What makes the human brain distinct from that of all other animals -- including even our closest primate relatives? In an analysis of cell types in the prefrontal cortex of four primate species, Yale researchers identified species-specific -- particularly human-specific -- features, they report Aug. 25 in the journal Science.
And they found that what makes us human may also makes us susceptible to neuropsychiatric diseases.
For the study, the researchers looked specifically at the dorsolateral prefrontal cortex (dlPFC), a brain region that is unique to primates and essential for higher-order cognition. Using a single cell RNA-sequencing technique, they profiled expression levels of genes in hundreds of thousands of cells collected from the dlPFC of adult humans, chimpanzees, macaque, and marmoset monkeys.
"Today, we view the dorsolateral prefrontal cortex as the core component of human identity, but still we don't know what makes this unique in humans and distinguishes us from other primate species." said Nenad Sestan, the Harvey and Kate Cushing Professor of Neuroscience at Yale, professor of comparative medicine, of genetics. and of psychiatry, and the lead senior author of the paper. "Now we have more clues."
To answer this, the researchers first asked whether there are there any cell types uniquely present in humans or other analyzed non-human primate species. After grouping cells with similar expression profiles they revealed 109 shared primate cell types but also five that were not common to all species. These included a type of microglia, or brain-specific immune cell, that was present only in humans and a second type shared by only humans and chimpanzees.
The human-specific microglia type exists throughout development and adulthood, the researchers found, suggesting the cells play a role in maintenance of the brain upkeep rather than combatting disease.
"We humans live in a very different environment with a unique lifestyle compared to other primate species; and glia cells, including microglia, are very sensitive to these differences," Sestan said. "The type of microglia found in the human brain might represent an immune response to the environment."
An analysis of gene expression in the microglia revealed another human-specific surprise -- the presence of the gene FOXP2. This discovery raised great interest because variants of FOXP2 have been linked to verbal dyspraxia, a condition in which patients have difficulty producing language or speech. Other studies have also shown that FOXP2 is associated with other neuropsychiatric diseases, such as autism, schizophrenia, and epilepsy.
Sestan and colleagues found that this gene exhibits primate-specific expression in a subset of excitatory neurons and human-specific expression in microglia.
"FOXP2 has intrigued many scientists for decades, but still we had no idea of what makes it unique in humans versus other primate species," said Shaojie Ma, a postdoctoral associate in Sestan's lab and co-lead author. We are extremely excited about the FOXP2 findings because they open new directions in the study of language and diseases."
The acquisition of bipedalism is considered to be a decisive step in human evolution. Nevertheless, there is no consensus on its modalities and age, notably due to the lack of fossil remains. A research team, involving researchers from the CNRS, the University of Poitiers1 and their Chadian partners, examined three limb bones from the oldest human representative currently identified, Sahelanthropus tchadensis. Published in Nature on August 24, 2022, this study reinforces the idea of bipedalism being acquired very early in our history, at a time still associated with the ability to move on four limbs in trees.
At 7 million years old, Sahelanthropus tchadensis is considered the oldest representative species of humanity. Its description dates back to 2001 when the Franco-Chadian Paleoanthropological Mission (MPFT) discovered the remains of several individuals at Toros-Menalla in the Djurab Desert (Chad), including a very well-preserved cranium. This cranium, and in particular the orientation and anterior position of the occipital foramen where the vertebral column is inserted, indicates a mode of locomotion on two legs, suggesting that it was capable of bipedalism2.
In addition to the cranium, nicknamed Toumaï, and fragments of jaws and teeth that have already been published, the locality of Toros-Menalla 266 (TM 266) yielded two ulnae (forearm bone) and a femur (thigh bone). These bones were also attributed to Sahelanthropus because no other large primate was found at the site; however, it is impossible to know if they belong to the same individual as the cranium. Palaeontologists from the University of Poitiers, the CNRS, the University of N'Djamena and the National Centre of Research for Development (CNRD, Chad) published their complete analysis in Nature on August 24, 2022.
The femur and ulnae were subjected to a battery of measurements and analyses, concerning both their external morphology, and their internal structures using microtomography imaging: biometric measurements, geometric morphometrics, biomechanical indicators, etc. These data were compared to those of a relatively large sample of extant and fossil apes: chimpanzees, gorillas, orangutans, Miocene apes, and members of the human group (Orrorin, Ardipithecus, australopithecines, ancient Homo, Homo sapiens).
The structure of the femur indicates that Sahelanthropus was usually bipedal on the ground, but probably also in trees. According to results from the ulnae, this bipedalism coexisted in arboreal environments with a form of quadrupedalism, that is arboreal clambering enabled by firm hand grips, clearly differing from that of gorillas and chimpanzees who lean on the back of their phalanges.
The conclusions of this study, including the identification of habitual bipedalism, are based on the observation and comparison of more than twenty characteristics of the femur and ulnae. They are, by far, the most parsimonious interpretation of the combination of these traits. All these data reinforce the concept of a very early bipedal locomotion in human history, even if at this stage other modes of locomotion were also practiced.
If you've ever suffered from a sore jaw that popped or clicked when you chewed gum or crunched hard foods, you may be able to blame it on your extinct ancestors.
That's according to a Duke University-led study of the chewing mechanics of an ancient human relative called Homo floresiensis, which inhabited the Indonesian island of Flores before our species arrived there some 50,000 years ago.
Not much more than three feet tall, the hominin's diminutive size earned it the nickname "the Hobbit," after the characters in J.R.R. Tolkien's "The Lord of the Rings." For the new study, which was published Aug. 13 in the journal Interface Focus, the researchers wanted to understand how the Hobbit's skull behaved while it ate its food.
However, thousands of years of fossilization had left its skull -- the only one that has been found so far -- damaged and misshapen. Before the researchers could test it out, they had to restore it as close to its original shape as possible. Collaborators at Italy's University of Bologna created a 3D virtual model, built from X-ray CT scans, digitally filling in the missing pieces to reconstruct what the skull of Homo floresiensis might have looked like when it roamed the island some 100,000 to 60,000 years ago.
From that, they used computer simulations and a technique called finite element analysis to give the virtual skull characteristics that mimic the real thing, such as the stiffness of the bones and the pulling action of the muscles. Then they had the virtual skull chomp down with its back teeth -- premolars and molars -- and analyzed the forces at work with each bite, essentially subjecting it to a digital crash test.
