A 38,000-YEAR-OLD WHODUNIT: WHAT REALLY HAPPENED TO OUR NEANDERTHAL COUSINS?

Neanderthals--those brawny, heavy-browed but big-brained cousins of ours--thrived across Europe and Asia for some 300,000 years. Then, in the course of just a few thousand years, they vanished, leaving only some bones, beads, stone tools, an enigmatic burial or two, and a scattering of their genes in our species, Homo sapiens. 

Since the discovery of the first H. neanderthalesis skeleton in 1856, scientists have speculated and argued about what caused their extinction. There have been lots of ideas, including climate change, disease, lack of genetic variability, interbreeding with, competition with, or outright extermination by H. sapiens.

Reconstruction of a Neanderthal woman

Credit: Bacon Cph

New research using a dynamic supercomputer model incorporating climate shifts, geography, food resources, utilization of resources and interbreeding solves they mystery. It was us, modern humans at first filtering in from Africa and then expanding our range across Asia and Europe, who did them in.

According to the study, the extinction of the Neanderthals didn't require warfare and slaughter at our ancestor's hands; all that was needed was a competitive edge. Models in which those early modern humans could exploit local resources more efficiently and so support a larger population inevitably showed the Neanderthal range and population shrinking and, within a few thousand years, vanishing. The researchers call this "competitive exclusion."

"It is not a coincidence that Neanderthals vanished just at the time when Homo sapiens started to spread into Europe," says Axel Timmerman, a climate physicist at Pusan National University, in South Korea. "The new computer model simulations show clearly that this event was the first major extinction caused by our own species."

The model that Timmerman developed folded together a huge amount of information. It modeled the climate across northern Africa, Asia and Europe over the 100,000 years that preceded the Neanderthal extinction around 38,000 years ago, regional productivity of potential food sources, population densities of Neanderthals and modern humans across time and space, and interbreeding between the two species.

Running the model on the ALEPH supercomputer at Pusan National University, Timmerman was able to see the shifting populations of Neanderthals and H. sapiens across Asia and Europe over the millenia under different conditions of climate, interbreeding and competition.

One factor that emerged clearly was that climate change alone was not the cause of the Neanderthal's extinction. This bears out the observation that they had survived hundreds of thousands of years of climate change, including periods of severe glaciation. "Neanderthals lived in Eurasia for the last 300,000 years and adapted to abrupt climate shifts that were even more dramatic than those than occurred during the time of Neanderthal disappearance," says Timmerman. It was only after the arrival of modern humans that Neanderthal populations began an irreversible decline.

Timmerman concludes that the anatomically modern humans who found their way into Eurasia around 50,000 years ago simply out-competed the Neanderthals. His model doesn't specify exactly what differences drove that competitive edge. Even if the modern humans simply were able to harvest more food from the environment, or were more resistant to diseases, or managed to raise more children to adulthood, that could have been enough to allow them to displace and eventually replace the Neanderthals.

In other words, one way or another, the culprit was us.

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You can find the full, open-source research paper at this URL. It's worth scrolling down to the appendix, where you can watch movies depicting the influx and growth of the H. sapiens population and the decline and disappearance of the Neanderthals over time and space. Fascinating.

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REA

Goodbye, Gorillas

The already threatened gorillas of Africa are likely to be wiped out by even the two degree Celsius temperature rise set in Copenhagen today as one of the goals of the world community.

Dr. Amanda Kortjens, of Bournemouth University in the UK, and her colleagues based their conclusions on studies of the need for gorillas and other leaf-eating primates to have enough time to forage, socialize, and rest. Gorillas are forced to rest when temperatures get too high, which reduces the time available for them to find food and maintain social ties.

Coupled with the intense threats gorillas already face from habitat loss and hunting as "bush meat", even this seemingly modest rise in temperature will put them at risk of extinction.

This piece of research, which will appear in Animal Behaviour, December, 2009, serves as yet one more example of how seemingly innocuous or supposedly acceptable levels of global warming can have unacceptable, even non-survivable, effects on certain populations or in certain regions.

Robert Adler

for the institute

How much atmospheric CO2 can we live with?

That’s the question James Hansen, director of the NASA-Goddard Institute for Space Studies, addressed on October 7 at the Joint Annual Meeting of the Geological Society of America, in Houston, Texas.

His short answer is less than 350 parts per million—the level Hansen believes will preserve Earth’s ice sheets, mountain glaciers, and head off a devastating sea-level rise.

