High population density triggers cultural explosions

Increasing population density, rather than boosts in human brain power, appears to have catalysed the emergence of modern human behaviour, according to a new study by UCL (University College London) scientists published in the journal Science. High population density leads to greater exchange of ideas and skills and prevents the loss of new innovations. It is this skill maintenance, combined with a greater probability of useful innovations, that led to modern human behaviour appearing at different times in different parts of the world.

In the study, the UCL team found that complex skills learnt across generations can only be maintained when there is a critical level of interaction between people. Using computer simulations of social learning, they showed that high and low-skilled groups could coexist over long periods of time and that the degree of skill they maintained depended on local population density or the degree of migration between them. Using genetic estimates of population size in the past, the team went on to show that density was similar in sub-Saharan Africa, Europe and the Middle-East when modern behaviour first appeared in each of these regions. The paper also points to evidence that population density would have dropped for climatic reasons at the time when modern human behaviour temporarily disappeared in sub-Saharan Africa.

Adam Powell, AHRC Centre for the Evolution of Cultural Diversity, says: "Our paper proposes a new model for why modern human behaviour started at different times in different regions of the world, why it disappeared in some places before coming back, and why in all cases it occurred more than 100,000 years after modern humans first appeared.

"By modern human behaviour, we mean a radical jump in technological and cultural complexity, which makes our species unique. This includes symbolic behavior, such as abstract and realistic art, and body decoration using threaded shell beads, ochre or tattoo kits; musical instruments; bone, antler and ivory artefacts; stone blades; and more sophisticated hunting and trapping technology, like bows, boomerangs and nets.

Professor Stephen Shennan, UCL Institute of Archaeology, says: "Modern humans have been around for at least 160,000 to 200,000 years but there is no archaeological evidence of any technology beyond basic stone tools until around 90,000 years ago. In Europe and western Asia this advanced technology and behaviour explodes around 45,000 years ago when humans arrive there, but doesn't appear in eastern and southern Asia and Australia until much later, despite a human presence. In sub-Saharan Africa the situation is more complex. Many of the features of modern human behaviour – including the first abstract art – are found some 90,000 years ago but then seem to disappear around 65,000 years ago, before re-emerging some 40,000 years ago.

"Scientists have offered many suggestions as to why these cultural explosions occurred where and when they did, including new mutations leading to better brains, advances in language, and expansions into new environments that required new technologies to survive. The problem is that none of these explanations can fully account for the appearance of modern human behaviour at different times in different places, or its temporary disappearance in sub-Saharan Africa."

Dr Mark Thomas, UCL Genetics, Evolution and Environment, says: "When we think of how we came to be the sophisticated creatures we are, we often imagine some sudden critical change, a bit like when the black monolith appears in the film 2001: A Space Odyssey. In reality, there is no evidence of a big change in our biological makeup when we started behaving in an intelligent way. Our model can explain this even if our mental capacities are the same today as they were when we first originated as a species some 200,000 years ago.

"Ironically, our finding that successful innovation depends less on how smart you are than how connected you are seems as relevant today as it was 90,000 years ago.

Eurekalert 17/06/09

New 'molecular clock' aids dating of human migration history

Researchers at the University of Leeds have devised a more accurate method of dating ancient human migration – even when no corroborating archaeological evidence exists.

Estimating the chronology of population migrations throughout mankind's early history has always been problematic. The most widely used genetic method works back to find the last common ancestor of any particular set of lineages using samples of mitochondrial DNA (mtDNA), but this method has recently been shown to be unreliable, throwing 20 years of research into doubt.

The new method refines the mtDNA calculation by taking into account the process of natural selection - which researchers realised was skewing their results - and has been tested successfully against known colonisation dates confirmed by archaeological evidence, such as in Polynesia in the Pacific (approximately 3,000 years ago), and the Canary Islands (approximately 2,500 years ago).

Says PhD student Pedro Soares who devised the new method: "Natural selection's very gradual removal of harmful gene mutations in the mtDNA produces a time-dependent effect on how many mutations you see in the family tree. What we've done is work out a formula that corrects this effect so that we now have a reliable way of dating genetic lineages.

"This means that we can put a timescale on any part of the particular family tree, right back to humanity's last common maternal ancestor, known as 'Mitochondrial Eve', who lived some 200,000 years ago. In fact we can date any migration for which we have available data," he says.

Moreover, working with a published database of more than 2,000 fully sequenced mtDNA samples, Soares' calculation, for the first time, uses data from the whole of the mtDNA molecule. This means that the results are not only more accurate, but also more precise, giving narrower date ranges.

