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Archive for the ‘EVOLUTION’ Category

Creatures Lived On Land 2.2 Billion Years Ago

“Researchers at the University of Oregon have recently unearthed fossils in South Africa that present evidence of life on land 2.2 billion years ago—four times older than traditionally thought.

The fossilized organisms, dubbed Diskagma buttonii, are no bigger than the size of a standard match head and were found threaded together in bunches. Though researchers are still unsure as to their biological function, the organisms most closely resemble a modern fungus calledGeosiphon. The team believes Diskagma could be the oldest known eukaryote, a cellular organism containing a nucleus.

The results of the study, led by geologist Gregory J. Retallack, provide new insight into the development of Earth’s atmosphere. Examining the fossils suggests that the greening of Earth, involving the rise of oxygen and emergence of new plant and animal forms, occurred much earlier than 500 million years ago, the previous estimate.”


Scientists find oldest dinosaur

“Researchers have discovered what may be the earliest dinosaur, a creature the size of a Labrador retriever, but with a five foot-long tail, that walked the Earth about 10 million years before more familiar dinosaurs… The findings mean that the dinosaur lineage appeared 10 million to 15 million years earlier than fossils previously showed, originating in the Middle Triassic rather than in the Late Triassic period.”

New Statistical Model Moves Human Evolution Back Three Million Years

November 5, 2010 – Original Source: ScienceDaily

Evolutionary divergence of humans and chimpanzees likely occurred some 8 million years ago rather than the 5 million year estimate widely accepted by scientists, a new statistical model suggests.

The revised estimate of when the human species parted ways from its closest primate relatives should enable scientists to better interpret the history of human evolution, said Robert D. Martin, curator of biological anthropology at the Field Museum, and a co-author of the new study appearing in the journal Systematic Biology.

Working with mathematicians, anthropologists and molecular biologists, Martin has long sought to integrate evolutionary information derived from genetic material in various species with the fossil record to get a more complete picture.

Comparing DNA among related animals can provide a clear picture of how their shared genes evolved over time, giving rise to new and separate species, Martin said. But such molecular information doesn’t yield a timetable showing when the genetic divergence occurred.

Fossil evidence is the only direct source of information about long-extinct species and their evolution, Martin and his colleagues said, but large gaps in the fossil record can make such information difficult to interpret. For a generation, paleontologists have estimated human origins at 5 million to 6 million years ago.

But that estimate rests on a thin fossil record. By looking at all of today’s primate species, all of the known fossil primates and using DNA evidence, computer models suggest a longer evolutionary timetable. The new analysis described in the Systematic Biology paper takes into account gaps in the fossil record and fills in those gaps statistically.

Such modeling techniques, which are widely used in science and commerce, take into account more overall information than earlier processes used to estimate evolutionary history using just a few individual fossil dates, Martin said. It can give scientists a broader perspective for interpreting data.

One example is a skull fossil discovered in Chad (central Africa) earlier in this decade. The fossil, named Sahelanthropus tchadensis and nicknamed Toumaï (which means “hope of life” in the local Goran language), raised great interest because it has many human characteristics. But consensus on how to classify the discovery has been elusive particularly because the fossil is about 7 million years old, well beyond the accepted time frame for human evolution.

Under the new estimate, Toumaï would fall within the period after the human lineage split from chimpanzees, Martin said.

The new approach to dating evolutionary history builds on earlier work by Martin and colleagues. In 2002, they published a paper in Nature that argues the last common ancestor of today’s primates lived some 85 million years ago.

This implies that for 20 million years before dinosaurs became extinct, early versions of primates also lived and evolved. It challenged the accepted theory that primates and other mammals didn’t really thrive on the planet until dinosaurs were gone.

After that paper was published, Martin said he expected someone would apply the new statistical techniques to the question of human evolution, but when no one did, “We decided to do it ourselves.”

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Field Museum, via EurekAlert!, a service of AAAS.

