Freeze 'Condemned Neanderthals'

Small pockets of Neanderthals clung on in the south (Image: Gibraltar Museum)

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.

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.

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.

Neanderthals held on at sites like Carihuela (Image: S Fernandez Jimenez/J Carrion)

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.

"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.

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.

Pollen records the environment in which Neanderthals lived (Image: S Fernandez Jimenez/J Carrion)

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.

Date: February 18, 2007

Birth Rate, Competition Are Major Players In Hominid Extinctions

Science Daily — Modern human mothers are probably happy that they typically have one, maybe two babies at a time, but for early hominids, low birth numbers combined with competition often spelled extinction. "The lineages of primates have some traits that make it hard for them to respond to rapid perturbations in the environment," says Dr. Nina G. Jablonski, professor of anthropology and department head at Penn State. "Through time we see a lot of lineages become extinct when environments where the species are found become highly seasonal or unpredictable."

Primates evolved in the Paleocene and Eocene when worldwide climate was less seasonal. The beneficial environment allowed primates to evolve as relatively brainy animals that reproduce slowly. However, when climate changed so that tropical forests shrunk and the environment became patchy, many species including primate species became extinct.

"While past primate populations moved with the forest, early hominid cultures 2.5 million years ago show signs of the ability to live in marginal areas and live on more dynamic, seasonal landscapes," Jablonski told attendees today (Feb. 16) at the annual meeting of the American Association for the Advancement of Science in San Francisco.

Through time, the human lineage evolved to fill a wide variety of ecological niches, but those species that filled narrow environments, were less able to withstand the effects of climate change. Paranthropus boisei, a Pleistocene hominid, thrived around 2.5 million years ago, but disappears from the fossil record a million years ago. Paranthropus boisei became extinct when it was unable to compete with other mammals.

A specialized feeder, Paranthropus boisei dined on hard objects like seeds, tubers and bones. While it had a variety of food sources, they all required the crunching, grinding force of its teeth. Unfortunately, bush pigs and hyenas had great grinding and crushing teeth, too, and went after the same food. Paranthropus could not compete because it produced one offspring a year at most, while the others had large litters and could increase their populations at a much faster rate. Paranthropus simply could not compete reproductively and could not alter its choice of food.

"We find that the early members of the genus Homo who succeeded were super ecological opportunists," says Jablonski. "They would eat vegetation and scavenge, kill small animals and forage."

Cultural adaptations helped these opportunists to take advantage of whatever food was available. But culture did not seem to help the Neandertal. Tremendously successful from about 200 to 50 thousand years ago, they suffered a gradual decrease and extinction from about 30 to 26 thousand years ago.

"Neandertal was extremely adept culturally," says Jablonski. "They had big brains, a wide variety of tools and were extremely successful as active, aggressive hunters of large game. We see evidence of hunting, kill sites, butchery and even herding off cliffs. We find thrusting spears and butchering knives." The Neandertal encountered increasing environmental seasonality with longer cold seasons and shorter periods of warm weather. Leading up to and during the last glacial maximum about 18,000 years ago, the grassy plains disappeared, taking with them the animals that relied on large expanses of grass for grazing. These animals were the prime food source for Neandertal.

At the same time, modern Homo sapiens experienced the same reduction in large animal game, but switched to also fishing, snaring small mammals like rabbits and capturing turtles and birds.

"Rather than being a specialized large mammal predator, modern humans would eat anything they could get their hands on. They eked out a living even if it meant eating grasshoppers or whatever," says Jablonski. "Even with this, modern humans barely hung on from 12 to 16,000 years ago.

"Why did Neandertal not adapt culturally?" she asks. "Why did they not start eating bunnies? They did begin fishing."

Jablonski believes that competition from modern humans was already too strong. The environment was marginal and modern humans were already foraging and small-animal collecting.

"I think they were out-competed at the very end," says Jablonski. "Modern humans simply did it better, more nimbly."

She adds that modern humans may have had storage capabilities that Neandertal did not. There is evidence that modern humans did have the capacity to store food and water in the late Pleistocene. No evidence exists that Neandertal could store either.

Both Neandertal and modern humans suffered from the primate curses of single births widely spaced. For Neandertal, cultural adaptation was not sufficient to overcome and compete with modern humans, just as Paranthropus boisei could not compete with the likes of bush pigs and hyenas. " Can we, today, control our cultural behavior to ensure our environmental success," says Jablonski. "Can we control growth and population density, or come up with new technology to overcome the problems we will face from the global climate change we have created?

"We clearly have the cultural ability to do either," says the Penn State researcher. "But both require forethought and planning to face the demographic and climate change. A degree of honesty, our species is not known for."

Note: This story has been adapted from a news release issued by Penn State.

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