How the woolly mammoth, ambassador of the ice age, found himself trapped in modern Wrangel … [+]
Rising sea levels about 10,000 years ago turned Wrangel Island into a final refuge for woolly mammoths, isolating them from their mainland counterparts. As the world’s climate continued to warm and habitats changed, Wrangel Island became one of the last viable habitats for these mammoths to survive, setting the stage for their final chapter.
Four millennia ago, Wrangel Island was a frozen refuge, the last icebox where mammoths roam … [+]
The prevailing theory about the extinction of isolated populations, such as woolly mammoths on Wrangel Island, often points to inbreeding. Inbreeding can reduce the genetic variability of a population and increase the spread of deleterious genetic mutations, leading to reduced survival and reproductive rates. A notable example is the Tasmanian tiger, or thylacine, which suffered from reduced genetic diversity due to heavy inbreeding before its extinction in the 20th century.
However, this popular theory of inbreeding leading to extinction may not hold true for woolly mammoths from Wrangel Island, according to a June 2024 article published in Cell.
The event was a “bottleneck” but the mammoth was well on its way to recovery
The study analyzed 21 genomes of Siberian woolly mammoths and found that while the mammoth population experienced a significant bottleneck — an event that greatly reduces population size and genetic diversity — it recovered well. In the case of woolly mammoths on Wrangel Island, a critical event occurred when rising sea levels and a changing climate caused their numbers to decline significantly as they became isolated on the island.
This drastic reduction in population size has limited their genetic diversity and may have made them more sensitive to environmental stresses and changes.
The study found that while the population of mammoths on Wrangel Island started with just eight individuals, it grew to around 200 to 300 and remained stable until their extinction. Over time, the worst genetic mutations became less common as mammoths with these deleterious traits were less likely to reproduce.
This suggests that, contrary to expectations, inbreeding did not lead to the accumulation of deleterious mutations that could cause them to become extinct. Instead, an isolated population of mammoths was able to purge these deleterious mutations over generations, challenging the traditional view that genetic degradation was a key factor in their demise.
Did we have anything to do with extinction?
New genetic data on mammoths suggests that inbreeding was just one small part of a bigger storm brewing. While mammoths faced genetic challenges due to their isolation, the real threats to their survival likely came from a combination of known and unknown environmental changes and, quite possibly, human intervention.
The last wave of mammoths became extinct 4000 years ago. Around this time, human civilization advanced technologically and expanded geographically. The first humans reached various remote parts of the world, including areas near Wrangel Island.
This period marked significant changes in human hunting practices and land use that could have profound effects on local ecosystems. Although direct evidence that humans hunted the last mammoths on Wrangel Island is still elusive, the concordant timelines suggest that human activity may have played a role in stressing the mammoth population, either through direct hunting or habitat alteration.
This hypothesis is consistent with broader patterns observed in other species extinctions, where human expansion and environmental impact have often been critical factors. A similar scenario played out with the Tasmanian tiger, which faced relentless hunting, habitat loss due to agricultural expansion and disease introduced by invasive species. The combination of these factors led to the problem of inbreeding and subsequent extinction.
The dodo bird is another example of human-caused extinction. The dodo is from Mauritius and was not used to predators, so it was vulnerable when humans arrived. The introduction of invasive species, habitat destruction and outright hunting by sailors drove the dodo to extinction in the late 17th century.
The dodo bird, once a native of Mauritius, became prematurely extinct due to human activity … [+]
In both cases, as with mammoths, it was not just one factor, but a combination of human impacts and environmental changes that led to their extinction. Only time will reveal the details of how the last wave of mammoths to roam the Earth ended, but finds like these put things in perspective. They remind us that most species are resilient, built to withstand various challenges. It often takes a series of unfortunate events before a species actually becomes extinct.