Journal Reference:

  1. R. D. Wilkinson, M. E. Steiper, C. Soligo, R. D. Martin, Z. Yang, S. Tavare. Dating Primate Divergences through an Integrated Analysis of Palaeontological and Molecular Data. Systematic Biology, 2010; DOI: 10.1093/sysbio/syq054

Neanderthals More Advanced Than Previously Thought: They Innovated, Adapted Like Modern Humans, Research Shows

September 22, 2010 – Original Source: ScienceDaily

For decades scientists believed Neanderthals developed `modern’ tools and ornaments solely through contact with Homo sapiens, but new research from the University of Colorado Denver now shows these sturdy ancients could adapt, innovate and evolve technology on their own.

The findings by anthropologist Julien Riel-Salvatore challenge a half-century of conventional wisdom maintaining that Neanderthals were thick-skulled, primitive `cavemen’ overrun and outcompeted by more advanced modern humans arriving in Europe from Africa.

“Basically, I am rehabilitating Neanderthals,” said Riel-Salvatore, assistant professor of anthropology at UC Denver. “They were far more resourceful than we have given them credit for.”

His research, to be published in December’s Journal of Archaeological Method and Theory, was based on seven years of studying Neanderthal sites throughout Italy, with special focus on the vanished Uluzzian culture.

About 42,000 years ago, the Aurignacian culture, attributed to modern Homo sapiens, appeared in northern Italy while central Italy continued to be occupied by Neanderthals of the Mousterian culture which had been around for at least 100,000 years. At this time a new culture arose in the south, one also thought to be created by Neanderthals. They were the Uluzzian and they were very different.

Riel-Salvatore identified projectile points, ochre, bone tools, ornaments and possible evidence of fishing and small game hunting at Uluzzian archeological sites throughout southern Italy. Such innovations are not traditionally associated with Neanderthals, strongly suggesting that they evolved independently, possibly due to dramatic changes in climate. More importantly, they emerged in an area geographically separated from modern humans.

“My conclusion is that if the Uluzzian is a Neanderthal culture it suggests that contacts with modern humans are not necessary to explain the origin of this new behavior. This stands in contrast to the ideas of the past 50 years that Neanderthals had to be acculturated to humans to come up with this technology,” he said. “When we show Neanderthals could innovate on their own it casts them in a new light. It `humanizes’ them if you will.”

Thousands of years ago, southern Italy experienced a shift in climate, becoming increasingly open and arid, said Riel-Salvatore. Neanderthals living there faced a stark choice of adapting or dying out. The evidence suggests they began using darts or arrows to hunt smaller game to supplement the increasingly scarce larger mammals they traditionally hunted.

“The fact that Neanderthals could adapt to new conditions and innovate shows they are culturally similar to us,” he said. “Biologically they are also similar. I believe they were a subspecies of human but not a different species.”

The powerfully built Neanderthals were first discovered in Germany’s Neander Valley in 1856. Exactly who they were, how they lived and why they vanished remains unclear.

Research shows they contributed between 1 and 4 percent of their genetic material to the people of Asia and Europe. Riel-Salvatore rejects the theory that they were exterminated by modern humans. Homo sapiens might simply have existed in larger groups and had slightly higher birthrates, he said.

“It is likely that Neanderthals were absorbed by modern humans,” he said. “My research suggests that they were a different kind of human, but humans nonetheless. We are more brothers than distant cousins.”

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Colorado Denver.

Journal Reference:


  1. Julien Riel-Salvatore. A Niche Construction Perspective on the Middle–Upper Paleolithic Transition in Italy. Journal of Archaeological Method and Theory, 2010; DOI: 10.1007/s10816-010-9093-9

‘Mitochondrial Eve’: Mother of All Humans Lived 200,000 Years Ago

August 17, 2010 – Original Source: ScienceDaily

The most robust statistical examination to date of our species’ genetic links to “mitochondrial Eve” — the maternal ancestor of all living humans — confirms that she lived about 200,000 years ago. The Rice University study was based on a side-by-side comparison of 10 human genetic models that each aim to determine when Eve lived using a very different set of assumptions about the way humans migrated, expanded and spread across Earth.

The research is available online in the journal Theoretical Population Biology.