The new method has already yielded some surprising findings. Says archaogeneticist Professor Martin Richards, who supervised Soares: "We can settle the debate regarding mankind's expansion through the Americas. Researchers have been estimating dates from mtDNA that are too old for the archaeological evidence, but our calculations confirm the date to be some 15,000 years ago, around the time of the first unequivocal archaeological remains.

"Furthermore, we can say with some confidence that the estimate of humanity's 'out of Africa' migration was around 60-70,000 years ago – some 10-20,000 years earlier than previously thought."

The team has devised a simple calculator into which researchers can feed their data and this is being made freely available on the University of Leeds website.

Eurekalert 17/06/09

Archaeological discovery in Jordan valley: Enormous 'foot-shaped' enclosures

'The 'foot' structures that we found in the Jordan valley are the first sites that the People of Israel built upon entering Canaan and they testify to the biblical concept of ownership of the land with the foot'.

"The 'foot' structures that we found in the Jordan valley are the first sites that the People of Israel built upon entering Canaan and they testify to the biblical concept of ownership of the land with the foot," said archaeologist Prof. Adam Zertal of the University of Haifa, who headed the excavating team that exposed five compounds in the shape of an enormous "foot", that it were likely to have been used at that time to mark ownership of territory.
On the eve of the Passover holiday, researchers from the University of Haifa reveal an exceptional and exciting archaeological discovery that dates back to the time of the People of Israel's settlement in the country: For the first time, enclosed sites identified with the biblical sites termed in Hebrew "gilgal", which were used for assemblies, preparation for battle, and rituals, have been revealed in the Jordan valley. The researchers, headed by Prof. Adam Zertal, exposed five such structures, each in the shape of an enormous "foot", which they suppose functioned during that period to mark ownership on the territory. "I am an archaeologist and only deal with the scientific findings, so I do not go into the additional meanings of the discovery, if there are any," Prof. Zertal said.
The Hebrew word "gilgal" (a camp or stone-structure), is mentioned thirty-nine times in the Bible. The stone enclosures were located in the Jordan valley and the hill country west of it. To this day, no archaeological site has been proposed to be identified with the gilgal. Between the years 1990 and 2008, during the Manasseh Hill-Country Survey that covers Samaria and the Jordan Valley, five such enclosures were found and excavated, all designed in the shape of a human foot. All of these sites were established at the outset of the Iron Age I (the 13th-12th centuries BCE). Based on their size and shape, it is clear that they were used for human assembly and not for animals.
Two of the sites (in Bedhat esh-Sha'ab and Yafit 3) were excavated in the years 2002-2005, under the directorship of Dr. Ben-Yosef and the guidance of Adam Zertal. The findings, mostly of clay vessels and animal bones, date their foundation to the end of the 13th century BCE, and one of them endured up to the 9th or 8th century BCE without architectonic adjustment.
In at least two cases, paved circuits, some two meters wide, were found around the structures. These were probably used to encircle the sites in a ceremony. "Ceremonial encirclement of an area in procession is an important element in the ancient Near East," Prof. Zertal says, adding that the origins of the Hebrew term "hag" (festival) in Semitic languages is from the verb "hug", which means "encircle". Thus, this discovery can also shed new light on the religious processions and the meaning of the Hebrew word for festival, "hag".
Prof. Zertal emphasized that the "foot" held much significance as a symbol of ownership of territory, control over an enemy, connection between people and land, and presence of the Deity. Some of these concepts are mentioned in ancient Egyptian literature. The Bible also has a wealth of references to the importance of the "foot" as a symbol: of ownership over Canaan, the bond between the People of Israel and their land, the link between the People and God's promise to inherit the land, defeating the enemy 'underfoot', and the Temple imaged as a foot.
"The discovery of these 'foot' structures opens an entirely new system of linguistic and historical perceptions," Prof. Zertal emphasizes. He explains that the meaning of the biblical Hebrew word for "foot" - "regel" – is also a "festival", "holiday", and ascending to see the face of God. As such, the source of the Hebrew term "aliya la-regel", literally translated as "ascending to the foot" (and now known in English as a pilgrimage), is attributed to the "foot" sites in the Jordan valley. "Now, following these discoveries, the meanings of the terms become clear. Identifying the 'foot' enclosures as ancient Israeli ceremonial sites leads us to a series of new possibilities to explain the beginnings of Israel, of the People of Israel's festivals and holidays," he stated.
According to Prof. Zertal, the "foot" constructions were used for ceremonial assemblies during Iron Age I (and probably after). When the religious center was moved to Jerusalem and settled there, the command of "aliya la-regel" (pilgrimage) became associated with Jerusalem. The source of the term, however, is in the sites that have now been discovered in the Jordan valley and the Altar on Mt. Ebal. "The biblical text testifies to the antiquity of these compounds in Israel's ceremonials, and the 'foot' structures were built by an organized community that had a central leadership," Prof. Zertal stated. He stressed that there is a direct connection between the biblical ideology, which identifies ownership over the new land with the foot and hence with the shape of the constructions.

