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Freeze 'condemned Neanderthals'

Submitted by coldrum on Monday, 26 February 2007  Page Views: 6945

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A sharp freeze could have dealt the killer blow that finished off our evolutionary cousins the Neanderthals, according to a new study.

The ancient humans are thought to have died out in most parts of Europe by about 35,000 years ago.

And now new data from their last known refuge in southern Iberia indicates the final population was probably beaten by a cold spell some 24,000 years ago.

The research is reported by experts from the Gibraltar Museum and Spain.

They say a climate downturn may have caused a drought, placing pressure on the last surviving Neanderthals by reducing their supplies of fresh water and killing off the animals they hunted.

Sediment cores drilled from the sea bed near the Balearic Islands show the average sea-surface temperature plunged to 8C (46F). Modern-day sea surface temperatures in the same region vary from 14C (57F) to 20C (68F).

In addition, increased amounts of sand were deposited in the sea and the amount of river water running into the sea also plummeted.

Southern refuge

Neanderthals appear in the fossil record about 350,000 years ago and, at their peak, these squat, physically powerful hunters dominated a wide range, spanning Britain and Iberia in the west to Israel in the south and Uzbekistan in the east.

Our own species, Homo sapiens, evolved in Africa, and displaced the Neanderthals after entering Europe about 40,000 years ago.

During the last Ice Age, the Iberian Peninsula was a refuge where Neanderthals lived on for several thousand years after they had died out elsewhere in Europe.

These creatures (Homo neanderthalensis) had survived in local pockets during previous Ice Ages, bouncing back when conditions improved. But the last one appears to have been characterised by several rapid and severe changes in climate which hit a peak 30,000 years ago.

Southern Iberia appears to have been sheltered from the worst of these. But about 24,000 years ago, conditions did deteriorate there.

This event was the most severe the region had seen for 250,000 years, report Clive Finlayson, from the Gibraltar Museum; Francisco Jimenez-Espejo, from the University of Granada, Spain; and colleagues.

Their findings are published in the journal Quaternary Science Reviews.

Rare event

"It looks pretty severe and also quite short," Professor Finlayson told BBC News.

"Things like olive trees and oak trees that are still with us today managed to ride it out. But a very fragmented, stressed population of Neanderthals - and perhaps other elements of the fauna - did not."

The cause of this chill may have been cyclical changes in the Earth's position relative to the Sun - so-called Milankovitch cycles.

But a rare combination of freezing polar air blowing down the Rhone valley and Saharan air blowing north seems to have helped cool this part of the Mediterranean Sea, contributing to the severe conditions.

Gorham's Cave on Gibraltar shows evidence of occupation by groups of Neanderthals until 24,000 years ago. But thereafter, researchers have found no signs of their presence.

However, in an interesting new development, scientists are also now reporting another site, from south-east Spain, which has yielded evidence for the late survival of Neanderthals.

In a study published in the journal Geobios, Jose Carrion, Santiago Fernandez Jimenez, from the University of Murcia; and colleagues analysed pollen from soil layers at Carihuela cave to determine how vegetation had changed in the area during the past 15,000 years.

During the course of this work, they also obtained ages for sediment samples from the cave, using radiocarbon dating and uranium-thorium dating.

Sediment layers containing Neanderthal tools were found to date from 45,000 years ago until 21,000 years ago.

Caution needed

These radiocarbon dates are "raw", and do not exactly correspond to calendar dates. They cannot therefore be compared directly with those from Gibraltar, which have been calibrated with calendar dates.

Neanderthal bones have also been excavated from these sediment units, including a male skull fragment which could potentially be very recent. But Professor Carrion is extremely reluctant to draw conclusions about these human remains.

Spanish archaeologists carried out a detailed excavation of Carihuela between 1979 and 1992. But the cave is currently closed due to a dispute between national and regional governments over rights to dig at the cave.

"The human bones have been recovered in different excavation campaigns over 50 years. The relationship between them and the dates I provide must be treated with caution," Professor Carrion told BBC News.

He added that sediments in parts of the cave could have been churned up, mixing old bones in with younger material. He suggested Carihuela should be re-excavated to resolve some of the controversies surrounding the site.

Clive Finlayson suggested the late Neanderthal dates from Carihuela might agree well with those from Gibraltar once they were calibrated.

bbc.co.uk.
Contributor Bio for coldrum: Based in Milkyway, contributing since 2002. Favourite site: Avebury.

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"Freeze 'condemned Neanderthals'" | Login/Create an Account | 5 News and Comments
  
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Competition, Not Climate Change, Led To Neanderthal Extinction, Study Shows by coldrum on Friday, 30 January 2009
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Competition, Not Climate Change, Led To Neanderthal Extinction, Study Shows

In a recently conducted study, a multidisciplinary French-American research team with expertise in archaeology, past climates, and ecology reported that Neanderthal extinction was principally a result of competition with Cro-Magnon populations, rather than the consequences of climate change.