“Our findings underscore the importance of taking into account the random nature of population processes like growth and extinction,” said study co-author Marek Kimmel, professor of statistics at Rice. “Classical, deterministic models, including several that have previously been applied to the dating of mitochondrial Eve, do not fully account for these random processes.”

The quest to date mitochondrial Eve (mtEve) is an example of the way scientists probe the genetic past to learn more about mutation, selection and other genetic processes that play key roles in disease.

“This is why we are interested in patterns of genetic variability in general,” Kimmel said. “They are very important for medicine.”

For example, the way scientists attempt to date mtEve relies on modern genetic techniques. Genetic profiles of random blood donors are compared, and based upon the likenesses and differences between particular genes, scientists can assign a number that describes the degree to which any two donors are related to one another.

Using mitochondrial genomes to gauge relatedness is a way for geneticists to simplify the task of finding common ancestors that lived long ago. That is because the entire human genome contains more than 20,000 genes, and comparing the differences among so many genes for distant relatives is problematic, even with today’s largest and fastest supercomputers.

But mitochondria — the tiny organelles that serve as energy factories inside all human cells — have their own genome. Besides containing 37 genes that rarely change, they contain a “hypervariable” region, which changes fast enough to provide a molecular clock calibrated to times comparable to the age of modern humanity. Because each person’s mitochondrial genome is inherited from his or her mother, all mitochondrial lineages are maternal.

To infer mtEve’s age, scientists must convert the measures of relatedness between random blood donors into a measure of time.

“You have to translate the differences between gene sequences into how they evolved in time,” said co-author Krzysztof Cyran, vice head of the Institute of Informatics at Silesian University of Technology in Gliwice, Poland. “And how they evolved in time depends upon the model of evolution that you use. So, for instance, what is the rate of genetic mutation, and is that rate of change uniform in time? And what about the process of random loss of genetic variants, which we call genetic drift?”

Within each model, the answers to these questions take the form of coefficients — numeric constants that are plugged into the equation that returns the answer for when mtEve lived.

Each model has its own assumptions, and each assumption has mathematical implications. To further complicate matters, some of the assumptions are not valid for human populations. For example, some models assume that population size never changes. That is not true for humans, whose population has grown exponentially for at least several thousand generations. Other models assume perfect mixing of genes, meaning that any two humans anywhere in the world have an equal chance of producing offspring.

Cyran said human genetic models have become more complex over the past couple of decades as theorists have tried to correct for invalid assumptions. But some of the corrections — like adding branching processes that attempt to capture the dynamics of population growth in early human migrations — are extremely complex. Which raises the question of whether less complex models might do equally well in capturing what’s occurring.

“We wanted to see how sensitive the estimates were to the assumptions of the models,” Kimmel said. “We found that all of the models that accounted for random population size — such as different branching processes — gave similar estimates. This is reassuring, because it shows that refining the assumptions of the model, beyond a certain point, may not be that important in the big picture.”

The research was supported by grants from the Polish Ministry of Science and Higher Education and the Cancer Prevention and Research Institute of Texas. It has resulted from a standing collaboration between Rice University and Silesian University of Technology.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University.

Journal Reference:


  1. Cyran et al. Alternatives to the Wright-Fisher model: The robustness of mitochondrial Eve dating. Theoretical Population Biology, 2010; DOI: 10.1016/j.tpb.2010.06.001

Meet X-woman: a possible new species of human

March 24, 2010 – Original Source: New Scientist

The human family tree may be in for a dramatic rewrite. DNA collected from a fossilised finger bone from Siberia shows it belonged to a mysterious ancient hominid – perhaps a new species.

“X-woman”, as the creature has been named, last shared an ancestor with humans and Neanderthals about 1 million years ago but is probably different from both species. She lived 30,000 to 50,000 years ago.

“This is the tip of the iceberg,” says Chris Stringer, a palaeoanthropologist at the Natural History Museum in London who was not involved in the find. More hominids that are neither Neanderthal nor human are likely to be discovered in coming years, particularly in central and eastern Asia, he says.

Roaming Asia

Previously, anthropologists thought that Neanderthals and humans were the only hominids roaming Europe and Asia during the late Pleistocene. The discovery of 17,000-year-old Homo floresiensis – the “hobbit” – dispelled that notion, but many anthropologists look on H. floresiensis as an anomaly, isolated from the human–Neanderthal hegemony on the mainland.

