However, this study goes one step further in showing that modern primates can produce archaeologically identifiable flakes and cores with features that we thought were unique to hominins.

'This does not mean that the earliest archaeological material in East Africa was not made by hominins. It does, however, raise interesting questions about the possible ways this stone tool technology developed before the earliest examples in the archaeological record appeared. It also tells us what this stone tool technology might look like. There are important questions too about the uniqueness of early hominin behaviour. These findings challenge previous ideas about the minimum level of cognitive and morphological complexity required to produce numerous conchoidal flakes.'

The monkeys were observed engaging in 'stone on stone percussion', whereby they individually selected rounded quartzite cobbles and then using one or two hands struck the 'hammer-stone' forcefully and repeatedly on quartzite cobbles embedded in a cliff face. This action crushed the surface and dislodged cobbled stones, and the hand-held 'hammer stones' became unintentionally fractured, leaving an identifiable primate archaeological record. As well as using the active hammer-stone to crush 'passive hammers' (stones embedded in the outcrop), the capuchins were also observed re-using broken hammer-stones as 'fresh' hammers.

The research team examined 111 fragmented stones collected from the ground immediately after the capuchins had dropped them, as well as from the surface and excavated areas in the site. They gathered complete and broken hammer-stones, complete and fragmented flakes and passive hammers. Around half of the fractured flakes exhibited conchoidal fracture, which is typically associated with the hominin production of flakes.

Bearded capuchins and some Japanese macaques are known to pound stones directly against each other, but the paper remarks that the capuchins in Serra da Capivara National Park are the only wild primates to be observed doing this for the purpose of damaging the stones.

Co-author and leader of the Primate Archaeology (Primarch) project Michael Haslam, from the University of Oxford, says: 'Our understanding of the new technologies adopted by our early ancestors helps shape our view of human evolution. The emergence of sharp-edged stone tools that were fashioned and hammered to create a cutting tool was a big part of that story. The fact that we have discovered monkeys can produce the same result does throw a bit of a spanner in the works in our thinking on evolutionary behaviour and how we attribute such artefacts. While humans are not unique in making this technology, the manner in which they used them is still very different to what the monkeys seem capable of.'

Source: University of Oxford [October 19, 2016]

A genetic mutation in extinct European apes that enabled them to convert fruit sugar into fat could be a cause of the modern obesity epidemic and diabetes, according to scientists. Fossil evidence reveals that apes living around 16 million years ago, in what was then subtropical Europe, began to suffer as global cooling subsequently changed the forest, making the fruit they ate scarce.

Experts suggest that a mutation in the uricase gene which helps to convert fruit sugar (fructose) occurred around 15 million years ago. This aided apes in adding on fat layers so they could survive famines and harsh winters.

Persistence of the same mutation in all modern great apes and all modern humans, along with the fossil evidence, suggests that the now extinct European apes evolved into today's great apes and the earliest hominids.

Scientists have spent decades researching the genetic causes of obesity which is rarely found in other animals – apart from domesticated pets. The latest research focuses on fructose: a sugar which breaks down to form uric acid in the blood, according to a Sunday Times report.

The Western diet contains so much uric acid that it cannot be removed quickly enough, but triggers liver cells to turn fructose into fat, with the effect of humans adding on extra weight. The uricase mutation predisposes humans to obesity and diabetes in modern times. The results suggest a need to eat and drink much less fructose to fight obesity and prevent its dangerous complications.

"The gene enables uric acid levels to spike in response to two types of food," wrote Peter Andrews, professor of anthropology at University College London in Scientific American, co-authored with Richard Johnson, a professor of medicine in the US. "Those like beer that produce a lot of uric acid [directly] and those that contain a lot of fructose. These include honey and processed food that are high in table sugar or high-fructose corn syrup. When uric acid spikes we become susceptible to obesity and diabetes."

Obesity is considered as one of the biggest public health challenges of the century. Statistics show that it is affecting more than 500 million people worldwide. In the US alone, obesity costs at least $200 billion each year.

This medical condition also contributes to potentially fatal disorders such as cancer, type 2 diabetes and cardiovascular disease.

Author: Fiona Keating | Source: International Business Times [November 20, 2015]

A new UCL study examines how the baculum (penis bone) evolved in mammals and explores its possible function in primates and carnivores—groups where many species have a baculum, but some do not.

The baculum has been described as "the most diverse of all bones", varying dramatically in length, width and shape in the male mammals where it is present.

The research, published today in the Royal Society journal >Proceedings of the Royal Society B, shows that the ancestral mammal, like humans, did not have a baculum - but both ancestral primates and carnivores did. The work uncovers that the baculum first evolved in mammals between 145 and 95 million years ago.