The researchers mapped the strains within their digital model of the Hobbit's facial bones during biting, comparing the results to similar simulations for earlier human relatives called australopiths that lived some two to three million years ago in Africa, along with chimpanzees and humans living today.
The team determined that the Hobbit's bite could have exerted around 1300 Newtons of force, comparable to the chomping power of modern humans and several of our extinct cousins. But had it bitten down too vigorously on a hard nut or a tough hunk of meat, the findings suggest Homo floresiensis would have been at greater risk than our earlier human kin of straining its facial bones, or dislocating the joint where the lower and upper jaws meet.
"We don't really know what Homo floresiensis ate," said first author Rebecca Cook, a doctoral student in evolutionary anthropology at Duke. Patterns of wear on the teeth, combined with pygmy elephant bones and other animal remains unearthed from the same cave where the Hobbit was found suggest that it ate at least some meat.
But the results suggest that exceedingly hard or tough foods, which would have been no problem for an australopith to gnaw on or crack open, might have given the Hobbit a TMJ headache.
"Similar patterns are observed in modern humans," Cook said.
Millions of years of human evolution gave us smaller teeth and more lightweight skulls, because cooking our food and slicing and pounding it with stone tools, and probably also eating meat, made having overbuilt skulls unnecessary.
But years after the Hobbit's discovery its facial features remain a puzzle. Its skull had a curious mix of traits, some of which -- like its heavyset lower jaw -- are similar to our earlier and more ape-like ancestors, while others -- like its small delicate face -- resemble humans today.
"This can make it confusing as to where this species falls on the family tree of hominin evolutionary relationships," Cook said.
The new study suggests this shift to smaller faces, weaker bites and achey jaws evolved early, before the common ancestors of Homo floresiensis and modern humans went their separate ways.
Justin Ledogar, Duke researcher and senior author of the study, says the next step is to do similar analyses on earlier members of the genus Homo, including Homo erectus. The first known hominin to use fire and cook food, this species also had smaller teeth, jaws and faces than earlier hominins, and is thought by some to be the ancestor of Homo floresiensis.
The researchers say the work could help answer lingering questions about where Homo floresiensis came from, how it lived and how it fits into the human evolutionary tree.
A near-perfectly preserved ancient human fossil known as the Harbin cranium sits in the Geoscience Museum in Hebei GEO University. The largest of known Homo skulls, scientists now say this skull represents a newly discovered human species named Homo longi or "Dragon Man." Their findings, appearing in three papers publishing June 25 in the journal The Innovation, suggest that the Homo longi lineage may be our closest relatives -- and has the potential to reshape our understanding of human evolution.
"The Harbin fossil is one of the most complete human cranial fossils in the world," says author Qiang Ji, a professor of paleontology of Hebei GEO University. "This fossil preserved many morphological details that are critical for understanding the evolution of the Homo genus and the origin of Homo sapiens."
The cranium was reportedly discovered in the 1930s in Harbin City of the Heilongjiang province of China. The massive skull could hold a brain comparable in size to modern humans' but had larger, almost square eye sockets, thick brow ridges, a wide mouth, and oversized teeth. "While it shows typical archaic human features, the Harbin cranium presents a mosaic combination of primitive and derived characters setting itself apart from all the other previously-named Homo species," says Ji, leading to its new species designation of Homo longi.
Scientists believe the cranium came from a male individual, approximately 50 years old, living in a forested, floodplain environment as part of a small community. "Like Homo sapiens, they hunted mammals and birds, and gathered fruits and vegetables, and perhaps even caught fish," remarks author Xijun Ni, a professor of primatology and paleoanthropology at the Chinese Academy of Sciences and Hebei GEO University. Given that the Harbin individual was likely very large in size as well as the location where the skull was found, researchers suggest H. longi may have been adapted for harsh environments, allowing them to disperse throughout Asia.
Using a series of geochemical analyses, Ji, Ni, and their team dated the Harbin fossil to at least 146,000 years, placing it in the Middle Pleistocene, a dynamic era of human species migration. They hypothesize that H. longi and H. sapiens could have encountered each other during this era.
"We see multiple evolutionary lineages of Homo species and populations co-existing in Asia, Africa, and Europe during that time. So, if Homo sapiens indeed got to East Asia that early, they could have a chance to interact with H. longi, and since we don't know when the Harbin group disappeared, there could have been later encounters as well," says author Chris Stringer, a paleoanthropologist at the Nature History Museum in London.
Looking farther back in time, the researchers also find that Homo longi is one of our closest hominin relatives, even more closely related to us than Neanderthals. "It is widely believed that the Neanderthal belongs to an extinct lineage that is the closest relative of our own species. However, our discovery suggests that the new lineage we identified that includes Homo longi is the actual sister group of H. sapiens," says Ni.
Their reconstruction of the human tree of life also suggests that the common ancestor we share with Neanderthals existed even further back in time. "The divergence time between H. sapiens and the Neanderthals may be even deeper in evolutionary history than generally believed, over one million years," says Ni. If true, we likely diverged from Neanderthals roughly 400,000 years earlier than scientists had thought.
If you could travel back in time to 100,000 years ago, you'd find yourself living among several different groups of humans, including Modern Humans (those anatomically similar to us), Neanderthals, and Denisovans. We know quite a bit about Neanderthals, thanks to numerous remains found across Europe and Asia. But exactly what our Denisovan relatives might have looked like had been anyone's guess for a simple reason: the entire collection of Denisovan remains includes three teeth, a pinky bone and a lower jaw. Now, as reported in the scientific journal Cell, a team led by Hebrew University of Jerusalem (HUJI) researchers Professor Liran Carmel and Dr. David Gokhman (currently a postdoc at Stanford) has produced reconstructions of these long-lost relatives based on patterns of methylation (chemical changes) in their ancient DNA.
"We provide the first reconstruction of the skeletal anatomy of Denisovans," says lead author Carmel of HUJI's Institute of Life Sciences. "In many ways, Denisovans resembled Neanderthals but in some traits they resembled us and in others they were unique."
