매머드 멸종 진짜 이유는 인간의 사냥 탓

코끼리와 비슷하게 생긴 거대한 포유류인 매머드는 국내에서도 인기를 끈 미국 애니메이션 시리즈 ‘아이스에이지’의 단골 캐릭터로 등장할 만큼 전 세계적으로 인기가 높다. 이 멋진 동물은 20만년 전부터 남아메리카와 호주 등 아주 일부 지역을 빼고는 지구 전역에 광범위하게 걸쳐 살았다. 하지만 대부분 1만년 전에 갑자기 지구에서 종적을 감췄다. 아주 극소수 살아남은 무리 500~1000마리만이 약 3600년 전까지 북극해의 랭글섬에 살아남았던 것으로 추정된다. 

매머드가 갑자기 지구에서 종적을 감춘 이유에 대한 이론이나 가설은 많다. 1만2900~2만여년 전 갑작스레 빙하기가 찾아와 먹이를 찾지 못해 멸종됐다는 이론이 있는가 하면, 빙하기가 끝나고 매머드가 살만한 땅이 사라지면서 자취를 감췄다는 설도 있다. 일부 과학자는 혜성 충돌, 화산 폭발을 원인으로 지목하기도 하고, 최근에는 인류의 사냥이 매머드를 멸종시켰다는 견해가 설득력을 얻고 있다. 

최근 영국의 엑서터대와 케임브리지대 연구진은 매머드와 같은 전설 속 동물들이 멸종한 건 기후 변화나 다른 갑작스러운 환경변화가 아닌 인류 때문이라는 연구 결과를 발표했다. 과학자들은 지금은 화석으로나 만나 볼 수 있는 매머드와 검치호랑이, 거대나무늘보, 털코뿔소 등은 선사시대의 거대 포유류가 약 8만년 전부터 서서히 사라지다가 1만년 전을 전후해 완전히 사라졌다고 보고 있다. 하지만 이들 동물의 멸종 이유에 대한 논란은 50년 넘게 이어지고 있다. 

연구진은 첨단 통계 분석 방법을 이용해 선사시대 인류가 세계 각지로 흩어져 나간 시기와 각각의 종들이 특정 지역에서 사라진 시기를 연결지어 수천 가지 시나리오를 분석했다. 이어 인간의 정착 시기와 멸종 시기가 사실상 일치한다는 점을 확인했다. 

루이스 바틀렛 엑서터대 생태보존센터 연구원은 “최근 일련의 연구 결과 초기 정착민들이 포유동물을 잡아먹고 불을 이용하거나 서식지를 몰아내면서 멸종을 부추긴 것으로 보인다”며 “초기 인류가 자연과 조화를 이루며 살았다는 그간의 믿음이 틀렸다는 사실이 드러났다”고 말했다. 인류가 자신의 생활권을 확대하면서 매머드가 사냥감이 되거나 서식지에서 내몰렸고 결국 무리를 계속해서 유지할 만큼 개체 수를 확보하지 못하면서 위태로워졌다는 분석이다. 고생물학자들은 인간의 공격에 생존의 위기를 맞은 매머드들이 때마침 찾아온 기후 변화에 결정타를 맞았을 것으로 보고 있다. 새로운 환경에 적응하지 못한 동물과 복잡한 요인이 맞물려 멸종을 가져왔다고 보고 있다. 이번 연구는 선사시대 인간의 활동이 지금은 사라진 전설 속 동물들의 멸종과 직접 관련이 있다는 사실을 밝힌 데 의의가 있다는 평가다. 

안드레아 매니커 케임브리지대 교수는 “다른 지역에선 인간과 기후변화로 거대 포유류가 급속히 멸종했지만 아시아만큼은 달랐다”며 추가 연구의 필요성을 제기했다. 과학자들은 아시아에 서식하던 거대 포유류들이 ‘외부의 충격’에 견딜 수 있었던 이유를 찾고 있다. 이 연구는 국제학술지 에코그래피 최신호에 소개됐다. 

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Humans DID kill off the woolly mammoth

: Spread of mankind coincides with extinction of ice age beasts, claims study

• Scientists claim to have definitively solved what caused the extinction of woolly mammoths, giant armadillos and other ice age beasts
• They compared extinction events in different areas with the spread of man
• They say early humans moved into areas and giant mammals then died out
• Climate change added pressure but in Asia another factor was responsible

By Richard Gray for MailOnline

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It is one of the most enduring mysteries in the Earth's history, but scientists believe they can finally point the finger at humans for wiping out ice age giants like the woolly mammoth.

The extinction of giant beasts like mammoths, woolly rhinos and giant armadillos around 10,000 years ago has been debated by scientists for more than a half a century.

Researchers have previously blamed the mass extinction on climate change, meteor impacts, volcanoes, habitat loss and even disease.

Now a team of scientists at the University of Exeter and the University of Cambridge have used statistical analysis to unravel the mystery and put humans back in the frame.

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The extinction of ice age giants like the woolly mammoth has been a controversial topic for more than half a century but using sophisticated computer analysis of data from fossils, climate data and archaeological evidence, a new study has found humans were the main cause of their demise, as illustrated above

They found that whenever prehistoric humans spread to on continents and islands, the megafauna quickly died out.

