North America saved its bison from extinction. Now scientists face a new threat

For thousands of years, bison were among the defining animals of North America.

Long before cities, highways and farms transformed the continent, millions of the massive animals moved across the plains and woodlands from Canada to Mexico. For Indigenous communities, bison provided food, clothing, shelter, tools and other essentials, while also holding deep cultural and spiritual significance.

Today, the animals are no longer on the edge of extinction. About 530,000 bison are estimated to live across North America.


But a new study published in the journal Science suggests that saving the species from disappearing was only the first challenge. Researchers say the fragmented herds left behind by centuries of human intervention could gradually lose the genetic diversity they need to remain healthy and adaptable.

The study, produced by researchers involved in the Bison Integrated Genomics (BIG) Project, provides the most detailed picture yet of how bison genetics have changed over thousands of years.

Millions of bison once covered North America

American bison, commonly called buffalo, have been present in North America for roughly 200,000 years. Their ancestors crossed from Siberia into Alaska via the Bering land bridge and eventually spread across much of the continent.

Around 1,000 years ago, their population may have reached approximately 50 million animals.

Two major groups emerged: plains bison, which occupied much of the grasslands, and wood bison, which were found primarily in northwestern Canada.

Despite the enormous distances between herds, the new Science study found that bison remained remarkably similar genetically for thousands of years.

Researchers examined DNA from ancient remains and historical specimens and discovered that animals living thousands of kilometres apart were part of a highly connected genetic population.

That constant exchange of genes may have helped bison remain resilient through dramatic environmental changes.

The slaughter that nearly erased the species

The relationship between bison and humans changed dramatically after European settlement.

During the 19th century, commercial hunters killed bison on an extraordinary scale. The destruction was driven by demand for hides and other products, but the elimination of the animals also undermined Indigenous communities that depended heavily on them.

By around 1890, only about 500 bison remained.

The collapse created one of the most severe population bottlenecks in the species' history.

Yet bison survived.

Indigenous communities, ranchers, scientists, conservationists and government agencies eventually became involved in efforts to rebuild populations. One important source was a herd developed by Montana ranchers Michel Pablo and Charles Allard after bison calves were rescued in the 1870s.

Their herd eventually grew to hundreds of animals and helped supply bison for conservation programs, including efforts to restore populations in Yellowstone National Park and Canada's Elk Island National Park.

The surprising finding hidden in bison DNA

The new Science paper examines what happened genetically during that dramatic population collapse.

Researchers with the BIG Project sequenced whole genomes from 160 historical bison specimens and combined those results with 52 previously sequenced genomes. Some of the oldest remains examined were approximately 50,000 years old.

Scientists expected the 19th-century bottleneck to have dramatically reduced genetic diversity.

Instead, they found something unexpected.

Bison populations living before and after the near-extinction event retained remarkably similar levels of genetic diversity.

The explanation appears to lie in the genetic connectedness of bison across North America. Because the population was genetically homogeneous before the slaughter, the roughly 500 survivors collectively retained a surprisingly large share of the species' genetic variation.

It was a remarkable escape from what could have been a devastating genetic collapse.

The problem has shifted to isolated herds

The situation today is different.

Bison numbers have recovered, but the animals are divided into hundreds of relatively small and isolated populations. Most no longer have the opportunity to exchange genes naturally with distant herds.

The Science study warns that this fragmentation could gradually erode genetic diversity.

Scientists estimate that a herd may need roughly 1,000 animals to maintain healthy genetic diversity over the long term. Many existing populations fall well below that figure.

"If we continue with this system of fragmented populations, in 100 or 200 years, we can expect lots of inbreeding and a loss of genetic diversity," said Jaswant Singh, a reproductive scientist at the University of Saskatchewan.

The concern is not that bison are about to disappear again. Instead, scientists fear that isolated populations could become increasingly vulnerable to disease, environmental changes and other pressures over generations.

The cattle gene controversy is more complicated than expected

Bison conservation has another complicated genetic chapter: their history with cattle.

In the late 19th century, ranchers experimented with crossing bison and cattle. Some hybrids were fertile, allowing cattle genes to enter certain bison populations.