The study, reported in the online, open-access journal PLoS ONE on December 24, figures in the ongoing debate on the reasons behind the eventual disappearance of Neanderthal populations, which occupied Europe prior to the arrival of human populations like us around 40,000 years ago. Led by Dr William E. Banks, the authors, who belong to the French Centre National de la Recherche Scientifique, l'Ecole Pratique d'Hautes Etudes, and the University of Kansas, reached their conclusion by reconstructing climatic conditions during this period and analyzing the distribution of archaeological sites associated with the last Neanderthals and the first modern human populations with an approach typically used to study the impact of climate change on biodiversity.

This method uses geographic locations of archaeological sites dated by radiocarbon, in conjunction with high-resolution simulations of past climates for specific periods, and employs an algorithm to analyze relationships between the two datasets to reconstruct potential areas occupied by each human population and to determine if and how climatic conditions played a role in shaping these areas. In other words, by integrating archaeological and paleoenvironmental datasets, this predictive method can reconstruct the regions that a past population could potentially have occupied. By repeating the modeling process hundreds of times and evaluating where the errors occur, this machine-learning algorithm is able to provide robust predictions of regions that could have been occupied by specific human cultures.

This modeling approach also allows the projection of the ecological footprint of one culture onto the environmental conditions of a later climatic phase―by comparing this projected prediction to the known archaeological sites dated to this later period, it is possible to determine if the ecological niche exploited by this human population remained the same, or if it contracted or expanded during that period of time.

Comparing these reconstructed areas for Neanderthals and anatomically modern humans during each of the climatic phases concerned, and by projecting each niche onto the subsequent climatic phases, Banks and colleagues determined that Neanderthals had the possibility to maintain their range across Europe during a period of less severe climatic conditions called Greenland Interstadial 8 (GI8).

However, the archaeological record shows that this did not occur, and Neanderthal disappearance occurs at a point when we see the geographic expansion of the ecological niche occupied by modern humans during GI8. The researchers' models predict the southern limit of the modern human territory to be near the Ebro River Valley in northern Spain during the preceding cold period called Heinrich Event 4 (H4), and that this southern boundary moved to the south during the more temperate phase GI8.

The researchers conclude that the Neanderthal populations that occupied what is now southern Spain were the last to survive because they were able to avoid direct competition with modern humans since the two populations exploited distinct territories during the cold climatic conditions of H4. They also point out that during this population event contact between Neanderthals and modern humans may have permitted cultural and genetic exchanges.

http://www.sciencedaily.com/releases/2008/12/081229105039.htm
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Early Human Ancestors May Have Had Harems by coldrum on Tuesday, 18 December 2007
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Early Human Ancestors May Have Had

Some early human ancestors may have lived in "harem" societies much like those of modern gorillas and orangutans, a new fossil study suggests.

Such an arrangement is known to arise in some modern primate species when males mature later in life than females and become much larger than their mates.

In these cases a single dominant male mates with and protects a large harem of females.

The new find is based on analysis of fossils from the human relative Paranthropus robustus.

The primate species, which lived in Africa about 2 million to 1.2 million years ago, is closely related to early humans but is a dead-end branch of the family tree.

P. robustus is a descendant of Australopithecus afarensis, the species that also gave rise to the Homo genus that includes modern humans.

Charles Lockwood, an anthropologist at University College London, and colleagues looked at roughly three dozen fossil skulls and teeth from P. robustus.

Telltale traits of the fossils showed that male members of the species matured late in life.

This led Lockwood to theorize that P. robustus males competed for groups of mates much the way gorillas do today.

The findings appear this week in the journal Science.

Size Matters

Male gorillas and orangutans grow significantly in adulthood and tend to become dramatically larger than females of their species.

"Orangutans are the most extreme situation," Lockwood said.

"Male orangutans go through an amazing transformation. They put on a lot of weight and get flanges on the sides of their faces. They appear nearly twice their old size, though some of that is an illusion and the change in the skeleton is much more subtle."

Adult males can stand 5 feet (1.5 meters) tall and weigh more than 200 pounds (90 kilograms), while females reach about 3.5 feet (a meter) tall and weigh in around 110 pounds (50 kilograms).

Such extreme size differences aren't common in other primates such as chimpanzees or humans—species in which harem mating behavior is abnormal.

Among humans, a single dominant male ruling a bevy of mates may seem to be a lucky individual. But the reproductive strategy was actually quite hazardous, scientists say.

The P. robustus fossils, found at the Cradle of Humankind World Heritage site in South Africa, are predominantly those deposited by ancient predators such as leopards and hyenas.