The newly discovered creature, which probably lived in close proximity to humans and Neanderthals, suggests that things were not that simple. “The picture that’s going to emerge in the next years is a much more complex one,” says Svante Pääbo, a palaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Pääbo and colleague Johannes Krause discovered the specimen in the Denisova cave in southern Siberia, and sequenced DNA from its mitochondria. It is impossible to say what the creature would have looked like based on a single pinkie bone, so Pääbo and Krause are hesitant to call it a new species.

Though the creature’s sex is not known, they are for now referring to her as X-woman because mitochondria are inherited maternally. “No one really knows what she would look like,” Pääbo says.

X-woman’s mitochondria differ from a human’s at nearly 400 DNA letters; Neanderthals show only half as many differences.

African ancestry

This suggests that X-woman shared an African ancestor with the two other species somewhere between 780,000 and 1.3 million years ago, before striking north and east. This expansion is distinct from the one that occurred around 500,000 years ago that gave rise to Neanderthals, and from our own species’ peregrinations from about 50,000 years ago.

The split seems too recent for X-woman to be related to Homo erectus, which began moving out of Africa around 2 million years ago.

However, Clive Finlayson, a palaeoanthropologist at the Gibraltar Museum, says the idea that there were just a handful of hominid migrations out of Africa is a vast oversimplification that ignores how other species expand their range over time. “To talk about one or two expansions from a particular region doesn’t make any biological sense,” he says. “There were probably hundreds, thousands of migrations out of Africa.”

Though there is no complete skeleton for X-woman, her lineage could mean she is related to any number of more complete specimens recovered in Asia that don’t neatly fit human or Neanderthal body patterns, says Stringer. “This new DNA work provides an entirely new way of looking at the still poorly understood evolution of humans in central and eastern Asia.”

Nuclear DNA

Pääbo and his team are hesitant to speculate too much about X-woman’s nature until they obtain DNA sequences from the nuclear genome’s 3.1 billion letters. That project is already under way, and the first results should come within months. Pääbo’s team will likely want X-woman’s genome to answer the same questions they are asking of the Neanderthal genome, which is due for publication soon.

For instance, humans and Neanderthals share unique mutations in a gene linked to speech and language called FOXP2. If X-woman’s sequence is complete enough, they will be able to determine if it possesses the same change – and potentially the capability for language.

There is no sign in X-woman’s mitochondrial genome that her kind interbred with humans or Neanderthals, but the nuclear genome will offer a far better chance of finding out.

Neanderthal neighbours

Given the close proximity of Neanderthal remains dated to the same time and artefacts that appear to be human, interbreeding is not unlikely, Pääbo says. “Having in about the same time window three different forms [of hominids], increases the potential of all types of interactions, including genetic.”

X-woman’s mitochondrial DNA begins to paint a picture of what she was like, if only a blurry one. The protein-coding genes do not contain any surprising mutations that would cause disease.

Finlayson would love to link X-woman to other bones, and even stone technologies, though the chances of doing this may be slim. “Ideally we would like to have all that information, but we don’t. The fact that we’ve got this genetic result is important, it’s very important.”

Pääbo hopes that such a connection will come through sequencing DNA from other Asian hominid fossils. But he, too, is prepared for the possibility that such bones may never turn up.

He sees in X-woman the beginning of a new way of understanding human history. “It gives another picture of our past, a molecular picture of the evolution of our genome” which he says is in some aspects even more conclusive than fossils.

Journal reference: Nature, DOI: 10.1038/nature08976

Fossils shake up our family tree

April 8, 2010 – Original Source: Cosmic Log, MSNBC

Rock partially encases the cranium of a juvenile male representing the species designated Australopithecus sediba. The skull was found in a South African cave. Brett Eloff / Courtesy of Lee Berger, Univ. of the Witwatersrand

Well-preserved fossils found in a South African cave pit mark an important transition between the 3.2 million-year-old pre-human known as Lucy and our own branch of the evolutionary family tree. That much, anthropologists can agree on. But exactly where do they fit in that transition? That’s the subject of a high-profile debate.

