Arctic animals evolved in different ways to beat the cold

Across the wind-swept tundras of the Arctic and the icy plateaus of Eurasia, a handful of remarkable creatures defied extinction. These animals, from woolly mammoths to arctic foxes, were not born into the cold – they became its masters.

But how exactly did they gain their thick fur, compact bodies, and resilience against subzero temperatures?

In a recent study, scientists traced the evolutionary paths that led to these remarkable adaptations. Drawing on fossil evidence and ancient DNA, they uncovered how glacial cycles shaped life over the past three million years.

The results offer a detailed picture of how cold-adapted animals and plants came to exist – and what that means in a rapidly warming world.

This new understanding could help predict which species might survive today’s climate shifts and which may vanish forever.

Two periods of cold evolution

The evolution of Arctic animals and other cold-adapted species was not a single event but unfolded in two sweeping phases. The first began between three and two million years ago, during the Late Pliocene and Early Pleistocene.

This is when early forms of mammals such as mammoths, reindeer, and musk oxen emerged. These species likely began their adaptations as the Earth cooled and ice sheets began forming more consistently at the poles.

The second, more critical phase began with the Middle Pleistocene Transition, roughly 700,000 years ago. During this time, the planet’s glacial periods grew longer and harsher.

Many of the cold-weather specialists we know today – such as the woolly rhinoceros and true lemmings – appeared during or shortly after this period.

The researchers found that some of these animals, like early mammoths, might have lived in both cold glacial periods and warmer interglacials. Their flexible nature likely gave them a starting point for the more specialized traits that followed.

When Arctic animals gained cold traits

Until recently, much of what we knew about these creatures came from bones and teeth. Today, ancient DNA – or aDNA – has added a powerful new tool to the field. This molecular evidence helps determine not only when a species appeared but also when specific cold-adapted traits evolved.

“This is the first concerted effort to compare the evolution of cold-adapted animals and plants since modern methods of palaeogenetics appeared,” Professor Stewart said.

The study showed that woolly mammoths already had many cold-related genes one million years ago, well before their full physical transformation. Later developments, such as changes to their hair, metabolism, and ear size, appeared closer to 700,000 years ago.

Similarly, DNA from ancient lemmings shows a burst of new species as recently as 100,000 years ago. The Norway lemming, for example, is among the youngest known mammalian species.

These findings illustrate how even in the later stages of the Ice Age, evolutionary change continued to shape species in profound ways.

Arctic animals adapted in different ways

The paper identifies three main theories for how species adapted to frigid environments, each supported by both fossil and genetic data.

Some animals, like the polar bear and woolly mammoth, may have moved northward from warmer zones and adapted after encountering the cold. This is known as the “out of the temperate zone” theory.

Others, like the reindeer and arctic fox, appear to have evolved directly in the Arctic. According to this “evolving in situ” theory, these species developed traits gradually as the northern climate cooled around them.

A third path, known as “montane preadaptation,” suggests that animals evolved in high-altitude regions like the Tibetan Plateau before migrating north. This might explain the origins of the woolly rhinoceros and the Arctic fox, whose ancestors lived in cold mountainous areas long before reaching polar latitudes.

These varied routes show that cold adaptation did not follow one script. Instead, it depended on local geography, climate patterns, and the traits a species already possessed.

Arctic plants tell a subtler story

While animals like the mammoth evolved visibly, Arctic plants followed a different trajectory. Most living Arctic plant species appeared in the last two million years, with many arriving from southern alpine or boreal zones. A small number evolved in place through hybridisation or chromosome duplication.

Dispersal played a bigger role than mutation. The largest genetic study of Arctic flora found that species more often moved into the Arctic than evolved there.

Western North America, the Himalayas, and the Asian steppe were major source regions. Yet despite these movements, Arctic plant species today show remarkably little endemism – only around 5 percent are unique to the region.

Researchers also found that while no large-scale extinctions were previously documented, recent DNA from sediments suggests some losses did occur.

Still, most Arctic plants proved resilient, thanks to their ability to reproduce asexually, survive with few resources, and carry multiple sets of chromosomes that store useful traits.

Beetles seem unchanged – but are they?

Beetles represent another piece of the Arctic puzzle. Their fossils suggest remarkable stability. Many modern species were already present over 2.6 million years ago, leading scientists to believe they barely changed during the Ice Age.

But this may not be the whole story. One study of ancient sedimentary DNA found beetle communities in northern Greenland that have no modern equivalent. This suggests that some beetles did adapt or vanish, but their changes were too subtle to see in fossil form.

Unlike mammals, beetles don’t show obvious structural changes. Their evolutionary shifts might lie in internal traits, such as metabolic processes or reproductive strategies – areas that ancient DNA is only just beginning to reveal.

What assembled the modern Arctic ecosystem?

Despite the rich fossil and genetic records, one major question remains: when did today’s Arctic ecosystem truly come together?

The study suggests that between 2.6 and 1.8 million years ago, the Arctic featured a mix of boreal, temperate, and extinct species, including early arctic animals – nothing like the ecosystems we see now.

It wasn’t until after 700,000 years ago that species like the woolly mammoth, reindeer, and arctic fox began to dominate. This suggests a relatively recent origin for the modern tundra environment.

“The cold-adapted species are amongst the most vulnerable animals and plants to ongoing climate change. Therefore, an understanding of how species evolved in the past is essential to help us understand the risks faced by endangered species today,” explained John Stewart.

By identifying where, when, and how these species evolved, scientists can now better predict which species are most at risk. It also helps conservationists decide how to protect them, whether by preserving habitat, guiding migration, or even using gene banks.

Arctic animals help us prepare for future

The Ice Age was not just a time of frozen landscapes – it was a crucible of evolution. Today’s cold-weather survivors carry the legacy of countless trials, migrations, and adaptations.

Their story, now sharpened by genetic science, reveals the astonishing power of evolution to shape life in the harshest places on Earth.

“We can now build on these findings to understand more about how more cold-adapted species evolved and how the Arctic ecologies arose in the past and use this to help conservation efforts in the future,” Professor Stewart concluded.

As the world warms, the past may offer the clearest guidance yet. The secrets buried in ancient genomes could be the key to helping life on Earth survive what comes next.

The study is published in the journal Trends in Ecology & Evolution.

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