Denisovan remains were first discovered in 2008 and have fascinated human evolution researchers ever since. They lived in Siberia and Eastern Asia, and went extinct approximately 50,000 years ago. We don't yet know why. That said, up to 6% of present-day Melanesians and Aboriginal Australians contain Denisovan DNA. Further, Denisovan DNA likely contributed to modern Tibetans' ability to live in high altitudes and to Inuits' ability to withstand freezing temperatures.
Overall, Carmel and his team identified 56 anatomical features in which Denisovans differ from modern humans and/or Neanderthals, 34 of them in the skull. For example, the Denisovan's skull was probably wider than that of modern humans' or Neanderthals'. They likely also had a longer dental arch and no chin.
The researchers came to these conclusions after three years of intense work studying DNA methylation maps. DNA methylation refers to chemical modifications that affect a gene's activity but not its underlying DNA sequence. The researchers first compared DNA methylation patterns among the three human groups to find regions in the genome that were differentially methylated. Next, they looked for evidence about what those differences might mean for anatomical features -- based on what's known about human disorders in which those same genes lose their function.
"In doing so, we got a prediction as to what skeletal parts are affected by differential regulation of each gene and in what direction that skeletal part would change -- for example, a longer or shorter femur bone," Dr. Gokhman explained.
To test this ground-breaking method, the researchers applied it to two species whose anatomy is known: the Neanderthal and the chimpanzee. They found that roughly 85% of their trait reconstructions were accurate in predicting which traits diverged and in which direction they diverged. Then, they applied this method to the Denisovan and were able to produce the first reconstructed anatomical profile of the mysterious Denisovan.
As for the accuracy of their Denisovan profile, Carmel shared, "One of the most exciting moments happened a few weeks after we sent our paper to peer-review. Scientists had discovered a Denisovan jawbone! We quickly compared this bone to our predictions and found that it matched perfectly. Without even planning on it, we received independent confirmation of our ability to reconstruct whole anatomical profiles using DNA that we extracted from a single fingertip."
In their Cell paper, Carmel and his colleagues predict many Denisovan traits that resemble Neanderthals', such as a sloping forehead, long face and large pelvis, and others that are unique among humans, for example, a large dental arch and very wide skull. Do these traits shed light on the Denisovan lifestyle? Could they explain how Denisovans survived the extreme cold of Siberia?
Virtual rendering of the brain endocast of "Little Foot". Photo of the original skull by M. Lotter and R.J. Clarke.
First ever endocast reconstruction of the nearly complete brain of the hominin known as Little Foot reveals a small brain combining ape-like and human-like features.
MicroCT scans of the Australopithecus fossil known as Little Foot shows that the brain of this ancient human relative was small and shows features that are similar to our own brain and others that are closer to our ancestor shared with living chimpanzees.
While the brain features structures similar to modern humans -- such as an asymmetrical structure and pattern of middle meningeal vessels -- some of its critical areas such as an expanded visual cortex and reduced parietal association cortex points to a condition that is distinct from us.
The Australopithecus fossil named Little Foot, an ancient human relative, was excavated over 14 years from the Sterkfontein Caves in South Africa, by Professor Ronald Clarke, from the University of the Witwatersrand (Wits). Its brain endocast was virtually extracted, described and analysed by Wits researcher, Dr Amélie Beaudet, and the Sterkfontein team by using MicroCT scans of the fossil.
The scans reveal impressions left on the skull by the brain and the vessels that feed it, along with the shape of the brain. Beaudet's research was released as the first in a series of papers planned for a special issue of this journal on the near-complete "Little Foot" skeleton in the Journal of Human Evolution.
"Our ability to reconstruct features of early hominin brains has been limited by the very fragmentary nature of the fossil record. The Little Foot endocast is exceptionally well preserved and relatively complete, allowing us to explore our own origins better than ever before," says Beaudet.
The endocast showed that Little Foot's brain was asymmetrical, with a distinct left occipital petalia. Brain asymmetry is essential for lateralisation of brain function. Asymmetry occurs in humans and living apes, as well as in other younger hominin endocasts. Little Foot now shows us that this brain asymmetry was present at a very early date (from 3.67 million years ago), and supports suggestions that it was probably present in the last common ancestor of hominins and other great apes.
Other brain structures, such as an expanded visual cortex, suggests that the brain of Little Foot probably had some features that are closer to the ancestor we share with living chimpanzees.
"In human evolution, when know that a reduced visual cortex, as we can see in our own brain, is related to a more expanded parietal cortex -- which is a critical cerebral area responsible for several aspects of sensory processing and sensorimotor integration," says Beaudet. "On the contrary, Little Foot has a large visual cortex, which is more similar to chimpanzees than to humans."
Beaudet and her colleagues compared the Little Foot endocast with endocasts of 10 other South African hominins dating between three and 1.5 million years ago. Their preliminary calculation of Little Foot's endocranial volume was found to be at the low end of the range for Australopithecus, which is in keeping with its great age and its place among other very early fossils of Australopithecus from East Africa.
The study also has shown that the vascular system in Australopithecus was more complex than previously thought, which raises new questions on the metabolism of the brain at this time. This might be consistent with a previous hypothesis suggesting that the endocranial vascular system in Australopithecus was closer to modern humans than it was in the geologically younger Paranthropus genus.
"This would mean that even if Little Foot's brain was different from us, the vascular system that allows for blood flow (which brings oxygen) and may control temperature in the brain -- both essential aspects for evolving a large and complex brain -- were possibly already present at that time," says Beaudet.
Given its geological age of over 3 million years, Little Foot's brain suggests that younger hominins evolved greater complexity in certain brain structures over time, perhaps in response to increasing environmental pressures experienced after 2.6 million years ago with continuing reduction in closed habitats.
Map of the potential distribution of archaic hominins, including H.
erectus, H. floresiensis, H. neanderthalenesis, Denisovans and archaic
African hominins, in the Old World at the time of the evolution and
dispersal of H. sapiens between approximately 300 and 60 thousand years
ago.
Critical review of growing archaeological and palaeoenvironmental datasets relating to the Middle and Late Pleistocene (300-12 thousand years ago) hominin dispersals within and beyond Africa, published today in Nature Human Behaviour, demonstrates unique environmental settings and adaptations for Homo sapiens relative to previous and coexisting hominins such as Homo neanderthalensis and Homo erectus. Our species' ability to occupy diverse and 'extreme' settings around the world stands in stark contrast to the ecological adaptations of other hominin taxa, and may explain how our species became the last surviving hominin on the planet.