It may be tempting to call these fossils a “missing link,” as some of the leaked news reports did earlier this week. But scientists say that’s too simplistic a term for what the bones signify.

There are so many elements to the tale that it’s hard to know where to start. Here are the main points relating to the find, announced today by the journal Science:

  • Scientists say the two partial hominid skeletons are between 1.78 million and 1.95 million years old, going back to a time that has been little-documented in our ancestry.
  • The place where the bones were found, known as the Malapa cave, was identified using a Google Earth survey. The first bone was spotted not by a professional scientist, but by the 9-year-old son of one of the researchers.
  • The research team determined that the fossils came from an adult woman and a boy who might have been a relative, or even her son. Geologists surmise that they fell down the cave opening and were swept into a “death trap” that played a big role in preserving the remains.
  • The skeletons appear to represent a transitional species in the human family tree, with some characteristics in common with Lucy, and others in common with extinct members of our own Homo genus.
  • The discoverers decided to put these fossils in the same genus as Lucy, giving them the scientific name Australopithecus sediba.

“Sediba” means “wellspring” in southern Africa’s Sesotho language, and the discoverers believe the species may have been the wellspring for the origins of the genus Homo. But the anthropologist who found Lucy thinks that the discoverers are wrong, and that the fossils actually represent a species within Homo – and not even the oldest example of a Homo ancestor.

The sharp differences of opinion demonstrate that tracing human origins is not a simple exercise. The full picture is likely to be more nuanced and less sharply delineated than the neat diagrams you may have studied in biology class.

Debate over the family tree

The lead author of one of the studies in Science, Lee Berger of South Africa’s University of Witwatersrand, said the fossils “fill a critical gap … lying between the australopithecines and most probably early members of the genus Homo.” He also said the fossils “might be a Rosetta Stone, effectively, to defining for the first time just what the genus Homo is.”

But he shied away from using the “missing link” label.

” I don’t like the use of that term, because I think it’s a Victorian term,” he said during a teleconference in advance of today’s publication. “It implies some ‘chain’ of evolution.” Rather, he preferred to characterize the newfound species as “highly transitional,” blending characteristics from earlier australopiths and later humans.

Scientists say that australopiths like Lucy (known as Australopithecus afarensis) were capable of walking upright, but were adapted for climbing in trees as well. They had powerful upper bodies and long, strong arms suited for that purpose. They also had relatively small brains and small stature. Lucy, for example, had a brain one-third the size of ours and stood about 42 inches (1.07 meters) tall.

The South African creatures were about 25 percent taller than Lucy, but had similar-sized skulls that Berger said might have given them a “pinhead” appearance in life. The teeth were smaller than Lucy’s, like those of an early Homo species. Their legs were longer, and the pelvis was built better for striding or running on the African savanna. Those adaptations would tend to put them on the Homo side of the line.

The bones of a juvenile male (left) and an adult female (right), recovered from the Malapa cave pit in South Africa, are arranged on an idealized outline of an Australopithecus africanus skeleton.

But Berger said he and his colleagues decided to put the fossils in the Australopithecus category instead, because of the creatures’ arms as well as their brain size. The arms were long, like Lucy’s, and that suggested that the newfound hominids were still “dependent on the trees for some of its survival – it’s clearly climbing.”

Not everyone agrees with that decision. The anthropologist who discovered Lucy 35 years ago, Donald Johanson of Arizona State University, told me in an e-mail that Berger’s team “missed the boat” by classifying the fossils as australopiths rather than a Homo species. In effect, Johanson was saying that Berger was putting his find on the wrong branch of humanity’s family tree. (Read the full e-mail from Johanson below.)

Berger, meanwhile, said that Johanson and his colleagues might have misclassified some of the hominid fossils they found in Ethiopia. Those fossils, which date back 2.33 million years, were put in the Homo category on the basis of an upper jaw. Berger said the latest discovery suggested that a more complete set of bones was required to determine where fossils fit in the family tree.