Source:Eurekalert 6th April 2009.

1.5 million-year-old fossil humans walked on modern feet

Image courtesy Matthew Bennett, Bournemouth University

Footprints found at Ileret, Kenya, display anatomically modern features.





Ancient footprints found at Rutgers' Koobi Fora Field School show that some of the earliest humans walked like us and did so on anatomically modern feet 1.5 million years ago.
Published as the cover story in the Feb. 27 issue of the journal Science, this anatomical interpretation is the conclusion of Rutgers Professor John W.K. Harris and an international team of colleagues. Harris is a professor of anthropology at Rutgers, The State University of New Jersey, member of the Center for Human Evolutionary Studies and director of the Koobi Fora Field Project.
Harris is also director of the field school which Rutgers University operates in collaboration with the National Museums of Kenya. From 2006 to 2008, the field school group of mostly American undergraduates, including Rutgers students, excavated the site yielding the footprints.
The footprints were discovered in two 1.5 million-year-old sedimentary layers near Ileret in northern Kenya. These rarest of impressions yielded information about soft tissue form and structure not normally accessible in fossilized bones. The Ileret footprints constitute the oldest evidence of an essentially modern human-like foot anatomy.
To ensure that comparisons made with modern human and other fossil hominid footprints were objective, the Ileret footprints were scanned and digitized by the lead author, Professor Matthew Bennett of Bournemouth University in the United Kingdom.
The authors of the Science paper reported that the upper sediment layer contained three footprint trails: two trails of two prints each, one of seven prints and a number of isolated prints. Five meters deeper, the other sediment surface preserved one trail of two prints and a single isolated smaller print, probably from a juvenile.
In these specimens, the big toe is parallel to the other toes, unlike that of apes where it is separated in a grasping configuration useful in the trees. The footprints show a pronounced human-like arch and short toes, typically associated with an upright bipedal stance. The size, spacing and depth of the impressions were the basis of estimates of weight, stride and gait, all found to be within the range of modern humans.
Based on size of the footprints and their modern anatomical characteristics, the authors attribute the prints to the hominid Homo ergaster, or early Homo erectus as it is more generally known. This was the first hominid to have had the same body proportions (longer legs and shorter arms) as modern Homo sapiens. Various H. ergaster or H. erectus remains have been found in Tanzania, Ethiopia, Kenya and South Africa, with dates consistent with the Ileret footprints.
Other hominid fossil footprints dating to 3.6 million years ago had been discovered in 1978 by Mary Leakey at Laetoli, Tanzania. These are attributed to the less advanced Australopithecus afarensis, a possible ancestral hominid. The smaller, older Laetoli prints show indications of upright bipedal posture but possess a shallower arch and a more ape-like, divergent big toe.

Source: Eurekalert 28/02/09

Arsenic and old toenails

Scientists from Leicester and Nottingham have devised a method for identifying levels of exposure to environmental arsenic – by testing toenail clippings.

Arsenic occurs naturally in the environment and people can be exposed to it in several ways, for example through contaminated water, food, dust or soil. The risk of exposure is greater in certain areas of the UK where the natural geology and historic mining activities have led to widespread contamination of the environment with arsenic. Long term exposure to arsenic is associated with increases in lung, liver, bladder and kidney cancers and skin growths.

Previous studies using hair have suggested high levels of arsenic in the bodies of King George III and Napoleon Bonaparte. Now doctoral research at the British Geological Survey by Mark Button of the University of Leicester has used toenail clippings to find fresh evidence of exposure to environmental arsenic within a UK population living close to a former arsenic mine. The research, published online ahead of print in the Journal of Environmental Monitoring, was carried out with Dr Gawen Jenkin, Department of Geology, University of Leicester; Dr Chris Harrington, School of Science and Technology at Nottingham Trent University and Dr Michael Watts of the British Geological Survey. The research was funded by the British Geological Survey.