The paper, by scientists from the Max Planck Institute for the Science of Human History and the University of Michigan suggests investigations into what it means to be human should shift from attempts to uncover the earliest material traces of 'art', 'language', or technological 'complexity' towards understanding what makes our species ecologically unique. In contrast to our ancestors and contemporary relatives, our species not only colonized a diversity of challenging environments, including deserts, tropical rainforests, high altitude settings, and the palaeoarctic, but also specialized in its adaptation to some of these extremes.
Ancestral ecologies -- the ecology of Early and Middle Pleistocene Homo
Although all hominins that make up the genus Homo are often termed 'human' in academic and public circles, this evolutionary group, which emerged in Africa around 3 million years ago, is highly diverse. Some members of the genus Homo (namely Homo erectus) had made it to Spain, Georgia, China, and Indonesia by 1 million years ago. Yet, existing information from fossil animals, ancient plants, and chemical methods all suggest that these groups followed and exploited environmental mosaics of forest and grassland. It has been argued that Homo erectus and the 'Hobbit', or Homo floresiensis, used humid, resource-scarce tropical rainforest habitats in Southeast Asia from 1 million years ago to 100,000 and 50,000 years ago, respectively. However, the authors found no reliable evidence for this.
It has also been argued that our closest hominin relatives, Homo Neanderthalensis - or the Neanderthals -- were specialized to the occupation of high latitude Eurasia between 250,000 and 40,000 years ago. The base for this includes a face shape potentially adapted to cold temperatures and a hunting focus on large animals such as woolly mammoths. Nevertheless, a review of the evidence led the authors to again conclude that Neanderthals primarily exploited a diversity of forest and grassland habitats, and hunted a diversity of animas, from temperature northern Eurasia to the Mediterranean.
Deserts, rainforests, mountains, and the arctic
In contrast to these other members of the genus Homo, our species -- Homo sapiens - had expanded to higher-elevation niches than its hominin predecessors and contemporaries by 80-50,000 years ago, and by at least 45,000 years ago was rapidly colonizing a range of palaeoarctic settings and tropical rainforest conditions across Asia, Melanesia, and the Americas. Furthermore, the authors argue that the continued accumulation of better-dated, higher resolution environmental datasets associated with our species' crossing the deserts of northern Africa, the Arabian Peninsula, and northwest India, as well as the high elevations of Tibet and the Andes, will further help to determine the degree to which our species demonstrated novel colonizing capacities in entering these regions.
Finding the origins of this ecological 'plasticity', or the ability to occupy a number of very different environments, currently remains difficult in Africa, particularly back towards the evolutionary origins of Homo sapiens 300-200,000 years ago. However, the authors argue that there are tantalizing hints for novel environmental contexts of human habitation and associated technological shifts across Africa just after this timeframe. They hypothesize that the drivers of these changes will become more apparent with future work, especially that which tightly integrates archaeological evidence with highly resolved local palaeoecological data. For example, lead author of the paper, Dr. Patrick Roberts, suggests, "although a focus on finding new fossils or genetic characterization of our species and its ancestors has helped rough out the broad timing and location of hominin specifications, such efforts are largely silent on the various environmental contexts of biocultural selection."
The 'generalist specialist' -- a very sapiens niche
One of the main new claims of the authors is that the evidence for human occupation of a huge diversity of environmental settings across the majority of the Earth's continents by the Late Pleistocene hints at a new ecological niche, that of the 'generalist specialist'. As Roberts states "A traditional ecological dichotomy exists between 'generalists', who can make use of a variety of different resources and inhabit a variety of environmental conditions, and 'specialists', who have a limited diet and narrow environmental tolerance. However, Homo sapiens furnish evidence for 'specialist' populations, such as mountain rainforest foragers or palaeoarctic mammoth hunters, existing within what is traditionally defined as a 'generalist' species."
This ecological ability may have been aided by extensive cooperation between non-kin individuals among Pleistocene Homo sapiens, argues Dr. Brian Stewart, co-author of the study. "Non-kin food sharing, long-distance exchange, and ritual relationships would have allowed populations to 'reflexively' adapt to local climatic and environmental fluctuations, and outcompete and replace other hominin species." In essence, accumulating, drawing from, and passing down a large pool of cumulative cultural knowledge, in material or idea form, may have been crucial in the creation and maintenance of the generalist-specialist niche by our species in the Pleistocene. Implications for our pursuit of ancient humanity
The authors are clear that this proposition remains hypothetical and could be disproven by evidence for the use of 'extreme' environments by other members of the genus Homo. However, testing the 'generalist specialist' niche in our species encourages research in more extreme environments that have previously been neglected as unpromising for palaeoanthropological and archaeological work, including the Gobi Desert and Amazon rainforest. The expansion of such research is particularly important in Africa, the evolutionary cradle of Homo sapiens, where more detailed archaeological and environmental records dating back to 300-200,000 years ago are becoming increasingly crucial if we are to track the ecological abilities of the earliest humans.
It is also clear that growing evidence for hominin interbreeding and a complex anatomical and behavioural origin of our species in Africa highlights that archaeologists and palaeoanthropologists should focus on looking at the environmental associations of fossils. "While we often get excited by the discovery of new fossils or genomes, perhaps we need to think about the behavioural implications of these discoveries in more detail, and pay more attention to what these new finds tell us about new the passing of ecological thresholds" says Stewart. Work focusing on how the genetics of different hominins may have led to ecological and physical benefits such as high-altitude capacities or UV tolerance remain highly fruitful ways forward in this regard.
This is the 3.32 million-year-old Australopithecus afarensis foot from
Dikika, Ethiopia, superimposed over a footprint from a human toddler.
More than 3 million years ago, our ancient human ancestors, including their toddler-aged children, were standing on two feet and walking upright, according to a new study published in Science Advances.
"For the first time, we have an amazing window into what walking was like for a 2½-year-old, more than 3 million years ago," says lead author, Jeremy DeSilva, an associate professor of anthropology at Dartmouth College, who is one of the world's foremost authorities on the feet of our earliest ancestors. "This is the most complete foot of an ancient juvenile ever discovered."