A 2022 study suggested that cattle ancestry might be present in every living bison.

The latest Science research offers a less alarming picture.

Of 45 modern bison genomes examined by the researchers, only about one-third showed evidence of cattle ancestry.

That indicates that cattle-bison genetic mixing is real but may not be as widespread as earlier research suggested.

The finding has also revived a difficult conservation debate: should scientists prioritize maintaining genetic "purity," or focus on preserving populations that are genetically diverse and resilient?

Some researchers argue that genetic health should ultimately matter more than eliminating every trace of historical cattle ancestry.

Scientists find another genetic twist in wood bison

The Science study also sheds new light on the relationship between plains bison and wood bison.

Researchers found that the two groups likely separated around 3,000 years ago, much earlier than some previous estimates.

Today, they share approximately 99.9% of their genomes, but their remaining differences are consistent enough for scientists to distinguish them genetically.

Human intervention later brought the two populations into much closer contact.

During the 1920s, Canadian officials moved thousands of plains bison into Wood Buffalo National Park after concerns about overcrowding elsewhere.

The two groups subsequently interbred.

The new study found plains bison ancestry in all 13 wood bison genomes it examined. That suggests the genetically distinct wood bison may no longer survive in completely pure form.

Some individual animals, however, carry relatively little plains bison ancestry and could potentially become important for future conservation efforts.

The next step: Build a genetic safety net

The researchers behind the Science study are now looking beyond population numbers.

The BIG Project wants to create a biobank of bison genetic material that could preserve genetic diversity from vulnerable populations and eventually help restore it to isolated herds.

The strategy would involve collecting sperm and eggs from genetically diverse wild bison and preserving them for future use.

That could be particularly valuable for small herds exposed to threats such as drought, wildfires, disease or extreme weather.

For the Athabasca Chipewyan First Nation, which helps manage the Ronald Lake bison herd, the idea has gained importance because the herd contains fewer than 400 animals.

"If there was a really bad season — drought, wildfires, disease — our whole herd could get wiped out," said Lori Cyprien, a land and resource manager with the First Nation.

A genetic bank could preserve material from the herd and potentially allow scientists to rebuild a genetically similar population if disaster struck.

IVF could help reconnect bison populations

Preserving genetic material is only half the challenge.

Scientists also need ways to move genes between isolated populations without transporting large numbers of live bison.

One possibility is in vitro fertilization, or IVF.

Researchers have adapted reproductive techniques used in cattle to bison, collecting eggs and sperm, fertilizing them in laboratories and implanting resulting embryos into other animals.

The first IVF bison was born at the University of Saskatchewan in 2016.

The technique remains difficult. Only around 10% of attempts result in healthy bison embryos, compared with roughly 30% in cattle.

Disease-control requirements add another complication because researchers must guard against illnesses including bovine tuberculosis and brucellosis.

Indigenous communities are central to the conservation effort

For Indigenous communities, bison conservation is about much more than genetics.

Bison have long been regarded as sacred animals by many Indigenous peoples, and their return is closely tied to cultural renewal and relationships with the land.

That makes Indigenous involvement essential as scientists develop new approaches to genetic conservation.

Some communities remain cautious about reproductive technologies and interventions, particularly when conservation efforts risk becoming too invasive.

But there is also growing interest in projects that could strengthen bison populations and help Indigenous communities reconnect with herds on their traditional lands.

Researchers involved in the BIG Project say the work must be conducted with respect for Indigenous knowledge, traditions and authority over the animals.

Bison's next fight is invisible

The history of the American bison has already gone through extraordinary extremes: from tens of millions of animals to only a few hundred, followed by one of conservation's most remarkable recoveries.

The new Science study shows that the species escaped the worst genetic consequences of its historic population collapse.

But it also highlights a different challenge.

The problem is no longer simply saving bison from extinction. It is ensuring that isolated herds retain enough genetic diversity to remain resilient for generations.

Scientists now hope that genetic sequencing, biobanking and assisted reproduction can help reconnect populations that have been separated for decades.

For Indigenous communities, the stakes are even greater. A healthy bison population represents not just a conservation success, but the continuation of a relationship with an animal that has shaped North American life, culture and identity for thousands of years.