Mark Button said "We initially identified high levels of arsenic in earthworms living in contaminated soils surrounding the former mine. That got us thinking about potential exposure in people living close to the site."

The researchers collected toenails and washed and acid digested the samples under microwave irradiation. They then analysed the samples using inductively coupled plasma mass spectrometry.

Mark Button added: "This preliminary research indicates that people living close to a former arsenic mine have elevated levels of arsenic in their toenails. However, the potential health risks in this case, if any, are not yet clear and no arsenic related health issues have been reported. A large-scale and more detailed biomonitoring study is required to confirm these initial results."

Dr Jenkin, lecturer in Applied Geology at the University of Leicester said: "This is the first time that the chemical form of the arsenic in the toenails has been measured – that can tell us something about how it got in there and possible risk factors.

Dr Jenkin added: "There is definitely more research needed to look at - amongst other things - a larger sample of volunteers, to see if the values change with time (it is quite possible the high values recorded are a one-off for that person, or due to slow toenail growth concentrating harmless quantities of arsenic), and to look at the possible pathways by which the arsenic is ingested. Coupling our analyses with regular blood measurements would be very revealing."

However the researchers are definitely NOT requiring people to send in their toenail clippings. Neither can you assess arsenic contamination simply by looking at your toenails.

Dr Jenkin said: "Even in those people with elevated amounts it is present in tiny quantities – less than 0.003% in the toenail. In people who have not been exposed at all it is less than 0.00003%. If a nail looks different from normal that is usually due to physical damage (you stubbed your toe or dropped something on it) or a minor fungal infection that can be easily cleared up by a visit to the podiatrist."

Source: Eurekalert 23/02/09

Bipedality and Childbirth.

Contrary to the TV sitcom where the wife experiencing strong labor pains screams at her husband to stay away from her, women rarely give birth alone. There are typically doctors, nurses and husbands in hospital delivery rooms, and sometimes even other relatives and friends. Midwives often are called on to help with births at home.


Assisted birth has likely been around for millennia, possibly dating as far back as 5million years ago when our ancestors first began walking upright, according to University of Delaware paleoanthropologist Karen Rosenberg.
She says that social assistance during childbirth is just one aspect of our evolutionary heritage that makes us distinctive as humans.
Rosenberg, who is a professor and chairperson of the Department of Anthropology at the University of Delaware, presented a talk on natural selection and childbirth on Feb. 13 at the annual meeting of the American Association for the Advancement of Science in Chicago. It was part of the symposium “The Invisible Woman in Evolution: Natural Cycle and Life-Cycle Events,” which Rosenberg co-organized.
The meeting's theme, “Our Planet and Its Life: Origins and Futures,” commemorated the 200th anniversary of Charles Darwin's birth and the 150th anniversary of the publication of his book On the Origin of Species by Means of Natural Selection.
“Humans need helpers in childbirth because it is difficult and potentially dangerous,” Rosenberg says. “While it's not so risky today -- maternal mortality is low -- as recently as two generations ago, it was not uncommon to hear of women dying in childbirth.”
Through fossil records and comparisons of humans with other primates, Rosenberg says that anthropologists can now show how the uniquely human traits of bipedalism, large brains, infant helplessness and social assistance all came together, resulting in the challenging and somewhat dangerous manner in which humans give birth.
When our ancestors evolved to begin walking on two legs, Rosenberg says, this upright posture created a wide but short opening in the pelvis in which the baby must travel, requiring a new form of birth so that the baby could find its way through a now tight birth canal.
According to Rosenberg, the average pelvic opening in women today is 13 centimeters at its largest diameter and 10 centimeters at its smallest. The average infant head is 10 centimeters from front to back, and the shoulders are 12 centimeters across. And today the birth canal is a twisty tunnel subjecting the infant to a series of complex twists and turns on its way out.
“Until recently, there was a sexism in the study of evolution,” Rosenberg says. “Researchers focused on men and the tools they used in hunting, and these things were more difficult to connect to reproductive success and hence to natural selection,” she notes.
“With childbirth, as well as many of the other things that happen to women -- pregnancy, nursing, menopause -- it's really easy to see how natural selection works,” Rosenberg notes.
Childbirth is just one of a series of examples throughout a woman's life cycle, in which enlisting the help of other women significantly improves reproductive outcomes, according to Rosenberg.
“Women take up the slack for other women when they are pregnant and nursing so that they have the energy to devote to their infants. Cooperative childcare is something in which women help each other out. Often, but not always, these helpers are post-reproductive women who have fewer of those responsibilities of their own, but may be helping out their daughters. All of this puts a great selective premium on a kind of social intelligence that many scientists think partly accounts for the increase in brain size that happened over the last two million years,” she notes.
How will women and childbirth continue to evolve? Will the birth canal grow narrower, or wider? Will childbirth become more painful, or easier? Will more helpers be needed in future births? It's really anybody's guess.
“Evolution doesn't have a direction,” Rosenberg says. “Knowing where we've been doesn't give us any help in where we're going. But it does help us understand what makes us human, as well as how we're connected to the natural world. ”
A graduate of the University of Chicago, Rosenberg received her doctorate in biological anthropology from the University of Michigan and joined the University of Delaware faculty in 1987.
She says she began focusing on the evolution of women and childbirth around the time she had her first child, although she doesn't think there was a connection between the two.
Ironically, her brother is an obstetrician although she and he have never conducted research together.