Because the remains are mostly male, they appear to have become victims far more often than females.

"Basically, males had a high-risk, high-return lifestyle in this species," Lockwood said.

"They most likely left their birth groups at about the time they reached maturity, and it was a long time before they were mature enough to attract females and establish a new group.

"Some of them were killed by predators before they got the chance," he added.

"One reason why that's important is because there are so few females in the fossil sample, [so] it appears that they were relatively safe.

"A key inference is that there were stable groups of females that would have allowed males to pursue this [harem] strategy."

Food vs. Females

Richard Potts, director of the Human Origins Program at the Smithsonian Institution's National Museum of Natural History, notes that it's very difficult to reconstruct early human ancestors' sex and social life.

(Related news: "Human, Chimp Ancestors May Have Mated, DNA Suggests" [May 17, 2006].)

"Lockwood's study is very clever in using the fossil record to interpret the pattern of growth in males and females in P. robustus and connecting it to the pattern of male competition, which seems to parallel that of gorillas," Potts said.

He also cited earlier theories that suggested the species may have lived in harem-type groups.

These more speculative ideas centered on the environmental conditions of life on an open savanna.

Widely dispersed plants might have caused males to emphasize defending their proximity to females rather than basing their territories on food sources, the theories say.

"It's intriguing to me that Lockwood and colleagues have come up with anatomical evidence that converges on a similar interpretation about the social lives of Paranthropus," Potts said.

http://news.nationalgeographic.com/news/2007/11/071129-ancient-harem.html
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Climate swings shaped human evolution, researchers claim by coldrum on Tuesday, 18 December 2007
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Climate swings shaped human evolution, researchers claim

The evolution of our earliest human ancestors was driven by wild swings in eastern Africa's ancient climate, scientists claim today.

The rapidly changing climate reshaped the landscape, leaving once plentiful food and water resources in scarce supply and placing enormous pressure on early humans to adapt.

The sustained upheaval drove some species to the brink of extinction, while other better-suited relatives emerged and flourished, the scientists believe.

Researchers identified several extreme shifts in climate dating back millions of years to when humans were first emerging on the continent. Three of the greatest periods of climatic change took place around 2.5m, 1.5m and 1m years ago. These roughly coincide with the appearance of Homo habilis, the first human species; Australopithecus afarensis, a sturdy primitive ape, and the later human species, Homo erectus, which became adept at stone tool use and hunting.

Researchers led by Mark Maslin, director of the Environment Institute at University College London, conducted geological surveys of ancient lakes throughout eastern Africa. They found evidence that over the past 3m years, giant lakes up to 300 metres deep formed and then vanished with the changing climate. The disappearances of the lakes were followed by periods of extreme drought.

"At one extreme, the landscape would have been a true Garden of Eden, with beautiful freshwater lakes, beautiful shorelines and forests along the rivers. There would have been open spaces allowing early humans to exist easily, with water and lots of resources," said Maslin. "But occasionally, these quickly flipped into bone dry periods, where it's 45C in the middle of the day and no natural water resources."

Early humans and other primate species, collectively known as hominids, were forced to adapt to the new environment. Humans developed larger brains, evident in Homo habilis and Homo erectus, enabling them to fashion simple stone cutting tools and form effective hunting groups. Other ancient primates, such as the squat Australopithecus afarensis, emerged with powerful jaws that allowed them to chew and get nutrition from tough roots and vegetables.

"If you look at the new species of hominid that evolved, 80% of those, or 13 out of 15, appeared during these pulsed climate periods. It suggests new human species evolved when the climate was highly variable. We don't know if it's the wet period, the dry period or the transition that triggers this, but we can say that when the climate is highly variable, you get a big change in species."

The research, conducted with scientists at Adelphi University in New York, was published today in the Journal of Human Evolution.

http://www.guardian.co.uk/environment/2007/nov/19/climatechange.evolution
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New evidence on the role of climate in Neanderthal extinction by coldrum on Wednesday, 17 October 2007
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New evidence on the role of climate in Neanderthal extinction

THE mystery of what killed the Neanderthals has moved a step closer to resolution after an international study led by the University of Leeds has ruled out one of the competing theories – catastrophic climate change – as the most likely cause.

The bones of more than 400 Neanderthals have been found since the first discoveries were made in the early 19th century. The finds suggest the Neanderthals, named after the Neander Valley near Düsseldorf, where they were first recognized as an extinct kind of archaic humans, inhabited Europe and parts of western Asia for more than 100,000 years.

The causes of their extinction have puzzled scientists for years – with some believing it was due to competition with modern humans, while others blamed deteriorating climatic conditions. But a new study published today in Nature has shown that the Neanderthal extinction did not coincide with any of the extreme climate events that punctuated the last glacial period.