The study found that prolonged intromission - defined as penetration for longer than 3 minutes - was correlated with baculum presence across the course of primate evolution. Prolonged intromission was also found to predict a longer baculum in primates and carnivores.

High levels of postcopulatory sexual competition between males also predicted longer bacula in primates.

First author, Matilda Brindle (UCL Anthropology), said: "Our findings suggest that the baculum plays an important role in supporting male reproductive strategies in species where males face high levels of postcopulatory sexual competition. Prolonging intromission helps a male to guard a female from mating with any competitors, increasing his chances of passing on his genetic material."

The findings of the study may also provide clues as to why humans do not have a baculum.

When any cultural aspects of sex are removed and a male's aim is solely to ejaculate, humans have a short intromission duration.

In species where mating occurs between multiple males and multiple females (known as polygamy), there is acute competition between males to fertilise a female. However, human mating systems are not like this. Instead humans tend to be monogamous or, more rarely, polygynous (where one male mates with multiple females). In these circumstances, only one male has access to a female and postcopulatory competition between males is absent or very low level.

Brindle added: "Interestingly, humans have neither prolonged intromission durations, nor high levels of postcopulatory sexual competition. Given the results of our study, this may help to unravel the mystery of why the baculum was lost in the human lineage."

Chimpanzees and bonobos, humans' closest relatives, have very small bacula (between about 6-8mm) and short intromission durations (around 7 seconds for chimpanzees and 15 seconds for bonobos). However, they are characterised by polygamous mating systems, so they experience high levels of postcopulatory competition between males. The researchers suggest that this may be why these species have retained a baculum - albeit a small one.

Co-author, Dr Kit Opie (UCL Anthropology), commented: "After the human lineage split from chimpanzees and bonobos and our mating system shifted towards monogamy, probably after 2mya, the evolutionary pressures retaining the baculum likely disappeared. This may have been the final nail in the coffin for the already diminished baculum, which was then lost in ancestral humans."

Source: University College London [December 14, 2016]

Genes that drive the shape of human noses have been identified by a UCL-led study. The four genes mainly affect the width and 'pointiness' of noses which vary greatly between different populations. The new information adds to our understanding of how the human face evolved and may help contribute to forensic DNA technologies that build visual profiles based on an individual's genetic makeup.

The study, published today in >Nature Communications, analysed a population of over 6,000 people with varied ancestry across Latin America to study the differences in normal facial features and identify the genes which control the shape of the nose and chin.

The researchers identified five genes which play a role in controlling the shape of specific facial features. DCHS2, RUNX2, GLI3 and PAX1 affect the width and pointiness of the nose and another gene -- EDAR -- affects chin protrusion.

"Few studies have looked at how normal facial features develop and those that have only looked at European populations, which show less diversity than the group we studied. What we've found are specific genes which influence the shape and size of individual features, which hasn't been seen before.

"Finding out the role each gene plays helps us to piece together the evolutionary path from Neanderthal to modern humans. It brings us closer to understanding how genes influence the way we look, which is important for forensics applications," said the first author of the report, Dr Kaustubh Adhikari, UCL Cell & Developmental Biology.

People have different shaped facial features based on their genetic heritage and this is partly due to how the environment influenced the evolution of the human genome. The nose, for example, is important for regulating the temperature and humidity of the air we breathe in so developed different shapes in warmer and cooler climates.

"It has long been speculated that the shape of the nose reflects the environment in which humans evolved. For example, the comparatively narrower nose of Europeans has been proposed to represent an adaptation to a cold, dry climate. Identifying genes affecting nose shape provides us with new tools to examine this question, as well as the evolution of the face in other species. It may also help us understand what goes wrong in genetic disorders involving facial abnormalities," explained Professor Andrés Ruiz-Linares UCL Biosciences, who led the study.

The team collected and analysed DNA samples from 6,630 volunteers from the CANDELA cohort recruited in Brazil, Colombia, Chile, Mexico and Peru. After an initial screen, a sample size of 5,958 was used. This group included individuals of mixed European (50%), Native American (45%) and African (5%) ancestry, resulting in a large variation in facial features.

Both men and women were assessed for 14 different facial features and whole genome analysis identified the genes driving differences in appearance.

A subgroup of 3,000 individuals had their features assessed using a 3D reconstruction of the face in order to obtain exact measurements of facial features and the results identified the same genes.

The study identified genes that are involved in bone and cartilage growth and the development of the face. GLI3, DCHS2 and PAX1 are all genes known to drive cartilage growth -- GLI3 gave the strongest signal for controlling the breadth of nostrils, DCHS2 was found to control nose 'pointiness' and PAX1 also influences nostril breadth. RUNX2 which drives bone growth was seen to control nose bridge width.

