Why Did the Woolly Mammoth Go Extinct?

Perhaps the most iconic extinct species, the woolly mammoth last roamed Earth around 4,000 years ago on the remote Wrangel Island in the East Siberian Sea. While the species once ruled the expansive mammoth steppe — the Pleistocene epoch’s largest ecosystem spanning Eurasia into North America — around 10,000 years ago, the woolly mammoth largely vanished from its range. Today, Colossal Biosciences is painstakingly working on the de-extinction of the woolly mammoth. But what caused its devastating extinction in the first place?

The mammoth’s extinction has long been a hotly debated topic, as its disappearance closely corresponds to both the end of the ice age and the proliferation of early modern humans. After over 100 years of discussion, the reality of the woolly mammoth’s extinction remains unclear, but several hypotheses continue to fight for scientific consensus. 

A Mammoth Meeting

Given the profound impact that humans continue to have on the local environment, the activities of our early modern counterparts are often the first to be blamed for the woolly mammoth’s extinction. 

Evidence has pointed to early modern humans hunting large species like the woolly mammoth, with early dwellings often constructed from mammoth skeletons and premature hunting tools like Clovis points frequently found alongside the remains of preserved megafauna. 

With a recent study from the University of Fribourg in Switzerland, scientists have shed light on exactly how impactful these early hunter-gatherers were upon the mammoth’s disappearance. Using an artificial intelligence model, this study utilized historical and fossil data for 2,118 proboscidean species like elephants, mastodons, and mammoths going back 35 million to 10,000 years in age. 

By feeding the system 17 physiological and environmental factors that potentially impacted the mammoth’s survival, the model determined the likelihood of each factor upon causing extinction, finding that proboscidean extinction rates rose fivefold shortly after the arrival of early modern humans.

Juan Cantalapiedra, an evolutionary paleobiologist at the National Museum of Natural Sciences in Madrid and co-author of the study, told ABC News that it’s likely hunting was one of the biggest contributions to the decline and annihilation of proboscidean species.

These findings are similar to a study from South Australia’s University of Adelaide, which used a computer model to track historical changes in the distribution and demography of the woolly mammoth fossil record in Eurasia to determine the impacts of human arrival, observing that in certain regions of Eurasia, humans accelerated the mammoth’s extinction by as much as 4,000 years.

“Our research shows that humans were a crucial and chronic driver of population declines of woolly mammoths, having an essential role in the timing and location of their extinction,” said the lead author of the study, Damien Fordham, associate professor at the Environment Institute at the University of Adelaide.

A Mammoth Metamorphosis

While humans almost certainly played a role in the woolly mammoth’s extinction, the impacts of the late Pleistocene epoch’s environmental changes cannot be underestimated.

As the last ice age ended around 10,000 years ago, the Earth’s glaciers began to melt, resulting in a gradual 11-degree Fahrenheit increase in global average temperatures by the 20th century. For the woolly mammoth, which thrived on the permafrost grasslands of the mammoth steppe, this change was quite dramatic, with some scientists arguing that it was likely too intense for the species to bounce back from. 

In a 10-year study out of St John’s College, University of Cambridge, England, scientists used genomic sequencing techniques to analyze Arctic plant and animal remains collected from 535 permafrost and lake sediment samples preserved from the period of the mammoth’s extinction. 

By mapping changes in aspects like animal distributions and floristic compositions, this study determined that as the climate became warmer and wetter, much of the mammoth steppe was rapidly transformed from grasslands into forests and shrublands, introducing vegetation unfamiliar and unpalatable to the woolly mammoth. 

“When the climate got wetter and the ice began to melt it led to the formation of lakes, rivers, and marshes. The ecosystem changed and the biomass of the vegetation reduced and would not have been able to sustain the herds of mammoths. We have shown that climate change, specifically precipitation, directly drives the change in the vegetation — humans had no impact on them at all based on our models,” said Yucheng Wang, Ph.D., lead author of the study and a research associate at the Department of Zoology, University of Cambridge.

This suggests that the small pockets of mammoth populations that survived for additional centuries in areas like Wrangel Island, Russia, and St. Paul Island, Alaska, thrived due to the relative geographic isolation of these areas, making them less susceptible to climate and vegetation changes.

“Wrangel Island was a golden place to live,” Stockholm University geneticist Love Dalén said in a New York Times article on the topic.

A Mammoth Mishap

While most opinions have landed on the woolly mammoth being taken out by either human predation, climate change, or a mixture of the two, the question remains of what led to the species extinction in areas like Wrangel Island, where it faced no predators and minimal rates of climate change. 

Although a colony of mammoths survived on the island the size of Delaware for up to 6,000 years after its mainland extinction, given the species’ small population on the island — which at one time was limited to merely eight breeding individuals — evidence suggests that it suffered from a severe genetic bottleneck, with consequences of inbreeding leading to high levels of inherited disease and unfavorable mutations.

While this had an undoubtedly devastating impact on the species, hundreds of inbred individuals were able to survive for generations within Wrangel Island’s uniquely favorable ecosystem, making it unlikely that this bottleneck was the direct cause of the species’ local extinction. 

Instead, experts believe this lack of genetic diversity likely left the mammoth at a greater risk of unexpected extinction events like viral epidemics, storms, and volcanic eruptions that wielded the final blow to the species.

“It was probably just some random event that killed them off, and if that random event hadn’t happened, then we would still have mammoths today,” said Dalén, who made these findings when conducting a comparative genomic analysis of mammoths found on Wrangel Island to those found on mainland Siberia. 

“Extinction, at least when it’s not at the hands of humans, doesn’t usually result from just one cause,” observed University at Buffalo biologist Dr Vincent Lynch, who was not involved in the study. “It’s the result of a combination of factors like inbreeding, a small population size, an accumulation of harmful mutations, and sometimes, bad luck.”

A Mammoth Mystery

Considering that the majority of woolly mammoths have been gone for 10,000 years, it’s uncertain that we’ll ever know the exact circumstances behind the icon’s untimely demise. While the mammoth’s extinction will likely remain a highly contested topic, with Colossal Biosciences making significant strides toward the de-extinction of the species, the mystery may soon become insignificant.