“This may be a particularly mosaic species, you must always consider that,” Berger said of his find. “You may also have to consider that we may need more, stronger criteria to include things in either genera or even possibly species.” (Read Berger’s FAQ about the find below.)

If the past is any guide, the debate over where these newfound fossils fit into the evolutionary family tree could go on for years. With each significant discovery, anthropologists generally find that the tree is more tangled than they previously thought. Last month’s revelation about a 40,000-year-old hominid bone that didn’t match up genetically with either modern Homo sapiens or extinct Homo neanderthalensis is another example of that phenomenon at work.

The debate isn’t trivial: It has to do with when and where our own branch of the hominid family tree from the line of now-extinct creatures like Lucy.

How the fossils were found

The saga of how the South African fossils were found adds to the intrigue. “Google Earth is really the reason I found the site,” Berger said.

The anthropologist started using the 3-D mapping program in 2008 to look for caves in a fossil-rich region outside Johannesburg known as the Cradle of Humankind World Heritage Site. He and a colleague from Australia’s James Cook University, Paul Dirks, found hundreds of previously unknown caves – and that summer they went on an expedition to explore a particularly promising area.

Berger found a rich fossil site in the Malapa cave almost immediately. Two weeks later, he returned to the cave with his 9-year-old son, Matthew, and his post-doctoral student, Job Kibii. It took Matthew only a couple of minutes to find the collarbone of a hominid. When the elder Berger looked around the block of stone where the bone was found, he discovered other bones as well.

Eventually, Berger and his team uncovered the partial skeletons of two individuals that were encased in a cement-like sediment.

The bone that Matthew found apparently belonged to a juvenile male. Based on an analysis of the teeth and other bones, the team believes the child was the equivalent of 10 to 13 years old in human developmental terms – or 8 to 9 years old in actual age. The fossil will be given a nickname in a contest open to South African children, Berger said.

The researchers believe that the other skeleton is that of an adult female, perhaps in her late 20s or older. That assessment is based on the pattern of tooth wear as well as the shape of the jaw and hips. Both individuals would have been about 4-foot-2 (127 centimeters) in height. Their weights would have been around 73 pounds (33 kilograms) for the female, and 60 pounds (27 kilograms) for the male.

Several techniques, including uranium-lead dating and paleomagnetic dating, were used to determine that the bones were about 1.9 million years old. Their arrangement in the cave suggested that they died within days or hours of each other. The bones of other animals from the same epoch were found encased nearby.

Researcher Paul Dirks stands in the Malapa cave site shortly after it was first discovered and before excavations began. Courtesy of Paul Dirks

How the hominids died

A separate research paper in Science, with Dirks as the lead author, combines all these clues with the geological data to suggest how the hominids died.

The site might once have been a complex cave system with deep vertical shafts that might have served as “death traps” on the surface. “Animals might have been attracted to the smell of water coming from the shaft, and carnivores might have been attracted to the smell of decomposing bodies,” the researchers wrote.

The two hominids might have been looking for water when they ended up among the victims of a death trap. “You may think that it’s possible when you start climbing down, and then you go ‘oops,’ and then it turns out not to be possible, and there’s only one way to go, and that’s to go down,” Dirks said.

Berger said the fact that the bones of many animals were found together, with no evidence of scavenging, suggests that their end came quickly. “None of them were alive enough to feed or scavenge on anything else,” he said.

Later, flooding water might have washed the remains of the animals – including the hominids – deeper into the cave system, down into an underground holding area where sediment could encase the remains for preservation. The researchers suggest that the roof of the cave system eventually collapsed and became eroded, exposing the sediment so that 9-year-old Matthew could discover the spot.

A cartoon shows how two hominids might have become trapped and buried in sediments at the bottom of a cave system. Science / AAAS

Were the adult female and the juvenile male possibly a mother and her son? “If they behaved anything like any modern primates, including humans, they probably would have been territorial, part of the same troop,” Berger said. “They would have known each other in life, and they probably would have been part of a troop. And that gives a very high probability that they would have been related to each other.”

Berger said he and his colleagues are looking at ways to confirm whether there was a relationship – and suggested that they’re considering molecular analysis of material extracted from the bones, as has been done with tyrannosaur tissue.