The genes GLI3, DCHS2 and RUNX2 are known to show strong signals of recent selection in modern humans compared to archaic humans such as Neanderthals and Denisovans; GLI3 in particular undergoing rapid evolution.

Source: University College London [May 19, 2016]

Consider the engineering marvel that is your foot. Be it hairy or homely, without its solid support you'd be hard-pressed to walk or jump normally.

Now, researchers at the Stanford University School of Medicine and the HudsonAlpha Institute for Biotechnology in Huntsville, Alabama, have identified a change in gene expression between humans and primates that may have helped give us this edge when it comes to walking upright. And they did it by studying a tiny fish called the threespine stickleback that has evolved radically different skeletal structures to match environments around the world.

"It's somewhat unusual to have a research project that spans from fish all the way to humans, but it's clear that tweaking the expression levels of molecules called bone morphogenetic proteins can result in significant changes not just in the skeletal armor of the stickleback, but also in the hind-limb development of humans and primates," said David Kingsley, PhD, professor of developmental biology at Stanford. "This change is likely part of the reason why we've evolved from having a grasping hind foot like a chimp to a weight-bearing structure that allows us to walk on two legs."

Kingsley, who is also a Howard Hughes Medical Institute investigator, is the senior author of a paper describing the work that will be >published in Cell. The lead author is former Stanford postdoctoral scholar Vahan Indjeian, PhD, now head of a research group at Imperial College London.

Adapting to different environments

The threespine stickleback is remarkable in that it has evolved to have many different body structures to equip it for life in different parts of the world. It sports an exterior of bony plates and spines that act as armor to protect it from predators. In marine environments, the plates are large and thick; in freshwater, the fish have evolved to have smaller, lighter-weight plates, perhaps to enhance buoyancy, increase body flexibility and better slip out of the grasp of large, hungry insects. Kingsley and his colleagues wanted to identify the regions of the fish's genome responsible for the skeletal differences that have evolved in natural populations.

The researchers identified the area of the genome responsible for controlling armor plate size, and then looked for differences there in 11 pairs of marine and freshwater fish with varying armor-plate sizes. They homed in on a region that includes the gene for a bone morphogenetic protein family member called GDF6. Due to changes in the regulatory DNA sequence near this gene, freshwater sticklebacks express higher levels of GDF6, while their saltwater cousins express less. Strikingly, marine fish genetically engineered to contain the regulatory sequence of freshwater fish expressed higher levels of GDF6 and developed smaller armor plates, the researchers found.

Regulatory regions in humans vs. chimps

Kingsley and his colleagues wondered whether changes in GDF6 expression levels might also have contributed to critical skeletal modifications during human evolution. The possibility was not as far-fetched as it might seem. Other studies by evolutionary biologists, including Kingsley, have shown that small changes in the regulatory regions of key developmental genes can have profound effects in many vertebrates.

They began by working with colleagues in the laboratory of Gill Bejerano, PhD, Stanford associate professor of developmental biology, of computer science and of pediatrics, to compare differences in the genomes of chimps and humans. In previous surveys, they found over 500 places in which humans have lost regulatory regions that are conserved from chimps and many other mammals. Two of these occur near the GDF6 gene. They homed in on one in particular.

"This regulatory information was shared through about 100 million years of evolution," said Kingsley. "And yet, surprisingly, this region is missing in humans."

To learn more about what the GDF6 regulatory region might be controlling, the researchers used the chimp regulatory DNA to control the production of a protein that is easy to visualize in mice. Laboratory mice with the chimp regulatory DNA coupled to the reporter protein strongly and specifically expressed the protein in their hind limbs, but not their forelimbs, and in their lateral toes, but not the big toes of the hind limbs. Mice genetically engineered to lack the ability to produce GDF6 in any part of their bodies had skull bones that were smaller than normal and their toes were shorter than those of their peers. Together, these findings gave the researchers a clue that GDF6 might play a critical role in limb development and evolution.

The big toe: an explanation

The fact that humans are missing the hind-limb-regulatory region probably means that we express less of the gene in our legs and feet during development, but comparable amounts in our nascent arms, hands and skulls. Loss of this particular regulatory sequence would also shorten lateral toes but not the first toe of feet. This may help explain why the big toe is aligned with other short, lateral toes in humans. Such a modification would create a more sturdy foot with which to walk upright.

"These bone morphogenetic proteins are strong signals for bone and cartilage growth in all types of animals," said Kingsley.