The research was led by Professor Chronis Tzedakis, a palaeoecologist at the University of Leeds, who explained: “Until now, there have been three limitations to understanding the role of climate in the Neanderthal extinction: uncertainty over the exact timing of their disappearance; uncertainties in converting radiocarbon dates to actual calendar years; and the chronological imprecision of the ancient climate record.”

The team’s novel method – mapping radiocarbon dates of interest directly onto a well-dated palaeoclimate archive – circumvented the last two problems, providing a much more detailed picture of the climate at the possible times of the Neanderthal disappearance.

The researchers applied the new method to three alternative sets of dates for the timing of the Neanderthal extinction from Gorham’s Cave, Gibraltar, a site which is thought to have been occupied by some of the latest surviving Neanderthals:


a set of generally accepted but older dates (around 30-32,000 radiocarbon years ago)
newly-suggested younger dates (around 28,000 radiocarbon years ago)
more contentious dates (around 24,000 radiocarbon years ago).

The team showed that during the first two sets of dates, Europe was experiencing conditions similar to the general climatic instability of the last glacial period – conditions the Neanderthals had already proved able to survive.

The much more controversial date of around 24,000 radiocarbon years ago placed the last Neanderthals just before a large expansion of ice sheets and the onset of cold conditions in northern Europe. “But at that time, Gibraltar’s climate remained relatively unaffected, perhaps as a result of warm water from the subtropical Atlantic entering the western Mediterranean,” explained palaeoceanographer Isabel Cacho of the University of Barcelona.

“Our findings suggest that there was no single climatic event that caused the extinction of the Neanderthals,” concludes palaeonthropologist Katerina Harvati of the Max Planck Institute for Evolutionary Anthropology. “Only the controversial date of 24,000 radiocarbon years for their disappearance, if proven correct, coincides with a major environmental shift. Even in this case, however, the role of climate would have been indirect, by promoting competition with other human groups.”

The work also has wider implications for other studies, as paleoclimatologist Konrad Hughen of the Woods Hole Oceanographic Institution explained: “Our approach offers the huge potential to unravel the role of climate in critical events of the recent fossil record as it can be applied to any radiocarbon date from any deposit.”

http://www.eurekalert.org/pub_releases/2007-09/uol-neo091107.php
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scientists point at climate changes as the cause of the Neanderthal extinction by coldrum on Tuesday, 22 May 2007
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scientists point at climate changes as the cause of the Neanderthal extinction

Climate – and not modern humans – was the cause of the Neanderthal extinction in the Iberian Peninsula. Such is the conclusion of the University of Granada research group RNM 179 - Mineralogy and Geochemistry of sedimentary and metamorphic environments, headed by professor Miguel Ortega Huertas and whose members Francisco José Jiménez Espejo, Francisca Martínez Ruiz and David Gallego Torres work jointly at the department of Mineralogy and Petrology of the University of Granada (Universidad de Granada [http://www.ugr.es]) and the Andalusian Regional Institute of Earth Sciences (CSIC-UGR).

Together with other scientists from the Gibraltar Museum, Stanford University and the Japan Marine Science & Technology Center (JAMSTEC), the Spanish scientists published in the scientific journal Quaternary Science Reviews an innovative work representing a considerable step forward in the knowledge of human ancestral history.
The results of this multidisciplinary research are an important contribution to the understanding of the Neanderthal extinction and the colonisation of the European continent by Homo Sapiens.

During the last Ice Age, the Iberian Peninsula was a refuge for Neanderthals, who had survived in local pockets during previous Ice Ages, bouncing back to Europe when weather conditions improved.

Climate reconstructions

The study is based upon climate reconstructions elaborated from marine records and using the experience of Spanish and international research groups on Western Mediterranean paleoceanography. The conclusions point out that Neanderthal populations did suffer fluctuations related to climate changes before the first Homo Sapiens arrived in the Iberian Peninsula. Cold, arid and highly variable climate was the least favourable weather for Neanderthals and 24,000 years ago they had to face the worst weather conditions in the last 250,000 years.

The most important about these data is that they differ from the current scientific paradigm which makes Homo Sapiens responsible for the Neanderthal extinction. This work is a contribution to a new scientific current – leaded by Dr. Clive Finlayson, from the Gibraltar Museum – according to which Neanderthal isolation and, possibly, extinction were due to environmental factors.

These studies on climate variability are part of the work of the group RNM 179, funded by the excellence project RNM 0432 of the Andalusian Regional Government’s Department for Innovation, Science and Business and by the MARCAL project of the Spanish Ministry of Education and Science, both linked to the Andalusian Environment Centre (CEAMA - Centro Andaluz de Medio Ambiente).

http://www.alphagalileo.org/index.cfm?fuseaction=readrelease&releaseid=520114&ez_search=1
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