“We are seeing some organics preserved in various parts of the assemblage,” Berger said. He noted that genetic analysis has never been done on hominid fossils as old as the ones found in South Africa, “but we are trying everything possible and are exploring the possibility that there could be at least proteins and possibly DNA preserved.”

He also said at least two more skeletons have been found at the site, and wouldn’t rule out the possibility that tools or other artifacts might be found as well. All of which means the story of the Malapa hominids is just beginning.

“They are going to be a remarkable window, a time machine of morphology into the evolutionary processes and evolutionary stresses going on at that period between 1.8 and 2 million years,” Berger said.

Postscript 1: Here’s a rundown of frequently asked questions (and answers) written by Berger:

What does Australopithecus sediba mean?
Australopithecus means “southern ape,” after the genus of the Taung child, named by Professor Raymond Dart, also from the University of the Witwatersrand, Johannesburg. Sediba means natural spring, fountain or wellspring in Sotho, an appropriate name for a species that might be the point from which the genus Homo arises.

What is a hominid/hominin?
A hominid is a member of the taxonomic family that includes humans, chimpanzees, gorillas and their extinct ancestors. Hominins are members of the human branch after the human lineage split from that of chimpanzees, and thus include living humans and extinct human ancestors, such as the Australopiths. Hominins are characterised by bipedal locomotion, although this may not have been the case for the very earliest members of the group, and relatively small canine teeth. Later members of this group (those in the genus Homo) are characterized by larger brains than those of living apes like chimpanzees, bonobos, gorillas, orangutans and gibbons.

How were the fossils dated?
They were dated using a variety of methods including uranium-lead, paleomagnetic and faunal dating systems. Cosmogenic dating was used to interpret the landscape formation and to determine the depth of the cave at the time.

How were the individuals preserved?
The site where the fossils were discovered is technically the infill of a de-roofed cave that was about 50 meters underground 1.9 million years ago. The individuals appear to have fallen, along with other animals, into a deep cave, landing up on the floor for a few days or weeks. The bodies were then washed into an underground lake or pool, probably pushed there by a large rainstorm. They did not travel far, maybe a few meters, where they were solidified, as if thrown into quick-setting concrete. The rock they are preserved in is called calcified clastic sediment. Over the past 1.9 million years the land has eroded to expose the fossil-bearing sediments.

Did they die at the same time, or was it a catastrophe?
The hominin skeletons were found with the bones either in partial articulation or in close anatomical association, which suggests that both bodies were only partially decomposed at the time of deposition in the lower chamber. This further suggests that they died very close in time to each other, either at the same time, or hours, days or weeks apart.

How old is the child?
The juvenile is around 10 to 13 years old in human developmental terms. He was probably a bit younger in actual age (perhaps as young as eight or nine or so) as he is likely to have matured faster than humans. The age estimate is based on modern human standards by which the eruption stages of the teeth are evaluated and the degree of development of the growth centers of the bones.

How old is the female skeleton?
Based on the extreme wear of her teeth, she is probably at least in her late 20s or early 30s.

Did she have children?
It is likely that a female Australopith of her age would have had children.

How do you know the child is a male?
There are features of the face that help us determine that the child is a male. The muscles of the child are larger than that of the other skeleton, even though it is a child. There are also features of the pelvis that we can use to determine that it is a male.

How does this find relate to Lucy?
Australopithecus sediba is approximately a million years younger than Lucy. Some scientists feel that Lucy’s species, Au. afarensis, gave rise to Au. africanus, and Lee et al. are suggesting that Au. africanus or something similar gave rise to Au. sediba.

How do you know that it is a new species?
The team compared the skeletons with all the remains of fossil hominids that have been discovered and in many ways they are absolutely unique from any fossil species found.

Why is this not the genus Homo?
The fossils have an overall body plan that is like that of other Australopiths – they have small brains, relatively small bodies and long and seemingly powerful arms. They do have some features in the skull and pelvis that are found in members of the genus Homo but not in other Australopiths. However, given the small brains and Australopith-like upper body, the team felt that keeping this species in the genus Australopithecus was the conservative thing to do.