"You can evolve new skeletal structures by changing where and when the signals are expressed, and it's very satisfying to see similar regulatory principles in action whether you are changing the armor of a stickleback, or changing specific hind-limb structures during human evolution."

Author: Krista Conger | Source: Stanford University Medical Center [January 07, 2016]

A research team led by scientists of the Max Planck Institute for Evolutionary Anthropology scanned the skulls of Neandertals and found the small middle ear ossicles, which are important for hearing, still preserved within the cavities of the ear. To their surprise, the Neandertal ossicles are morphologically distinct from the ossicles of modern humans. Despite the differences in morphology, the function of the middle ear is largely the same in the two human species.

The authors relate the morphological differences in the ossicles to different evolutionary trajectories in brain size increase and suggest that these findings might be indicative of consistent aspects of vocal communication in modern humans and Neandertals. These findings are also of importance for shedding light on the emergence of human spoken language, which can only be inferred indirectly from the archaeological and fossil record.

The three bones of the middle ear (hammer, anvil, stapes) make up the ossicular chain. This bony chain, which is found in all mammals is dedicated to the transmission of sound waves from the tympanic membrane to the inner ear and helps in amplifying the energy of airborne sound in order to allow the sound wave to travel within the fluid-filled inner ear.

Moreover, the ear ossicles are not only important for correct hearing but are also the smallest bones of our body. Thus, it does not surprise that the ossicles are among the most rarely found bones in the mammalian fossil record including the one of human ancestors. Given their important role in audition this lack of knowledge has ever been frustrating for researchers interested in studying hearing capacities of extinct species.

Tiny bones still present

This also applies to our closest extinct relatives - the Neandertals whose communicative capacities including existence of human spoken language is a major scientific debate ever since the first discovery of Neandertal remains. A research team led by Alexander Stoessel from the Max Planck Institute for Evolutionary Anthropology in Leipzig used high-resolution computer tomography scans of Neandertal skulls and systematically checked for ossicles that potentially became trapped within the cavity of the middle ear.

And indeed, the researchers found ear ossicles in 14 Neandertal individuals coming from sites in France, Germany, Croatia and Israel, resulting in the largest sample of ear ossicles of any fossil human species. “We were really astonished how often the ear ossicles are actually present in these fossil remains, particularly when the ear became filled with sediments” says lead researcher Alexander Stoessel.

After virtually reconstructing the bones, the team - which also included scientist from the Friedrich-Schiller University in Jena and the University College in London – compared them to ossicles of anatomically modern humans and also chimpanzees and gorillas which are our closest living relatives.

Since ossicles are not only small but also complex-shaped the researchers compared them by means of three-dimensional analysis that uses a much larger number of measuring points allowing for examination of the three-dimensional shape of a structure. “Despite the close relationship between anatomically modern humans and Neandertals to our surprise the ear ossicles are very differently shaped between the two human species” says Romain David who was involved in the study.

Based on the results of the morphological comparison the research team examined the potential reasons for these different morphologies. In order to see if these differences may affect hearing capacity of Neandertals and modern humans or reflects a tight relationship with the base of the skull they also analyzed the structures surrounding the ear ossicles. The outcome of this analysis was surprising, again since the functional parameters of the Neandertal and modern human middle ear are largely similar despite contrasting morphologies.

Similar communication skills in archaic humans

Instead, the team found the ear ossicles strongly related to the morphology of the surrounding cranial structures which also differ between the two human groups. The reseachers attribute these differences to different evolutionary trajectories that Neandertals and modern humans pursued in order to increase their brain volume which also impacted the structures of the cranial base which the middle ear is a part of.

“For us these results could be indicative for consistent aspects of vocal communication in anatomically modern humans and Neandertals that were already present in their common ancestor” says Jean-Jacques Hublin who is an author of this study and continues “these findings should be a basis for continuing research on the nature of the spoken language in archaic hominins”.

The findings are published in >Proceedings of the National Academy of Sciences.

Source: Max Planck Institute for Evolutionary Anthropology [September 27, 2016]

Long before the advent of social media, human social networks were built around sharing a much more essential commodity: food. Now, researchers reporting on the food sharing networks of two contemporary groups of hunter-gatherers in the >Cell Press journal Current Biology provide new insight into fundamental nature of human social organization.

The new work reveals surprising similarities between the Agta of the Philippines and Mbendjele of the Republic of Congo. In both places, individuals maintain a three-tiered social network that appears to buffer them against day-to-day shortfalls in foraging returns.

"Previous research has suggested that social networks across human cultures are structured in similar ways," says Mark Dyble of University College London. "Across societies, there appear to be similar limits on the number of social relationships individuals are able to maintain, and many societies are said to have a 'multilevel' structure. Our work on contemporary hunter-gatherer groups sheds light on how this distinctive social structure may have benefited humans in our hunting-and-gathering past."

