Ice Age, mammoth

Extinction Era

What killed the woolly mammoth? Scientists debunk one extinction theory

Humans may be off the hook.

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Thousands of years ago, massive woolly mammoths roamed the Mammoth Steppe — a chilly, but flourishing Arctic ecosystem that was once the largest biome on Earth. These megafauna trampled high grasses and fed on ample vegetation.

Woolly mammoths thrived there — until they disappeared. According to some scientists, the appearance of humans in the Arctic coincided with the extinction of the woolly mammoth.

Now scientists have a new hypothesis — one that lets humans off the hook for the animal’s demise. It also suggests a new timeline for woolly mammoth extinction.

The findings were published Wednesday in the journal Nature.

The argument over what caused Arctic megafauna extinction overall has “been debated for more than a hundred years,” lead author Yucheng Wang, a research associate at Cambridge University, tells Inverse. Proposed causes have ranged from human overkill to climate change.

Wang’s research points to the latter, suggesting woolly mammoths coexisted with humans for an estimated 2,000 years until the animals were eventually undermined by a changing climate.

A woolly mammoth skeleton on display in England. Peter Macdiarmid/Getty Images

How the discovery was made — Scientists have relied on DNA from fossils to understand Arctic megafauna, but with a limited supply of fossil specimens, it’s hard to make accurate claims about when the woolly mammoths disappeared or whether humans were the exact cause of their demise.

This is why Wang and colleagues turned to a relatively newer method: To solve the question of what happened to mammoths, they examined environmental DNA or “eDNA” from plants and animals found within what was once the Mammoth Steppe.

Wang describes eDNA as the DNA molecules preserved in environmental samples like soil, water, air, and other biological samples. For example, animals shed eDNA through urine, dung, bone fragments, hair, and skin cells.

A 1902 excavation of a frozen woolly mammoth in Russia. Sovfoto/Universal Images Group via Getty Images

These DNA molecules attach to soil particles once released from plants and animals. Over time, the DNA gets compacted into different soil layers — different layers represent different time periods, allowing researchers to understand the age of these ancient animals.

The study team extracted and sequenced eDNA within soil layers, and compared this data against DNA extracted from modern Arctic plants. They gathered more than 500 plant and animal eDNA samples from the past 50,000 years.

While the researchers didn’t invent the technology, Wang says his team “developed a series of new methods that allowed an improved application of eDNA,” allowing for more refined genetic sequencing and better identification of species.

The technology revealed changing Arctic vegetation and climate patterns — essential clues for understanding how the woolly mammoth lived and died.

The study revealed four key findings:

1. The woolly mammoth survived until 3,900 years ago in Siberia.

Researchers previously believed woolly mammoths went extinct around 10,000 years ago.

2. The mammoth likely survived for longer than we expected because of plant resilience.

The study suggests the unique vegetation of the Mammoth Steppe in northern Centra Siberia also existed for thousands of years longer than realized, which helped keep the mammoth alive.

3. Mammoths “encountered and co-existed with humans” for some 2,000 years.

As a result, there’s no way “human overkill” caused the extinction of mammoths within centuries after first human contact, as some scientists previously theorized.

4. Instead, the model suggests climate change and shifting vegetation patterns led to the deterioration of the Mammoth Steppe’s ecosystem.

These were “the main drivers” of mammoth extinction.

The study suggests warming temperatures after the Last Glacial Maximum — when ice sheets were their thickest — caused ice sheets to melt, which created more wetland plants on the Mammoth Steppe. It was harder for mammoths to access the natural resources of the wetter, softer ground compared to the firmer tundra of the Mammoth Steppe.

Wang says these findings clearly shift the blame from humans. “We found the distribution of humans over time was almost entirely unrelated to the presence of megafauna,” he says.

A snapshot of the modern-day Arctic. A changing Arctic landscape and shifting plant patterns likely led to the demise of the woolly mammoth. Inger Greve Alsos

Why it matters — The new study updates our timeline of when the mammoth disappeared and what may have led to its extinction.

The scientists also found the Mammoth Steppe contained a more balanced pattern of vegetation — as opposed to being dominated by grass — suggesting ancient herbivores like woolly mammoths and woolly rhinos had a more diverse diet than assumed.

These discoveries were possible because of eDNA and speak to the power of using emerging technology to solve ancient mysteries.

What’s next — The scientists hope to sequence and analyze even more Arctic eDNA. Specifically, Wang has two future goals:

  1. “Analysing the DNA of ancient microbes in this dataset” to create a “more comprehensive picture” of the Arctic’s natural history — big and small.
  2. Researching the “functional genes” of ancient animals and plants to help scientists “understand how genetically climate change will affect ecosystems.”

Meanwhile, other scientists have proposed something a bit more audacious: Using gene-editing technology to bring the wooly mammoth back from extinction. Other scientists are even attempting to create a “Pleistocene Park” in Siberia to restore the ancient Arctic ecosystem of the Mammoth Steppe. (Today the Ukok Plateau in southwestern Siberia is considered one of the last remnants of the Mammoth Steepe.)

If scientists are successful in bringing the woolly mammoth back, they could possibly return to an environment similar to the home of their predecessors. The question is: Should scientists even try?

Abstract: During the last glacial-interglacial cycle, Arctic biotas experienced substantial climatic changes, yet the nature, extent and rate of their responses are not fully understood1–8. Here we report a large-scale environmental DNA metagenomic study of ancient plant and mammal communities, analysing 535 permafrost and lake sediment samples from across the Arctic spanning the past 50,000 years. Furthermore, we present 1,541 contemporary plant genome assemblies that were generated as reference sequences. Our study provides several insights into the long-term dynamics of the Arctic biota at the circumpolar and regional scales. Our key findings include: (1) a relatively homogeneous steppe–tundra flora dominated the Arctic during the Last Glacial Maximum, followed by regional divergence of vegetation during the Holocene epoch; (2) certain grazing animals consistently co-occurred in space and time; (3) humans appear to have been a minor factor in driving animal distributions; (4) higher effective precipitation, as well as an increase in the proportion of wetland plants, show negative effects on animal diversity; (5) the persistence of the steppe–tundra vegetation in northern Siberia enabled the late survival of several now-extinct megafauna species, including the woolly mammoth until 3.9 ± 0.2 thousand years ago (ka) and the woolly rhinoceros until 9.8 ± 0.2 ka; and (6) phylogenetic analysis of mammoth environmental DNA reveals a previously unsampled mitochondrial lineage. Our findings highlight the power of ancient environmental metagenomics analyses to advance understanding of population histories and long-term ecological dynamics