This, they say, is the 'nail in the coffin' that puts humans firmly in the frame for the genocide of millions of some of the largest land mammals to have walked the Earth.

Lewis Bartlett, an ecologist at the University of Exeter who has been studying megafauna extinctions and led the work, said: 'As far as we are concerned, this research is the nail in the coffin of this 50-year debate - humans were the dominant cause of the extinction of megafauna.

'What we don't know is what it was about these early settlers that caused this demise.

'Were they killing them for food, was it early use of fire or were they driven out of their habitats?

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Scientists have debated what killed off woolly mammoths (above) and other ice age giants for decades, with illness and human hunters being among the favourite theories. Now a team of researchers has conducted analysis which they say shows these extinctions coincided with the arrival of humans on continents 

'Our analysis doesn't differentiate, but we can say that it was caused by human activity more than by climate change.

'It debunks the myth of early humans living in harmony with nature.'

Despite the emphatic claims, however, the debate is likely to continue as new research continues to uncover evidence for competing theories.

Last month, DNA analysis of mammoth and other ancient species published in the journal Science found climate change was chiefly to blame for the loss of large ice age mammals.

MYSTERY OF WHAT KILLED OFF THE MAMMOTHS

There are several leading theories for what killed off the ice age giants like the woolly mammoths.

Woolly mammoths are thought to have roamed the Earth from about 200,000 years ago before eventually dying out 10,000 years ago.

At this time the planet was undergoing a major change in climate that is thought to have led to the shrinkage of their habitat.

Unable to find the food they needed their populations became smaller and increasingly isolated.

A study in 2008 estimated that changes in climate as a result of the end of the last glacial period saw their habitat shrink from 3 million square miles to 310,000 square miles.

Some researchers have suggested that the spread of forests, which overtook the extensive areas of frozen grassland and tundra where mammoths thrived, led to their extinction.

The changes in climate also opened up large parts of the northern hemisphere to humans, allowing groups to spread more widely around North America, Asia and Europe.

Many blame overhunting by humans for finally finishing off the dwindling populations of megafauna like mammoths.

More recently some scientists have adopted theories that sudden changes in climate, known as the Younger Dyas period, left many large animal species unable to cope.

It is thought this period of cooling may have been caused by the collapse of the North American ice sheets into the Atlantic Ocean, leading to the seas cooling dramatically.

Others have suggested this was triggered by a large explosion from an asteroid or comet impact that spread debris around the globe.

Some of the largest mammals to have roamed the Earth, such as woolly mammoths and woolly rhino, shown in the illustration above, died out in a mass extinction that ended around 10,000 years ago with the end of the last ice age. The spread of humans around the globe seems to be the main cause according to the new research

It said the humans had merely delivered the final blow to species pushed to the brink by periods of rapid warming.

Other researchers have put forward evidence that an asteroid or comet impact threw debris around the globe that triggered rapid periods of cooling.

HOW MAMMOTHS BRAVED THE COLD

Genetic research on woolly mammoths has helped to reveal how the ice age giants adapted to survive in the cold expanses of northern Asia and Europe.

Scientists compared the genomes of two woolly mammoths with those of Asian elephants - their closest living relatives - in an attempt to understand the differences between them.

The research found that woolly mammoths and Asian elephants have nearly 1.4 million DNA letters difference between their genomes.

These difference alter more than 1,600 genes, bringing about changes in skin and hair development, fat storage, metabolism and temperature sensation.

One mammoth gene, known as TRPV3, was involved in sensitivity to the cold.

It is thought these adaptations allowed the mammoth to survive in the freezing temperatures during the last ice age, but it is possible they left them ill equipped to cope as the climate warmed.

However in the latest work published in the journal Ecography, Mr Bartlett and his colleagues used computer modelling to analyse scenarios which mapped the time periods in which each species is known to have become extinct.

This was compared with the times when humans are known to have arrived in different continents and islands.

This was also compared against climate reconstructions for the last 90,000 years.

They found human spread seemed to coincide with species extinctions in all but a handful of cases.

In particular, they believe mankind was the main agent causing the demise of the animals with climate change perhaps exacerbating the number of extinctions.

However, in certain regions of the world, particularly in Asia, they found patterns which did not match either of these two drivers.

This suggests something else was to blame for causing the animals here dying out.

In reality, many palaeontologists believe it may have been a complex combination of factors, combined with the animals inability to adapt, that led to their eventual extinction.

Dr Andrea Manica, an evolutionary ecologist at Cambridge University who was the lead supervisor behind the research, said: 'Whilst our models explain very well the timing and extent of extinctions for most of the world, mainland Asia remains a mystery.

'According to the fossil record, that region suffered very low rates of extinctions. Understanding why megafauna in mainland Asia is so resilient is the next big question.'

http://www.dailymail.co.uk/sciencetech/article-3196817/It-humans-killed-mammoths-Spread-mankind-coincides-extinction-ice-age-beasts-claims-study.html