While previous studies have identified similarities in social structure across hunter-gatherer populations, the researchers say that the new work is the first to explore how hunter-gatherers' distinctive, "multilevel" social organization structures social life and cooperation in important activities such as foraging and food sharing.

"No other apes share food to the extent that humans do," says Andrea Migliano, principal investigator of the Leverhulme Trust-funded Hunter-Gatherers Resilience Project. "Hunter-gatherers' multi-level social structure exists in different groups, to help regulate these cooperative systems. Furthermore, multi-level social structures regulate social rules, friendship and kinship ties, and the spread of social norms, promoting a more efficient sharing and cooperation. Sharing is a crucial adaptation to hunter-gatherers' lifestyles, central to their resilience -- and central to the evolution of mankind."

The Agta live in northeast Luzon, Philippines. Their primary source of protein is fish, supplemented by inter-tidal foraging, hunting, honey collecting, and gathering of wild foods. The Mbendjele live in an area spanning northern Republic of Congo and southern Central African Republic, where they hunt for meat in the forest. Both groups also trade wild-caught meat or fish for cultivated foods, including rice and manioc.

Dyble, Migliano, and their colleagues collected data on food sharing by living with the two communities for many months, making observations on how often households shared food with each other. From this they constructed social networks of food sharing.

"Although we had an idea of how camps split into food sharing clusters 'on the ground,' we were able to test these using algorithms which are able to identify sub-communities within the nine camps we studied," Dyble explains.

Their analysis showed that food sharing is closely related to social organization. In both communities, individuals maintain a three-tiered social network. First is their immediate household, most often consisting of five or six individuals, second is a cluster of three to four closely related households who share food frequently, and third is the wider camp.

"Despite being from different continents and living in very different ecologies, both groups of hunter-gatherers had a strikingly similar social organization," Dyble says.

"Cooperation and especially food sharing are essential for survival in a hunting-and-gathering economy," Dyble says. "The proverb that 'it takes a village to raise a child' is certainly true for hunter-gatherers, who, without food sharing to mitigate the day-to-day shortfalls in foraging, could simply not survive."

Dyble says that they now intend to explore the structure of other types of social networks in the hunter-gatherer communities, such as cooperation in childcare, and their overlap with food sharing.

Source: Cell Press [July 21, 2016]

On the outskirts of Beijing, a small limestone mountain named Dragon Bone Hill rises above the surrounding sprawl. Along the northern side, a path leads up to some fenced-off caves that draw 150,000 visitors each year, from schoolchildren to grey-haired pensioners. It was here, in 1929, that researchers discovered a nearly complete ancient skull that they determined was roughly half a million years old. Dubbed Peking Man, it was among the earliest human remains ever uncovered, and it helped to convince many researchers that humanity first evolved in Asia.

Since then, the central importance of Peking Man has faded. Although modern dating methods put the fossil even earlier—at up to 780,000 years old—the specimen has been eclipsed by discoveries in Africa that have yielded much older remains of ancient human relatives. Such finds have cemented Africa's status as the cradle of humanity—the place from which modern humans and their predecessors spread around the globe—and relegated Asia to a kind of evolutionary cul-de-sac.

But the tale of Peking Man has haunted generations of Chinese researchers, who have struggled to understand its relationship to modern humans. "It's a story without an ending," says Wu Xinzhi, a palaeontologist at the Chinese Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing. They wonder whether the descendants of Peking Man and fellow members of the species Homo erectus died out or evolved into a more modern species, and whether they contributed to the gene pool of China today.

Keen to get to the bottom of its people's ancestry, China has in the past decade stepped up its efforts to uncover evidence of early humans across the country. It is reanalysing old fossil finds and pouring tens of millions of dollars a year into excavations. And the government is setting up a US$1.1-million laboratory at the IVPP to extract and sequence ancient DNA.

The investment comes at a time when palaeoanthropologists across the globe are starting to pay more attention to Asian fossils and how they relate to other early hominins—creatures that are more closely related to humans than to chimps. Finds in China and other parts of Asia have made it clear that a dazzling variety of Homo species once roamed the continent. And they are challenging conventional ideas about the evolutionary history of humanity.

"Many Western scientists tend to see Asian fossils and artefacts through the prism of what was happening in Africa and Europe," says Wu. Those other continents have historically drawn more attention in studies of human evolution because of the antiquity of fossil finds there, and because they are closer to major palaeoanthropology research institutions, he says. "But it's increasingly clear that many Asian materials cannot fit into the traditional narrative of human evolution."

Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, agrees. "Asia has been a forgotten continent," he says. "Its role in human evolution may have been largely under-appreciated."

Evolving story

In its typical form, the story of Homo sapiens starts in Africa. The exact details vary from one telling to another, but the key characters and events generally remain the same. And the title is always 'Out of Africa'.

In this standard view of human evolution, H. erectus first evolved there more than 2 million years ago. Then, some time before 600,000 years ago, it gave rise to a new species: Homo heidelbergensis, the oldest remains of which have been found in Ethiopia. About 400,000 years ago, some members of H. heidelbergensis left Africa and split into two branches: one ventured into the Middle East and Europe, where it evolved into Neanderthals; the other went east, where members became Denisovans—a group first discovered in Siberia in 2010. The remaining population of H. heidelbergensis in Africa eventually evolved into our own species, H. sapiens, about 200,000 years ago. Then these early humans expanded their range to Eurasia 60,000 years ago, where they replaced local hominins with a minuscule amount of interbreeding.

A hallmark of H. heidelbergensis—the potential common ancestor of Neanderthals, Denisovans and modern humans—is that individuals have a mixture of primitive and modern features. Like more archaic lineages, H. heidelbergensis has a massive brow ridge and no chin. But it also resembles H. sapiens, with its smaller teeth and bigger braincase. Most researchers have viewed H. heidelbergensis—or something similar—as a transitional form between H. erectus and H. sapiens.

Unfortunately, fossil evidence from this period, the dawn of the human race, is scarce and often ambiguous. It is the least understood episode in human evolution, says Russell Ciochon, a palaeoanthropologist at the University of Iowa in Iowa City. "But it's central to our understanding of humanity's ultimate origin."

The tale is further muddled by Chinese fossils analysed over the past four decades, which cast doubt over the linear progression from African H. erectus to modern humans. They show that, between roughly 900,000 and 125,000 years ago, east Asia was teeming with hominins endowed with features that would place them somewhere between H. erectus and H. sapiens, says Wu.

"Those fossils are a big mystery," says Ciochon. "They clearly represent more advanced species than H. erectus, but nobody knows what they are because they don't seem to fit into any categories we know."

The fossils' transitional characteristics have prompted researchers such as Stringer to lump them with H. heidelbergensis. Because the oldest of these forms, two skulls uncovered in Yunxian in Hubei province, date back 900,000 years >^{1, 2}>, Stringer even suggests that H. heidelbergensis might have originated in Asia and then spread to other continents.

But many researchers, including most Chinese palaeontologists, contend that the materials from China are different from European and African H. heidelbergensis fossils, despite some apparent similarities. One nearly complete skull unearthed at Dali in Shaanxi province and dated to 250,000 years ago, has a bigger braincase, a shorter face and a lower cheekbone than most H. heidelbergensis specimens>3, suggesting that the species was more advanced.

Such transitional forms persisted for hundreds of thousands of years in China, until species appeared with such modern traits that some researchers have classified them as H. sapiens. One of the most recent of these is represented by two teeth and a lower jawbone, dating to about 100,000 years ago, unearthed in 2007 by IVPP palaeoanthropologist Liu Wu and his colleagues>4. Discovered in Zhirendong, a cave in Guangxi province, the jaw has a classic modern-human appearance, but retains some archaic features of Peking Man, such as a more robust build and a less-protruding chin.

Most Chinese palaeontologists—and a few ardent supporters from the West—think that the transitional fossils are evidence that Peking Man was an ancestor of modern Asian people. In this model, known as multiregionalism or continuity with hybridization, hominins descended from H. erectus in Asia interbred with incoming groups from Africa and other parts of Eurasia, and their progeny gave rise to the ancestors of modern east Asians, says Wu.

Support for this idea also comes from artefacts in China. In Europe and Africa, stone tools changed markedly over time, but hominins in China used the same type of simple stone instruments from about 1.7 million years ago to 10,000 years ago. According to Gao Xing, an archaeologist at the IVPP, this suggests that local hominins evolved continuously, with little influence from outside populations.

Politics at play?

Some Western researchers suggest that there is a hint of nationalism in Chinese palaeontologists' support for continuity. "The Chinese—they do not accept the idea that H. sapiens evolved in Africa," says one researcher. "They want everything to come from China."

Chinese researchers reject such allegations. "This has nothing to do with nationalism," says Wu. It's all about the evidence—the transitional fossils and archaeological artefacts, he says. "Everything points to continuous evolution in China from H. erectus to modern human."