The tiny foot, about the size of a human thumb, is part of a nearly complete 3.32-million-year-old skeleton of a young female Australopithecus afarensis discovered in 2002 in the Dikika region of Ethiopia by Zeresenay (Zeray) Alemseged, a professor of organismal biology and anatomy at the University of Chicago and senior author of the study. Alemseged is internationally known as a leading paleontologist on the study of human origins and human evolution.
"Placed at a critical time and the cusp of being human, Australopithecus afarensis was more derived than Ardipithecus (a facultative biped) but not yet an obligate strider like Homo erectus. The Dikika foot adds to the wealth of knowledge on the mosaic nature of hominin skeletal evolution" explained Alemseged.
Given that the fossil of the tiny foot is the same species as the famous Lucy fossil and was found in the same vicinity, it is not surprising that the Dikika child was erroneously labeled "Lucy's baby" by the popular press, though this youngster lived more than 200,000 years before Lucy.
In studying the fossil foot's remarkably preserved anatomy, the research team strived to reconstruct what life would have been like years ago for this toddler and how our ancestors survived. They examined what the foot would have been used for, how it developed and what it tells us about human evolution. The fossil record indicates that these ancient ancestors were quite good at walking on two legs. "Walking on two legs is a hallmark of being human. But, walking poorly in a landscape full of predators is a recipe for extinction," explained DeSilva.
Original picture (left) and virtual rendering of the Jacovec cranium
(middle) with two sections revealing the inner structure (right).
A cranium of a four-million-year-old fossil, that, in 1995 was described as the oldest evidence of human evolution in South Africa, has shown similarities to that of our own, when scanned through high resolution imaging systems.
The cranium of the extinct Australopithecus genus was found in the lower-lying deposits of the Jacovec Cavern in the Sterkfontein Caves, about 40km North-West of Johannesburg in South Africa. Dr Amelie Beaudet from the School of Geography, Archaeology and Environmental Studies of the University of the Witwatersrand and her colleagues from the Sterkfontein team scanned the cranium at the Evolutionary Studies Institute, based at the University of the Witwatersrand, in 2016 and applied advanced imaging techniques in "virtual paleontology" to further explore the anatomy of the cranium. Their research was funded by the Centre of Excellence in Palaeosciences, the Claude Leon Foundation and the French Institute of South Africa and was published in the Journal of Human Evolution.
"The Jacovec cranium represents a unique opportunity to learn more about the biology and diversity of our ancestors and their relatives and, ultimately, about their evolution," says Beaudet. "Unfortunately, the cranium is highly fragmentary and not much could be said about the identity nor the anatomy of the Jacovec specimen before."
Through high resolution scanning, the researchers were able to quantitatively and non-invasively explore fine details of the inner anatomy of the Jacovec specimen and to report previously unknown information about the genus Australopithecus.
"Our study revealed that the cranium of the Jacovec specimen and of the Ausralopithecus specimens from Sterkfontein in general was thick and essentially composed of spongy bone," says Beaudet. "This large portion of spongy bone, also found in our own cranium, may indicate that blood flow in the brain of Australopithecus may have been comparable to us, and/or that the braincase had an important role in the protection of the evolving brain."
In comparing this cranium to that of another extinct group of our family tree, Paranthropus, that lived in South Africa along with the first humans less than two-million-years ago, their study revealed an intriguing and unexpected aspect of the cranial anatomy in this genus.
"We also found that the Paranthropus cranium was relatively thin and essentially composed of compact bone. This result is of particular interest, as it may suggest a different biology," says Beaudet.
Situated in the Cradle of humankind, a Unesco World Heritage Site, the South African paleontological sites have played a pivotal role in the exploration of our origins. In particular, the Sterkfontein Caves site has been one of the most prolific fossil localities in Africa, with over 800 hominin remains representing 3 genera of hominin recovered since 1936, including the first adult Australopithecus, the iconic "Mrs Ples" and "Little Foot," the most complete single skeleton of an early hominin yet found.
This graphical abstract shows two waves of Denisovan ancestry have shaped present-day humans.
Modern humans co-existed and interbred not only with Neanderthals, but also with another species of archaic humans, the mysterious Denisovans. While developing a new genome-analysis method for comparing whole genomes between modern human and Denisovan populations, researchers unexpectedly discovered two distinct episodes of Denisovan genetic intermixing, or admixing, between the two. This suggests a more diverse genetic history than previously thought between the Denisovans and modern humans.
In a paper published in Cell on March 15, scientists at the University of Washington in Seattle determined that the genomes of two groups of modern humans with Denisovan ancestry -- individuals from Oceania and individuals from East Asia -- are uniquely different, indicating that there were two separate episodes of Denisovan admixture.
"What was known already was that Oceanian individuals, notably Papuan individuals, have significant amounts of Denisovan ancestry," says senior author Sharon Browning, a research professor of biostatistics, University of Washington School of Public Health. The genomes of modern Papuan individuals contain approximately 5% Denisovan ancestry."
Researchers also knew Denisovan ancestry is present to a lesser degree throughout Asia. The assumption was that the ancestry in Asia was achieved through migration, coming from Oceanian populations. "But in this new work with East Asians, we find a second set of Denisovan ancestry that we do not find in the South Asians and Papuans," she says. "This Denisovan ancestry in East Asians seems to be something they acquired themselves."
After studying more than 5,600 whole-genome sequences from individuals from Europe, Asia, America, and Oceania and comparing them to the Denisovan genome, Browning and colleagues determined that the Denisovan genome is more closely related to the modern East Asian population than to modern Papuans. "We analyzed all of the genomes searching for sections of DNA that looked like they came from Denisovans," says Browning, whose team relied on genomic information from the UK10K project, the 1000 Genomes Project, and the Simons Genome Diversity Project.
"When we compared pieces of DNA from the Papuans against the Denisovan genome, many sequences were similar enough to declare a match, but some of the DNA sequences in the East Asians, notably Han Chinese, Chinese Dai, and Japanese, were a much closer match with the Denisovan," she says.
What is known about Denisovan ancestry comes from a single set of archaic human fossils found in the Altai mountains in Siberia. That individual's genome was published in 2010, and other researchers quickly identified segments of Denisovan ancestry in several modern-day populations, most significantly with individuals from Oceania but also in East and South Asians.
