Wednesday, January 28, 2015
The discovery of a 55,000-year-old partial skull in Northern Israel provides new insights into the migration of modern humans out of Africa. The rare find is reported in the journal Nature this week by an international team of Israeli, North American and European researchers.
A key event in human evolution was the expansion of modern humans of African origin across Eurasia, replacing all other forms of hominin (humans and their predecessors), around 40,000-60,000 years ago. However, due to the scarcity of human fossils from this period, these ancestors of all present-day non-African modern populations have largely remained a mystery.
Now, researchers describe a partial skull that dates to around 55,000, which was found at Manot Cave in Israel's Western Galilee. The skull has a distinctive "bun"-shaped occipital region at the back. In this way its shape resembles modern African and European skulls, but differs from other anatomically modern humans from the Levant. This suggests that the Manot people could be closely related to the first modern humans that later colonized Europe.
The specimen also provides evidence that both modern humans and Neanderthals inhabited the southern Levant during the late Pleistocene, close in time to the likely interbreeding event between modern humans and Neanderthals.
This finding represents the first fossil evidence from the critical period when genetic and archaeological models predict that African modern humans successfully migrated out of Africa and colonized Eurasia. It also represents the first fossil evidence that during the late Middle Paleolithic, the Levant was occupied not only by Neanderthals but also by modern humans.
The researchers suggest that the population from which this skull is derived had recently migrated out of Africa and established itself in the Levantine corridor during a time span that was favorable for human migration, due to warmer and wetter climatic events over the Northern Sahara and the Mediterranean.
Manot is a karstic cave in the North of Israel, very close to the Lebanese border. The first excavations began in 2010 and are continued up to day. Countless archaeological objects were discovered which document the peopling of the cave since more than 100,000 years. Around 30,000 years ago, the roof of the cave collapsed and sealed the archaeological layers until the 21st century. Beside stone tools and animal bones, some few human remains were preserved. The most spectacular finding was made on an elevated shelf within a small chamber of the cave: a very well preserved "calotte", hence the upper part of a braincase. The facial bones which contain a lot of diagnostic traits for paleoanthropologists, were, however, missing.
"Virtual Anthropology" allows identification
The traditional methods of anthropology permit to draw only a coarse picture with regard to classification if it comes to a partial braincase which features mainly smooth curvatures. By means of methods that were developed at the University of Vienna in the last 15 years it is now possible to come to much stronger statements. This "Virtual Anthropology" uses sophisticated mathematical-statistical procedures to analyse 3D data from objects. Professor Gerhard Weber from the Department of Anthropology at the University of Vienna was thus invited by the Israeli colleagues to participate. Together with his former Ph.D. student Dr. Philipp Gunz, who now works at the Max Planck Institute Leipzig, they examined carefully computer-tomographic images of the calotte. In doing so, numerous measuring points in a dense array were located on the virtual representation of Manot and on several hundreds of other braincases to capture differences and similarities. Weber states: "The shape analysis shows very clearly that Manot was a modern human. It is interesting that the most similar skulls in our sample come from recent Africans on the one hand, and on the other hand from those modern humans that lived in Europe between 20-30,000 years ago as, for instance, Mlade? 1 or P?edmostí 4 from the Czech Republic".
Absolute dating proves old age
The morphological results alone would be, however, not enough for a sensation. The Manot people could have been modern humans that later re-migrated from Europe back into the Levant. Luckily, the conditions in the flowstone-cave lead to the accumulation of several thin layers of calcite on the inner and outer surface of the skull fragment. These can be reliably dated with the uranium-thorium method. The Israeli colleagues documented an age of approximately 55,000 years. Manot is thus 10,000 years older than any modern human found in Europe, and about 5-10,000 years younger than the point when geneticists predict the appearance of our direct ancestors in Africa.
The Levant as crossing point of migration
One of the logical migration routes from Africa to Europe leads through the Levantine corridor. The age and the morphology of Manot suggest that the first modern humans took this route. At the same time, they had opportunity to meet Neandertals which occupied the Levant in this time but could never expand further south. Genetic results indicate that recent humans carry between 1-4% of Neandertal genes in their genome. So far it was speculated that admixture could have happened in Europe. Manot is changing this picture. It is likely that interbreeding happened already earlier on the way of the first modern humans through the Levant.
"This skull remain at Manot", Weber summarises "is exactly what we anthropologists have looked for since decades. It connects perfectly in space and time those separated parts of human history that we have known". But Manot is not only a fluke for our knowledge about human evolution. It also lead to a very successful scientific collaboration between Israeli and Austrian, respectively German, institutions. Further projects and increased exchange of know-how are on the way.
Archaeologists continue to debate the reasons for the collapse of many Central American cities and states, from Teotihuacan in Mexico to the Yucatan Maya, and climate change is considered one of the major causes.
A University of California, Berkeley, study sheds new light on this question, providing evidence that a prolonged period of below-average rainfall was partly responsible for the abandonment of one such city, Cantona, between A.D. 900 and A.D. 1050.
At its peak, Cantona, located in a dry, volcanic basin (La Cuenca Oriental) east of today's Mexico City, was one of the largest cities in the New World, with 90,000 inhabitants. The area was a major source of obsidian and the city may have played a military role alongside an important trade route from the Veracruz coast into the highlands.