But the continuity-with-hybridization model is countered by overwhelming genetic data that point to Africa as the wellspring of modern humans. Studies of Chinese populations show that 97.4% of their genetic make-up is from ancestral modern humans from Africa, with the rest coming from extinct forms such as Neanderthals and Denisovans>5. "If there had been significant contributions from Chinese H. erectus, they would show up in the genetic data," says Li Hui, a population geneticist at Fudan University in Shanghai. Wu counters that the genetic contribution from archaic hominins in China could have been missed because no DNA has yet been recovered from them.

Many researchers say that there are ways to explain the existing Asian fossils without resorting to continuity with hybridization. The Zhirendong hominins, for instance, could represent an exodus of early modern humans from Africa between 120,000 and 80,000 years ago. Instead of remaining in the Levant in the Middle East, as was thought previously, these people could have expanded into east Asia, says Michael Petraglia, an archaeologist at the University of Oxford, UK.

Other evidence backs up this hypothesis: excavations at a cave in Daoxian in China's Hunan province have yielded 47 fossil teeth so modern-looking that they could have come from the mouths of people today. But the fossils are at least 80,000 years old, and perhaps 120,000 years old, Liu and his colleagues reported last year>6. "Those early migrants may have interbred with archaic populations along the way or in Asia, which could explain Zhirendong people's primitive traits," says Petraglia.

Another possibility is that some of the Chinese fossils, including the Dali skull, represent the mysterious Denisovans, a species identified from Siberian fossils that are more than 40,000 years old. Palaeontologists don't know what the Denisovans looked like, but studies of DNA recovered from their teeth and bones indicate that this ancient population contributed to the genomes of modern humans, especially Australian Aborigines, Papua New Guineans and Polynesians—suggesting that Denisovans might have roamed Asia.

Maria Martinon-Torres, a palaeoanthropologist at University College London, is among those who proposed that some of the Chinese hominins were Denisovans. She worked with IVPP researchers on an analysis>7, published last year, of a fossil assemblage uncovered at Xujiayao in Hebei province—including partial jaws and nine teeth dated to 125,000–100,000 years ago. The molar teeth are massive, with very robust roots and complex grooves, reminiscent of those from Denisovans, she says.

A third idea is even more radical. It emerged when Martinon-Torres and her colleagues compared more than 5,000 fossil teeth from around the world: the team found that Eurasian specimens are more similar to each other than to African ones>8. That work and more recent interpretations of fossil skulls suggest that Eurasian hominins evolved separately from African ones for a long stretch of time. The researchers propose that the first hominins that left Africa 1.8 million years ago were the eventual source of modern humans. Their descendants mostly settled in the Middle East, where the climate was favourable, and then produced waves of transitional hominins that spread elsewhere. One Eurasian group went to Indonesia, another gave rise to Neanderthals and Denisovans, and a third ventured back into Africa and evolved into H. sapiens, which later spread throughout the world. In this model, modern humans evolved in Africa, but their immediate ancestor originated in the Middle East.

Not everybody is convinced. "Fossil interpretations are notoriously problematic," says Svante Paabo, a palaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. But DNA from Eurasian fossils dating to the start of the human race could help to reveal which story—or combination—is correct. China is now making a push in that direction. Qiaomei Fu, a palaeogeneticist who did her PhD with Paabo, returned home last year to establish a lab to extract and sequence ancient DNA at the IVPP. One of her immediate goals is to see whether some of the Chinese fossils belong to the mysterious Denisovan group. The prominent molar teeth from Xujiayao will be an early target. "I think we have a prime suspect here," she says.

Fuzzy picture

Despite the different interpretations of the Chinese fossil record, everybody agrees that the evolutionary tale in Asia is much more interesting than people appreciated before. But the details remain fuzzy, because so few researchers have excavated in Asia.

When they have, the results have been startling. In 2003, a dig on Flores island in Indonesia turned up a diminutive hominin>9, which researchers named Homo floresiensis and dubbed the hobbit. With its odd assortment of features, the creature still provokes debate about whether it is a dwarfed form of H. erectus or some more primitive lineage that made it all the way from Africa to southeast Asia and lived until as recently as 60,000 years ago. Last month, more surprises emerged from Flores, where researchers found the remains of a hobbit-like hominin in rocks about 700,000 years old>10.

Recovering more fossils from all parts of Asia will clearly help to fill in the gaps. Many palaeoanthropologists also call for better access to existing materials. Most Chinese fossils—including some of the finest specimens, such as the Yunxian and Dali skulls—are accessible only to a handful of Chinese palaeontologists and their collaborators. "To make them available for general studies, with replicas or CT scans, would be fantastic," says Stringer. Moreover, fossil sites should be dated much more rigorously, preferably by multiple methods, researchers say.