"The assumption is that admixing with Denisovans occurred fairly quickly after humans moved out of Africa, around 50,000 years ago, but we do not know where in terms of location," Browning says. She theorizes that perhaps the ancestors of Oceanians admixed with a southern group of Denisovans while the ancestors of East Asians admixed with a northern group.
Femoral head bones of different species illustrating the size range in
the hominin lineage. From top to bottom: Australopithecus afarensis (4-3
million years; ~40 kg, 130 cm); Homo ergaster (1.9-1.4 million years;
55-60 kg; ~165 cm); Neanderthal (200.000-30.000 years; ~70 kg; ~163 cm).
A wide-ranging new study of fossils spanning over four million years suggests that stature and body mass advanced at different speeds during the evolution of hominins -- the ancestral lineage of which Homo sapiens alone still exist.
Published today in the journal Royal Society Open Science, the research also shows that, rather than steadily increasing in size, hominin bodies evolved in "pulse and stasis" fluctuations, with some lineages even shrinking.
The findings are from the largest study of hominin body sizes, involving 311 specimens dating from earliest upright species of 4.4m years ago right through to the modern humans that followed the last ice age.
While researchers describe the physical evolution of assorted hominin species as a "long and winding road with many branches and dead ends," they say that broad patterns in the data suggest bursts of growth at key stages, followed by plateaus where little changed for many millennia.
The scientists were surprised to find a "decoupling" of bulk and stature around one and a half million years ago, when hominins grew roughly 10cm taller but would not consistently gain any heft for a further million years, with an average increase of 10-15kgs occurring around 500,000 years ago.
Before this event, height and weight in hominin species appeared to evolve roughly "in concert," say the authors of this first study to jointly analyse both aspects of body size over millions of years.
"An increase solely in stature would have created a leaner physique, with long legs and narrow hips and shoulders. This may have been an adaptation to new environments and endurance hunting, as early Homo species left the forests and moved on to more arid African savannahs," says lead author Dr Manuel Will from Cambridge's Department of Archaeology, and a Research Fellow at Gonville and Caius College.
"The higher surface-to-volume ratio of a tall, slender body would be an advantage when stalking animals for hours in the dry heat, as a larger skin area increases the capacity for the evaporation of sweat."
"The later addition of body mass coincides with ever-increasing migrations into higher latitudes, where a bulkier body would be better suited for thermoregulation in colder Eurasian climates," he says.
However, Dr Will points out that, while these are valid theories, vast gaps in the fossil record continue to mask absolute truths. In fact, Will and colleagues often had to estimate body sizes from highly fragmented remains -- in some cases from just a single toe bone.
The study found body size to be highly variable during earlier hominin history, with a range of differently shaped species: from broad, gorilla-like Paranthropus to the more wiry or 'gracile' Australopithecus afarensis. Hominins from four million years ago weighed a rough average of 25kg and stood at 125-130cm.
As physicality morphs over deep time, increasingly converging on larger body sizes, the scientists observe three key "pulses" of significant change.
The first occurs with the dawn of our own defined species bracket, Homo, around 2.2-1.9m years ago. This period sees a joint surge in both height (around 20 cm) and weight (between 15-20kg).
Stature then separated from heft with a height increase alone of 10cm between 1.4-1.6m years ago, shortly after the emergence of Homo erectus. "From a modern perspective this is where we see a familiar stature reached and maintained. Body mass, however, is still some way off," explains Will.
It's not until a million years later (0.5-0.4m years ago) that consistently heavier hominins appear in the fossil record, with an estimated 10-15kg greater body mass signalling adaptation to environments north of the Mediterranean.
"From then onwards, average body height and weight stays more or less the same in the hominin lineage, leading ultimately to ourselves," says Will.
There are, however, a couple of exceptions to this grand narrative: Homo naledi and Homo floresiensis*. Recently discovered remains suggest these species swam against the tide of increasing body size through time.
"They may have derived from much older small-bodied ancestors, or adapted to evolutionary pressures occurring in small and isolated populations," says Will. Floresiensis was discovered on an Indonesian island.
"Our study shows that, other than these two species, hominins that appear after 1.4m years ago are all larger than 140cm and 40kg. This doesn't change until human bodies diversify again in just the last few thousand years."
"These findings suggest extremely strong selective pressures against small body sizes which shifted the evolutionary spectrum towards the larger bodies we have today."
Will and colleagues say evolutionary pressures that may have contributed include 'cladogenesis': the splitting of a lineage, with one line -- the smaller-bodied one, in this case -- becoming extinct, perhaps as a result of inter-species competition.
They also suggest that sexual dimorphism -- the physical distinction between genders, with females typically smaller in mammals -- was more prevalent in early hominin species but then steadily ironed out by evolution.
Study co-author Dr Jay Stock, also from Cambridge's Department of Archaeology, suggests this growth trajectory may continue.
"Many human groups have continued to get taller over just the past century. With improved nutrition and healthcare, average statures will likely continue to rise in the near future. However, there is certainly a ceiling set by our genes, which define our maximum potential for growth," Stock says.
A composite reconstruction of the earliest
known Homo sapiens fossils from Jebel Irhoud, Morocco based on micro
computed tomographic scans of multiple original fossils. Dated to 300
thousand years ago, these early Homo sapiens already have a
modern-looking face that falls within the variation of humans living
today. However, the archaic-looking braincase indicates that brain
shape, and possibly brain function, evolved within the Homo sapiens
lineage.
In 1971, anthropologist Chris Stringer traveled to museums across Europe to study and measure as many Neanderthal skulls as possible for his Ph.D. One enigmatic fossil, described as an “African Neanderthal” and dated to 40,000 years ago, particularly intrigued him. Thanks to a tip shared over coffee in Paris, he found the skull stored in another anthropologist’s cupboard.
Stringer was very puzzled by what he saw.
“I knew it was no Neanderthal,” recalled Stringer, who is now a Merit Researcher at the Natural History Museum in London. “It completely lacked their puffed-out cheek bones, mid-facial prominence, and enormous nose.”
Over the years, the fossil puzzled other scientists as well. A new excavation project began in 2004 at the site where the “African Neanderthal” was found in the 1960s — Jebel Irhoud, located west of Marrakesh in Morocco. Two new papers published in Nature report the astonishing results of this lengthy project: The so-called Neanderthal and related fossils turn out to be 300,000–350,000-year-old Homo sapiens, making them the oldest known remains for our species.