To assess the climate in that area before and after Cantona's collapse, UC Berkeley geographers analyzed sediment cores from a lake located 20 miles south of the former city. They found evidence of a 650-year period of frequent droughts that extended from around A.D. 500 to about A.D. 1150. This was part of a long-term drying trend in highland Mexico that started 2,200 years ago, around 200 B.C. The climate became wetter again in about A.D. 1300, just prior to the rise of the Aztec empire.
"The decline of Cantona occurred during this dry interval, and we conclude that climate change probably played a role, at least towards the end of the city's existence," said lead author Tripti Bhattacharya, a UC Berkeley graduate student.
Surprisingly, the population of Cantona increased during the early part of the dry period, perhaps because of political upheaval elsewhere that increased the importance of the heavily fortified city, she said. Teotihuacan, less than 100 miles to the west, was in decline at the time, also possibly because of more frequent droughts.
"In a sense the area became important because of the increased frequency of drought," said UC Berkeley associate professor of geography Roger Byrne. "But when the droughts continued on such a scale, the subsistence base for the whole area changed and people just had to leave. The city was abandoned."
Bhattacharya, Byrne and their colleagues report their findings in an article appearing this week in the early edition of the journal Proceedings of the National Academy of Sciences. The UC Berkeley researchers analyzed lake cores provided by scientists at the National Autonomous University of Mexico in Juriquilla, Querétaro, Mexico and the German Research Centre for Geosciences in Potsdam, Germany.
Political upheaval and climate change
Byrne emphasized that the area's typical monsoon weather with wet summers and dry winters did not stop, but was interrupted by frequent short-term droughts, no doubt affecting crops and water supplies. Today the area is close to the northern limit of maize production without irrigation, and would have been particularly vulnerable to drier conditions, he said.
Byrne, a member of the Berkeley Initiative on Global Change Biology (BiGCB) and curator of fossil pollen in the Museum of Paleontology, has studied sediment cores from many lakes in Mexico and California, and is particularly interested in possible links between climate change and human activities.
Nearly 20 years ago, he learned of Cantona and traveled with students to the areas three times to obtain cores from lakes near the site, most of which are maar lakes created by magma explosions. They are deep and often contain undisturbed and regularly layered sediments ideal for chronological studies.
German colleagues cored this particular lake, Aljojuca, in 2007, and Bhattacharya traveled to Potsdam to collect sediment samples. Oxygen isotope ratios in carbonate sediments are correlated with the ratio of precipitation to evaporation and thus indicate aridity. Organic material in the sediments was used for accelerator mass spectroscopy carbon-14 dating.
"We can show that both the growth and decline of the site took place during a time period of frequent drought, which forces us to think in more nuanced ways about how political and social factors interact with environmental factors to cause social and cultural change," Bhattacharya said. "That makes the study particularly interesting."
Bhattacharya noted that more studies are necessary to reconstruct the prehistoric climate of highland Mexico. Such studies could reveal the causes of prehistoric climatic change and whether they were similar to the factors that regulate the region's climate today, such as the El Niño/Southern Oscillation.
Saturday, January 17, 2015
New research from the University of Bristol, UK has revealed the antiquity of dairy farming in a region famous for its dairy exports: Ireland.
Research published today in the Journal of Environmental Archaeology shows that dairying on the island goes back approximately 6,000 years, revealed through traces of ancient dairy fats found in pots dating to around 4,000 to 2,500 BC.
Dr Jessica Smyth of Bristol's School of Chemistry analysed nearly 500 pots from the Neolithic, the period when people switched from hunting and gathering to farming. In Britain and Ireland, this change occurred around 4,000 BC, more than 1,000 years later than on the Continent. The Bristol team use a combination of fat or lipid 'fingerprinting' and compound-specific carbon isotope techniques to identify the origin of fats preserved in the walls of prehistoric cooking pots.
Dr Smyth, who led the study, said: "We know from previous research that dairying was an important part of many early farming economies, but what was a big surprise was the prevalence of dairy residues in Irish pots. It looks to have been a very important food source."
Ninety per cent of the residues tested for fat origin were found to be dairy fats, with ten per cent found to be meat fats (beef or mutton) or a mixture of milk and meat.
Dr Smyth added: "People can obviously cook meat in other ways than boiling it in pots, and there is plenty of evidence for cereal processing at this time, but the Irish dairy signal remains very striking, particularly when you compare it with the continental European data sets. Ireland really does seem to go mad for milk in the Neolithic."
Milk is still a traditional and valuable food in Europe today, produced by over 30 million dairy cows and representing 14 per cent of the value of European agricultural production [2011 figures]. Six thousand years ago, dairying in Ireland looked very different.
Dr Smyth said: "We know that settlements were small in the Irish Neolithic, usually one or two houses, so it's likely that early farming groups had just one or two animals supporting the household with their products, which were perhaps part of a wider community herd."
Such results are even more significant given the fact that domesticated animals such as cattle, sheep and goats had to be physically shipped to Ireland as part of the process, as these animals were not native to the island.
"These are a very determined group of pioneer farmers. They are setting up everything from scratch, and taking a significant gamble with their livelihoods and those of their dependants," Dr Smyth said.
It would appear that the Irish love of dairy products is very ancient, and the suitability of the island for dairy farming was recognised early in prehistory.