What about Homo habilis?
Our study indicates that Australopithecus sediba may be a better ancestor of Homo erectus and it may certainly help to clear up some of this “muddle in the middle.”

Why is there still rock attached to the child’s skull?
Due to the fragility of the base of the cranium of the specimen and to preserve part of the adhering matrix for future research, the team has decided to leave the specimen partially in rock. The team has been able to visualize this hidden part using scanning technology.

Postscript 2: Here’s the e-mail response from paleoanthropologist Donald Johanson of Arizona State University, who discovered the Lucy fossil in 1974:

“The South African finds from Malapa are most interesting, but I find it curious that the authors point to so many anatomical features that indicate that the finds belong to our genus, Homo, yet they place it in Australopithecus, so I think they missed the boat here.  Finding 1.8 million-year-old Homo in southern Africa is newsworthy since previous traces have been fragmentary and controversial.

“Additionally I do not see these fossils as evolving from Australopithecus africanus, which I believe gave rise to A. robustus in south Africa.  The specimens from Malapa are not the ancestor to later all Homo as the authors believe, since we have evidence of Homo in eastern africa at 2.33 million years. My team found an upper jaw of this age in the younger sediments at Hadar where Lucy was found, and this palate represents the oldest anatomical evidence, thus far, for our genus. It is probably best attributed to Homo habilis. Let us not forget that the Turkana Boy is about 1.8 million years old and is without doubt Homo and is attributed to Homo ergaster.

“The Malapa hominids, with so many Homo features, but with relatively short limbs, resembles Olduvai Hominid 62 which we found in the mid-’80s. Although fragmentary, OH 62 does have relatively shorter legs and longer arms, like earlier Australopithecus, and the appearance in the fossil record of a more modern body build, as in the Turkana Boy, comes later.  However the Olduvai material, OH 62 and several other specimens, are attributed to Homo on the basis of diagnostic features in the teeth, jaws and cranium.  Some scholars have suggested we place H. habilis into the genus Australopithecus and until there is a modern body build Homo should not be used as the genus for these fossils.

“It is also rather possible that Homo, like Australopithecus, underwent a diversification (adaptive radiation) resulting in several different species. This would not be unusual.  However, within the greater framework of Australopithecus and Homo, I believe emphasis should be placed on the diagnostic anatomy of the teeth, jaws and cranium…. So, I would continue to use Homo for habilis, and for these new specimens from Malapa.  Until a more comprehensive comparative study is undertaken (I know other specimens have been recovered from the site), the relationship between the Malapa material and Homo in eastern Africa is not very clear.  I would not be surprised if the Malapa material represents a newly recognized species of Homo.

“The South African finds, about half a million years younger, are probably descendants of the eastern Africa Homo. 500,000 years is a long time, and Homo could easily have migrated from eastern to southern Africa in that time.

“There are two partial skeletons, one a female and the other a male.  The skull of the male is refreshingly complete and should be attributed to Homo. Just after Lee found the first hominids at Malapa he invited me to see the material at Wits. The mandible is lightly built, not very deep or thick resembling Homo. The first and second permanent molars are erupted and there is little occlusal wear, suggesting a diet quite different from Australopithecus. In Australopithecus by the time the second molar erupts the first shows rather heavy wear.  Also, the teeth are small in size, like in Homo, and unlike Australopithecus.

“We have a very comprehensive understanding of the dating, diversity and relationships between the species of Australopithecus, but we know relatively little about the origins of our own genus. Thus, anything found that represents early Homo is potentially of some importance.  I think these finds will refocus attention on the South African fossil sites and strengthen the importance of these sites for a more complete understanding of the human family tree.”

Authors of the paper about the hominid fossils include Berger, Dirks and Kibii as well as Darryl J. de Ruiter, Steven E. Churchill, Peter Schmid and Kristian J. Carlson. Authors of the paper about the geological setting include Dirks, Kibii, Churchill and Berger as well as Brian F. Kuhn, Christine Steininger, Jan D. Kramers, Robyn Pickering, Daniel L. Farber, Anne-Sophie Meriaux, Andy I.R. Herries and Geoffrey C.P. King.

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