The twenty-two Homo sapiens fossils discovered so far at Jebel Irhoud push back the origins of our species by over one hundred thousand years. To put this into perspective, the prior oldest securely dated Homo sapiens fossils were known from the site of Omo Kibish in Ethiopia, and were dated to 195,000 years ago.
“Even though the Jebel Irhoud fossils currently represent the oldest Homo sapiens fossil remains, we do not believe that North Africa is the ‘cradle of humankind,’” Philipp Gunz, senior author of the first of the two papers, said.
“Instead, we argue that the first Homo sapiens dispersed all over the African continent around 300,000 years ago,” added Gunz, who is a paleoanthropologist in the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology (MPI-EVA). “These people were skilled hunters, so it is likely that they moved with their prey in the changing environments of Africa.”
View looking south of the Jebel Irhoud,
Morocco site. The remaining deposits and several people excavating them
are visible in the center. At the time the site was occupied by early
hominins, it would have been a cave, but the covering rock and much
sediment were removed by work at the site in the 1960s.
The evidence for such hunting consists of stone tools and animal remains that were found at the site with the human fossils — skulls, teeth, and long bones — that belonged to at least five individuals.
Shannon McPherron, senior author of the second paper, explained that the stone tools belong to what is known as the Middle Stone Age. Prior to this time, the predecessors of modern humans — who, with our species, comprise a group called hominins — largely relied upon big and heavy stone tools, such as hand-axes and cleavers. In the Middle Stone Age, they developed lighter and smaller tools, such as sharp pointed objects.
McPherron, an archaeologist at MPI-EVA, said many experts “think that some of the points would have served as spear points, and this would have made these Middle Stone Age peoples more effective hunters.”
Two of the new Jebel Irhoud, Morocco
fossils in situ as they were discovered during excavation. In the center
of the image, in a slightly more yellow brown tone, is the crushed top
of a human skull (Irhoud 10) and visible just above this is a partial
femur (Irhoud 13) resting against the back wall. Not visible behind the
pointed rock (between the femur and the skull) is the mandible (Irhoud
11). The scale is in centimeters.
Based on the animal remains, the early humans’ prey of choice were gazelles. Fossilized zebras, wildebeest, and hartebeest were also found at the Jebel Irhoud archaeological cave site.
The ages of the finds were determined by thermoluminescence dating of the flint artifacts, which had been heated by fire. Daniel Richter of MPI-EVA, lead author of the second paper who directed the dating work, remembered how amazed he was when the results came in.
“When I first calculated the first ages, I couldn’t believe it and re-checked all parameters several times until I was sure that my thermoluminescence ages are alright,” Richter said.
Electron spin resonance dating was also employed, and was in agreement with the other results.
Middle Stone Age tool assemblages, similar to those at Jebel Irhoud, have been found throughout Africa, supporting Gunz’s statement that early Homo sapiens were nomadic hunters. Ecological barriers, such as the vast Sahara that experiences a “greening” wet period associated with plant growth every 15,000 or so years, likely played an important role in the evolution of our species. (The Sahara is currently in a dry period.)
Some of the Middle Stone Age stone tools from Jebel Irhoud, Morocco. Pointed forms such as a–i are common in the assemblage.
“This ancient population structure might explain why Homo sapiens are so diverse, despite being so closely related genetically,” Gunz said.
Jean-Jacques Hublin, who is lead author of the first paper, Gunz, and their colleagues used state-of-the-art micro computed tomographic scans and statistical shape analysis based on hundreds of 3D measurements to show that the facial shape of the Jebel Irhoud fossils is almost indistinguishable from that of modern humans living today. The methods further indicate that a partial cranium from Florisbad, South Africa, and now dated to 260,000 years ago also belonged to a Homo sapiens.
It is little wonder then that Stringer was so puzzled by the Jebel Irhoud skull that was once incorrectly labeled as being an “African Neanderthal.”
Stringer notes that the human skulls from the Moroccan site show that these early Homo sapiens had delicate cheekbones versus those of other primates and hominins. They also possessed retracted faces and jawbones like those of people today.
The excavation area is visible as a dark notch a little more than half way down the ridge line sloping to the left.
The Moroccan human fossils, however, also reveal more primitive features, such as a longer, lower braincase, strong brow-ridges, and a larger face and teeth than what individuals have now. The braincase evidence is particularly important, as many anthropologists suspect that a series of genetic changes affecting brain connectivity, organization, and development occurred in Homo sapiens, distinguishing our species from our extinct ancestors and relatives.
Intriguingly, Stringer indicated that the fossils share some features with the remains of a hominin known as “Galilee Man” from a site called “Cave of the Robbers” of about the same age in Israel. They also share features with other hominin remains unearthed at yet another Israeli site, Tabun Cave, a rock shelter located on the edge of the coastal Mount Carmel mountain range.
While the preponderance of genetic and fossil record evidence support that the evolution of Homo sapiens took place in Africa, fossils also show that the earliest known primates originated in Asia more than 40 million years ago.
Fossils for a human-ish species called “El Graeco” from the Eastern Mediterranean were recently determined to represent the oldest known hominin. The point at which humanity diverged from other primates could have then happened in this region.
An illustration of El Graeco, foreground, living in a savannah environment in the Eastern Mediterranean 7.2 million years ago.
If such an event occurred outside of Africa, then the common ancestor of Homo sapiens, Neanderthals and Denisovans might have lived outside of Africa too, but that mystery remains unsolved.
A clearer picture is emerging concerning what happened in Africa, however.
“Twenty years ago, I thought that Homo sapiens had a rapid and punctuational origin in a single location in Africa, perhaps East Africa,” Stringer said. “Now, I think it’s more like a multiregional evolution of sapiens within Africa, with different populations separated in different regions in the bad times — with some going extinct — and connecting up and exchanging genes and behaviors in the good times, climatically speaking.”
When the discovery of Homo naledi was announced two years ago, the news prompted both amazement and incredulity. H. naledi was described as a small-bodied hominid with a brain one third the size of that of Homo sapiens. Its remains were found within the Dinaledi Chamber of the Rising Star Cave system, which is part of the Cradle of Humankind World Heritage Site northwest of Johannesburg. Some scientists believed the researchers — who published their finds in the nascent journal eLife and worked under the glare of television cameras — played fast and loose with the truth.