Source:Eurekalert 02/09
Article by Tracey Bryant. Photo by Ambre Alexander

High-tech tests allow anthropologists to track ancient hominids across the landscape.

Caption: This is an an artist's representation of Paranthropus in southern Africa more than 1 million years ago.
Credit: Illustration courtesy of Walter Voigt/Lee Berger/Brett Hilton-Barber.

Dazzling new scientific techniques are allowing archaeologists to track the movements and menus of extinct hominids through the seasons and years as they ate their way across the African landscape, helping to illuminate the evolution of human diets.
Piecing together relationships between the diets of hominids several million years ago to that of early and modern humans is allowing scientists to see how diet relates to the evolution of cognitive abilities, social structures, locomotion and even disease, said University of Colorado at Boulder anthropology Professor Matt Sponheimer. Sponheimer organized a session titled "The Evolution of Human Diets" at the annual American Association for the Advancement of Science meeting Feb. 12-15 in Chicago.
Sponheimer specializes in stable isotope analysis, comparing particular forms of the same chemical element, like carbon, present in fossil remains to help reconstruct past lives of hominids. Zapping hominid teeth with lasers, for example, frees telltale carbon gases from the enamel, allowing scientists to pinpoint the types of plants consumed by the hominids and the environments where they lived, said Sponheimer, who also relies on the microscopic wear of ancient hominid teeth for data on food consumption.
"Darwin surmised more than 150 years ago in 'The Descent of Man' that changes in the subsistence or environment of human ancestors likely led to the advent of modern humans," Sponheimer said. "Dietary resources can be a force for evolution."
One hominid genus under study by Sponheimer is the 2 million-year-old Paranthropus, a short, upright member of the australopithecine family that includes the Ethiopian fossil, Lucy. Discovered in 1974, Lucy, believed to be roughly 3 million years old, is regarded by many anthropologists as the matriarch of modern humans.
A 2006 study by Sponheimer of Paranthropus robustus documented its diverse diet, clouding the notion that it was driven to extinction by its picky eating habits. And a 1999 study led by Sponheimer indicated 3-million-year-old australopithecines may have even have been catching and eating small animals.
"Paranthropus is sometimes referred to as a nutcracker because its flat teeth and powerful jaw muscles appear designed to eat hard foods," he said. "But some research suggests that the most mechanically challenging foods like nuts were eaten only at limited times of the year. "In addition, foods not previously considered to have been consumed in significant quantities, like sedges, grasses, seeds and perhaps even animal foods, were a significant part of the Paranthropus diet."
Roughly 2.5 million years ago, the australopithicenes are thought to have split into the genus Homo and the now-extinct genus Paranthropus, including South Africa's Paranthropus robustus and East Africa's Paranthropus boisei, said Sponheimer. Research presently under way at CU-Boulder indicates that while Paranthropus robustus and Paranthropus boisei are almost indistinguishable anatomically, they may have had very different diets.
Other intriguing research under way by Sponheimer and his colleagues hints that some female australopithecines, including members of the Paranthropus genus, died in different geographic areas than where they were born. The researchers are comparing such data to social patterns of chimpanzees, in which females generally migrate away from their original ranges and move into new areas -- the opposite of behavior charted in most other primates, said Sponheimer.
"Textbooks treat these ancient hominids as static piles of fossil bones," said Sponheimer. "We treat them as biological organisms moving across the landscape. It's entirely possible that many things we thought we knew about them were wrong, and pages of textbooks will have to have to be re-written."