Mankind has gotten a really bad rep lately as environmentalists blame us for everything from blizzards to droughts to rising sea levels and the infinitesimal warming in the last 100 years. So it’s refreshing to read today that when woolly mammoths disappeared 11,000 years ago, we had little, if anything, to do with it. That’s according to a new study detailing how researchers set out to discover why these giant animals went extinct after the last glacial period.
Most theories put forth suggested their demise came from the over-eager predation and habitat intrusion of man. But these new findings showed that abrupt global warming helped kill off the woolly mammoth and that we had a small, secondary role. The study’s lead author, professor Alan Cooper, who is the director of the Australian Centre for Ancient DNA at the University of Adelaide, said “This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns. Even without the presence of humans we saw mass extinctions.”
That’s because short, rapid bursts of global warming dramatically altered rainfall amounts, which in turn resulted in a dearth of vegetation that these ice age animals relied on for sustenance. Humans also played a role, albeit smaller, by hunting these large animals (megafauna) across the Northern Hemisphere. Couple the lack of rainfall and food in a warming climate, and the death knell was rung for woolly mammoths, as well as other ice age creatures.
Scientists have long debated whether the disappearances of large ice-age species were due to “environmental influences or human activity.” By analyzing the ancient DNA extracted from the fossilized remains of the extinct ice-age animals, they were able to compare it to the “climate data stretching back some 56,000 years.”
But to get this climate timeline, Cooper et al used ice core samples obtained from Greenland. They recorded climate changes during the Late Pleistocene age, which was largely dominated by retreating glaciation. They then compared “ancient DNA and radiocarbon data from 31 detailed time series of regional megafaunal extinctions/replacements … with standard and new combined records of Northern Hemisphere climate.”
The scientists noticed that bursts of warming coincided with major extinction events, long before the appearance of man. In fact, the human species (other than modern man) died out during the Pleistocene age, a period “marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places.” Many megafauna also became extinct over this time period, a trend that continued into the Holocene age, the one we’re currently experiencing.
The DNA analysis provided information about “extinction events by allowing researchers to look for periods when populations of the animals became restricted or contracted, causing a loss in genetic diversity.” It showed that when the climate rapidly warmed, “ice age giants like the mammoths and giant sloths didn’t fare as well as expected.”
Scientists also compared the genomes of two woolly mammoths with those of Asian elephants, their nearest biological cousin. They found differences in over 1,600 genes, which changed the mammoth’s “skin, hair, fat storage, metabolism and temperature sensation and allowed them to survive the freezing temperatures during the last ice age.”
One of the genes, known as TRPV3, is thought to be responsible for a mammoth’s sensitivity to cold. But once the planet started warming up as it left the last glacial period, the mammoths were “ill equipped to cope.” After repeated successions of warm periods, more of the ice age animals began to die off, and modern-day man started flourishing in the once-inhospitable Northern Hemisphere. It also takes an exceptionally long time of sustained multi-decadal warmth to melt the glaciation that occurred during the Pleistocene age. (It took almost five months to melt a man-made 60-foot-high parking lot-sized glacier to melt in Boston this summer.)
What this study also shows is that the Earth has been going through these short and long stretches of warming and cooling for millions of years, a natural phenomenon that will continue for thousands of millennia to come. Maybe they can use the megafauna DNA to create a Pleistocene Playground, à la Jurassic Park, though probably not a good idea.
The study was published by Science and is available online.