Now the leader of that earlier research, paleontologist Lee Berger of the University of Witwatersrand (Wits University), and his colleagues have announced via three papers in the same journal more startling finds concerning H. naledi.
They report the discovery of a second chamber within Rising Star with abundant H. naledi fossils, including one of the most complete skeletons of an early human ever found, as well as the remains of at least one child and another adult. They further mention that dating of the site and original H. naledi remains shows these individuals were alive sometime between 236,000–335,000 years ago.
Map of the Rising Star Cave System.
Berger said the earliest fossil remains of modern humans are those from the Omo Kibish region of Ethiopia and are nearly 200,000 years old. While no Homo sapiens fossils are known from subequatorial Africa as early as this, Berger and his team now believe it is possible that some populations of H. naledi came into direct contact with modern humans or their ancestors.
“We can no longer assume that we know which species made which tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioral breakthroughs in the archaeological record of Africa,” Berger said in a statement. “If there is one other species out there that shared the world with ‘modern humans’ in Africa, it is very likely there are others. We just need to find them.”
The researchers say Rising Star Cave was dated using a combination of optically stimulated luminescence of sediments with uranium-thorium dating and paleomagnetic analyses of flowstones to establish how the cave sediments relate to the geological timescale in the Dinaledi Chamber. Uranium series and electron spin resonance dating were used to determine the estimated age of H. naledi teeth.
Geologist Hannah Hilbert-Wolf studying difficult-to-reach flowstones in a small side passage in the Dinaledi Chamber.
The second and more recently discovered room in the cave was named the Lesedi Chamber. Lesedi means “light” in the Setswana language. The researchers additionally named the near-complete H. naledi skeleton found in the Lesedi Chamber: Neo. Analysis of Neo and the other remains reveals that H. naledi had features that are shared with some of the earliest known fossil members of our genus, such as Homo rudolfensis and Homo habilis, species that lived two million years ago.
The scientists believe the approximately 5-feet-tall hominid also shared features with modern humans, such as its humanlike hands, wrists, feet, and lower limbs. H. naledi’s anatomy suggests to the researchers that it was both an effective walker and climber.
“Neo” skull of Homo naledi, frontal view.
“Lucy,” the 3.2-million-year-old skeleton
of the hominid Australopithecus afarensis (left) and “Neo,” a skeleton
of Homo naledi (right) that was dated as being roughly 250,000 years
old.
The Lesedi Chamber is about 109 yards from the Dinaledi Chamber, where at least 15 individuals of various ages were found. Both chambers are difficult to access.
“I have never been inside either of the chambers, and never will be,” co-author John Hawks of the University of Wisconsin-Madison and Wits University said in a statement. “In fact, I watched Lee Berger being stuck for almost an hour, trying to get out of the narrow underground squeeze of the Lesedi Chamber.”
Berger eventually had to be extricated using ropes tied to his wrists.
The remoteness and distance between the cave chambers suggests to the researchers that H. naledi was caching its dead, and likely was controlling fire to see within the deep, dark cave. No tools directly associated with this species of human have been found yet, though.
Chris Stringer, a merit researcher at the Natural History Museum in London, is a leading expert on early human origins. He expressed amazement over the conclusion that H. naledi lived around 300,000 years ago.
“This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk, and hip joint,” Stringer said. “Yet the wrist, hands, legs and feet look more like those of Neanderthals and modern humans, and the teeth are relatively small and simple, and set in lightly built jawbones.”
He believes that H. naledi could be a “relic species, retaining many primitive traits from a much earlier time.” Homo floresiensis, aka the Hobbit Human that lived until relatively recently, came to his mind. The diminutive Hobbits are thought to have lived when several other species of humans were in Europe and Asia. H. floresiensis lived on the island of Flores, however, so isolation at that location could help to explain how it remained a distinct species of human.
H. naledi does not appear to have been isolated, so Stringer posed the compelling question: “How did a comparably strange and small-brained species linger on in southern Africa, seemingly alongside more ‘advanced’ humans?”
Homo naledi was very different from
archaic humans that lived around the same time. Kabwe skull from Zambia,
an archaic human (left) and ''Neo'' skull of Homo naledi (right).
He also questioned the theory that H. naledi cached its dead, and has not ruled out that accidental or natural processes resulted in the placement of the remains in the two remote cave chambers.
Nevertheless, Stringer said that the discovery and dating of H. naledi “remind us that about 95 percent of the area of Africa is still essentially unexplored for its fossil human record, and its history even within the last 500,000 years may well be as complex as that of Eurasia with its 5 known kinds of humans — Homo erectus, heidelbergensis, neanderthalensis, Denisovans, and floresiensis.”
This is the sagittal crest of a male gorilla skull.
A new study from The Australian National University (ANU) of the bony head-crests of male gorillas could provide some of the first clues about the social structures of our extinct human relatives, including how they chose their sexual partners.
The study looks at the sagittal crest, a bone ridge on the top of the skull, in four species of apes.
Lead researcher of the study Dr Katharine Balolia of the ANU School of Archaeology and Anthropology said that while the crests were long thought to develop in apes to provide extra space for the muscles used for chewing, this study indicates they could also be a form of social signalling that results from sexual selection.
"We found that for male gorillas and orangutans, it is not just chewing that drives crest formation. There is also a social element to it. For example, females prefer male gorillas with larger sagittal crests," Dr Balolia said.
Dr Balolia said the findings may provide clues to the social structures of some extinct human relatives.
"Some species of extinct human relatives have a sagittal crest," she said.
"And if sagittal crest size and social behaviour are linked in this way, then we could potentially establish that some of our extinct human relatives had a gorilla-like social system.
"This would be a first, because otherwise the human fossil record provides precious little about how our extinct relatives chose their mates."
The study used 3D scans of skull specimens and found two lines of evidence to support the finding.
"In terms of gorilla social structures, the males establish dominance shortly after their wisdom teeth emerge. We found the sagittal crest appears right after their wisdom teeth emerge, so that fits in with the timing of social dominance," she said.
"In contrast, in orangutans some males only become dominant quite late in their adult life, and the sagittal crest appears later," she said.
In addition, statistical modelling suggests that, when present, crests in gorillas and orangutans are larger than what would be expected if they were simply there to provide more space for the larger chewing muscles needed by the big males.