But all agree that Asia—the largest continent on Earth—has a lot more to offer in terms of unravelling the human story. "The centre of gravity," says Petraglia, "is shifting eastward."

Author: Jane Qiu | Source: Nature 535, 22–25 (14 July 2016) doi:10.1038/535218a [July 15, 2016]

In a remarkable technical feat, researchers have sequenced DNA from fossils in Spain that are about 300,000 to 400,000 years old and have found an ancestor—or close relative—of Neanderthals. The nuclear DNA, which is the oldest ever sequenced from a member of the human family, may push back the date for the origins of the distinct ancestors of Neanderthals and modern humans, according to a presentation here yesterday at the fifth annual meeting of the European Society for the study of human evolution.

Ever since researchers first discovered thousands of bones and teeth from 28 individuals in the mid-1990s from Sima de los Huesos (“pit of bones”), a cave in the Atapuerca Mountains of Spain, they had noted that the fossils looked a lot like primitive Neanderthals. The Sima people, who lived before Neanderthals, were thought to have emerged in Europe. Yet their teeth, jaws, and large nasal cavities were among the traits that closely resembled those of Neanderthals, according to a team led by paleontologist Juan-Luis Arsuaga of the Complutense University of Madrid. As a result, his team classified the fossils as members of Homo heidelbergensis, a species that lived about 600,000 to 250,000 years ago in Europe, Africa, and Asia. Many researchers have thought H. heidelbergensis gave rise to Neanderthals and perhaps also to our species, H. sapiens, in the past 400,000 years or so.

But in 2013, the Sima fossils’ identity suddenly became complicated when a study of the maternally inherited mitochondrial DNA (mtDNA) from one of the bones revealed that it did not resemble that of a Neanderthal. Instead, it more closely matched the mtDNA of a Denisovan, an elusive type of extinct human discovered when its DNA was sequenced from a finger bone from Denisova Cave in Siberia. That finding was puzzling, prompting researchers to speculate that perhaps the Sima fossils had interbred with very early Denisovans or that the “Denisovan” mtDNA was the signature of an even more ancient hominin lineage, such as H. erectus. At the time, researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who had obtained the mtDNA announced that they would try to sequence the nuclear DNA of the fossils to solve the mystery.

After 2 years of intense effort, paleogeneticist Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology has finally sequenced enough nuclear DNA from fossils of a tooth and a leg bone from the pit to solve the mystery. The task was especially challenging because the ancient DNA was degraded to short fragments, made up of as few as 25 to 40 single nucleotides. (Nucleotides—also known as base pairs—are the building blocks of DNA.) Although he and his colleagues did not sequence the entire genomes of the fossils, Meyer reported at the meeting that they did get 1 million to 2 million base pairs of ancient nuclear DNA.

They scanned this DNA for unique markers found only in Neanderthals or Denisovans or modern humans, and found that the two Sima fossils shared far more alleles—different nucleotides at the same address in the genome—with Neanderthals than Denisovans or modern humans. “Indeed, the Sima de los Huesos specimens are early Neanderthals or related to early Neanderthals,” suggesting that the split of Denisovans and Neanderthals should be moved back in time, Meyer reported at the meeting.

Researchers at the meeting were impressed by this new breakthrough in ancient DNA research. “This has been the next frontier with ancient DNA,” says evolutionary biologist Greger Larson of the University of Oxford in the United Kingdom.

The close affinity with Neanderthals, but not with Denisovans or modern humans, suggests that the lineage leading to Neanderthals was separate from other archaic humans earlier than most researchers have thought. That means that the ancestors of modern humans also had to split earlier than expected from the population that gave rise to Neanderthals and Denisovans, who were more closely related to each other than they were to modern humans. (Although all three groups interbred at low levels after their evolutionary paths diverged—and such interbreeding may have been the source of the Denisovan mtDNA in the first Sima fossil whose DNA was sequenced.) Indeed, Meyer suggested in his talk that the ancestors of H. sapiens may have diverged from the branch leading to Neanderthals and Denisovans as early as 550,000 to 765,000 years ago, although those results depend on different mutation rates in humans and are still unpublished.

That would mean that the ancestors of humans were already wandering down a solitary path apart from the other kinds of archaic humans on the planet 100,000 to 400,000 years earlier than expected. “It resolves one controversy—that they’re in the Neanderthal clade,” says paleoanthropologist Chris Stringer of the Natural History Museum in London. “But it’s not all good news: From my point of view, it pushes back the origin of H. sapiens from the Neanderthals and Denisovans.” The possibility that humans were a distinct group so early shakes up the human family tree, promising to lead to new debate about when and where the branches belong.

Author: Ann Gibbons | Source: ScienceMag/AAAS [September 11, 2015]