The fact that we have now surged past 387 parts per million of CO2, with no effective control in sight, is alarming. 

A state of emergency

“I believe we’ve reached a state of emergency,” Hansen said, “although it’s not easy to see. But if you look at the science, it becomes clearer and clearer.”

It’s enough of an emergency to force him to rethink nuclear power, an issue on which he’s previously been “an agnostic.” Renewable energy alone in sufficient quantities, he said, would be too costly.

 

Hansen walked the audience through the science—ice cores that reveal CO2 levels over the past 800,000 years, microscopic shells from under the sea floor that track ocean bottom temperature and salinity for the past 35,000,000 years, reconstructions of past glaciations and sea levels, the current rates at which the Earth is warming and its ice sheets disintegrating, and computer models of the climate system.

The bottom line is that the amount of CO2 in the atmosphere drives Earth’s climate, and that we are driving CO2 off the charts.

“All we have to do is graph the greenhouse gas forcing over the past several hundred thousand years,” says Hansen. “When we choose the right scale, it’s a hand and glove fit. Humans are now completely in charge of the composition of the atmosphere. CO2 and methane are far outside the range they’ve been in for millions of years.”

We’re in charge but out of control

Did you catch that—“Humans are now completely in charge of the composition of the atmosphere.” In charge, but out of control, like airplane without a pilot.

We’re not even close to heading in the right direction. Even countries that signed on to the Kyoto Accord have increased their carbon emissions. There’s more CO2 in the atmosphere than at any time in the last 650,000 years, and the rate at which it’s increasing is itself increasing.

“The actual actions of countries worldwide are inconsistent with stopping the CO2 rise,” Hansen said. “Energy departments around the world are assuming we can burn all the remaining fossil fuel. That will double or triple atmospheric CO2.”

What that means, he said, is that unless global carbon emissions are cut drastically, and soon, we’re headed for “. . . a completely different planet than the one that’s existed in the past. Obviously, it would be an ice-free planet, warmer than it’s been in any of the recent interglacials.” 

Among other impacts Hansen foresees is the disappearance of glaciers in the Himalayas, Rockies, and Andes within the next few decades, threatening the water and food supplies of hundreds of millions of people. 

Hmm. Where would they go, and what kinds of upheavals would that kind of mass migration cause?

Irreversible tipping points

Hansen also warned about climatic and environmental tipping points, “where the dynamics of the system take over and you don’t need any more forcing and there’s the potential to lose control.”

One example is the disintegration of the ice sheets. “It takes thousands of years to build up an ice sheet from snowfall,” he said. “If we cause the West Antarctic ice sheet to disintegrate, that’s essentially irreversible.”

“I think that the metric for what is dangerous should be headed by these irreversible effects, such as the extermination of species,” he said. “We know that when there have been warmings of several degrees in the past, more than half of the species on Earth at that time went extinct.”

Remarkably, Hansen remains optimistic about our ability to push CO2 levels back below 350 parts per million and turn this looming catastrophe around. The keys are technology and public policy.

One necessary ingredient, he says, is to cut back immediately on the burning of coal as well as other fossil fuels. “We could say that we’ll only use coal at power plants where we will capture and sequester it,” he said.

Hansen also wants to see carbon emissions taxed. “The public has to understand that we have to put a price, a tax, on carbon emissions,” he said. “That has to be given back, so the person who reduces his carbon emissions more than average will make money.”

Hansen is now re-examining nuclear power. In principle, he says, fourth generation reactors can burn nuclear fuel far more efficiently than in the past, while generating much less--and less dangerous--waste.

“I think we should be doing the research on nuclear power and having a trial of fourth generation technology, because that may very well be necessary,” he said.

Crimes against humanity and nature

From Hansen’s point of view, business-as-usual versus re-stabilizing the climate is an intergenerational conflict with enormous moral and legal implications.

“It’s an inequity and an injustice for the young and the unborn,” he said. I think it raises ethical and legal questions about liability. There has been intentional misinformation of the public, which makes the companies that engage in that and fund the contrarians to misinform the public ethically and I think legally liable for what I call crimes against humanity and nature.”

Hansen does not believe that the free market alone can or will solve this problem. “The profit motive seems to be so strong that I don’t think we can rely on their conscience to change things,” he said. “We have to rely on public policy.”

Hansen has consistently and courageously advocated on behalf of a stable climate and a viable future for our children. We need to make sure our leaders know he's not alone, and that this may be our last chance to act.