Thursday, February 5, 2015

Neanderthal Driven Extinct by Homo sapiens or Climate Change?

Kate Wong is an Editor at Scientific American and over the past half a decade has published a series of in depth articles on her favorite topic, the Neandertal. You should check out the latest in this series in the February Scientific American. This species, Neandertal, our closest relatives, ruled Europe and western Asia for 200,000-210,000 years. About 44,000 years ago modern humans, Homo sapiens, who evolved in Africa spread to Europe and western Asia and beyond. Improved dating methods applied by scientists from Oxford University to dozens of Neanderthal and Homo sapiens sites indicate that over a period of about 2,600-5,400 years both species coexisted in Europe until the Neandertal disappeared from the archeological record around 39,000 years ago.

Scientists have long debated what led to the disappearance of the Neandertal. Before improvements in dating methods showed that rather than disappearing immediately after Homo sapiens invaded Europe, it was believed that Homo sapiens simply replaced the Neanderthal. They were either conquered or out competed. For over a century Neandertals were considered an inferior species to Homo sapiens. However, in this century there has been a major reassessment of the Neandertals. New discoveries about Neandertals in archaeology have forced re-evaluations of their anatomy, the size of their brains, their cognitive ability, and revelations about their genetic makeup.

In 1997 when the first DNA studies using DNA obtained from three Neandertal bones from the Vindija cave in Croatia were done they sequenced Neandertal mitochondrial DNA and did not find any commonality with modern man. Mitochondria have their own DNA, which is distinct from the much longer DNA sequence that resides in the cell’s nucleus. The findings in 1997 were that Neanderthals had not made any contributions to modern Homo sapiens mitochondrial DNA.

However in 2010, the same team successfully sequenced the nuclear DNA and looked at patterns of nuclear genome variation in present-day humans. They identified 12 genome regions where non-Africans exhibited variants that were not seen in Africans and that were possibly derived from the Neandertals, who lived not in Africa but Eurasia (Europe and western Asia). The scientists have since concluded that between 1.5%- 2.1% of the DNA of people today who live outside Africa came from Neandertals, the result of interbreeding.

These results of the DNA sequencing and better dating disprove the strict Out of Africa replacement model of modern human origins. This was the theory that was in vogue when I studied Anthropology. Dr. Christopher B. Stringer of the Natural History Museum in London has revised that theory saying “the Neandertal genome strongly suggests those genes were not lost, and that many of us outside of Africa have some Neandertal inheritance.”

The latest research has found that the Neandertal fashioned and used bone tools for working hides 53,000-41,000 years ago. From a Neanderthal site 90,000 years old is evidence of string making possibly for nets, traps and bags. Traces of worked wood indicating tool making have been found. Work by the Max Planck Institute for Evolutionary Anthropology in Germany has found evidence throughout Europe and western Asia that Neandertals were omnivores that consumed cooked wheat, tubers and barley and were making and using stone tools. Recent discoveries have found that Neandertals were tool makers, omnivores and engaged in symbolic thought (cave art) before the arrival of Homo sapiens. These findings have made the decline and extinction of the Neanderthal more puzzling.

The latest extinction theories focus on climate change and subtle differences in behavior and biology. That is not surprising since all current scientific theories focus on climate change. The theory is that Homo sapiens evolved a unique combination of physical and behavioral characteristics that Neandertal did not possess at least to the same degree. The complex brains of Homo sapiens enabled them to interact with each other and with their surroundings in new and different ways. As the environment became more unpredictable, bigger brains helped Homo sapiens survive. The Neanderthal ruled Europe and Western Asia (Eurasia) for over two hundred thousand years through periods of changing climate, but died out because they did not adapt to climate change.

The Neandertal were a more spread out and less connected population than the more densely populated Africa home of the Homo sapiens. The vast spans of ice isolated the groups from one another. Once the glaciers melted and the European and western Asia continents were more hospitable, Homo sapiens swarmed into Europe and western Asia and lead to the Neandertal demise by dramatic population increases, taking over the Neandertal hunting and gathering grounds and swamping their gene pool.

Population pressure has driven Homo sapiens. In just the past 12,000 years Homo sapiens have transitioned from hunting and gathering to producing food and changing our surroundings. Food and population pressure led to farming and herding animals. As Homo sapiens invested more time in producing food, they ceased to be nomad tribes. Villages became towns, and towns became cities. We learned to build, to move water, build pumps and engines and burn fossil fuels to put ever more Homo sapiens on earth.

With more food available, the human population continued to increase dramatically. Homo sapiens spread to every continent and geometrically expanded their numbers; there are over 7 billion of our species on earth today. Homo sapiens have altered the world in ways that benefit them greatly. The transformation has unintended consequences for other for other species as well as for our own. Our great strength may also prove to be a challenge to our survival.

In 2013 when the Intergovernmental Panel on Climate Change (IPCC) released the Fifth Assessment Report on climate change they reported that the IPCC expects global surface temperatures for the end of the 21st century to increase 2.7°F to 3.6°F relative to 1850 to 1900 time period. “Heat waves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions,” said Co-Chair Thomas Stocker in the press release. Dr. Stocker concluded his comments by reminding us that as a result of our past, present and expected future emissions of CO2, climate change is inevitable, and will persist for many centuries even if emissions of CO2 were to stop today. So we get to see if and how Homo sapiens survive climate change.

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