Map showing the locations and sample sizes of sites from which yak X genomes were generated. Extant wild yak distribution is in light orange.16 Elevation is shown. Map not to scale.
For young-Earth creationists, the problem with ancient DNA is that it keeps revealing histories which their preferred chronology cannot accommodate. The latest example is an extinct relative of the yak whose evolutionary separation from living yaks began at least 400,000 years ago — long before the supposed “Creation Week” of a literal reading of Genesis. Its existence has emerged from fragments of Siberian bone too incomplete to identify by their shape, but which retained something much more informative: genetic evidence of a lost branch of the bovine family tree.
In a study published in Current Biology, Jonas Oppenheimer, Alexandre Gilardet and colleagues report 20 ancient nuclear genomes from Denisova Cave and other sites in southern Siberia, spanning more than 200,000 years. The lineage, provisionally known as “yak X”, had previously been recognised from mitochondrial DNA. The new analysis provides much broader genetic evidence that it represented a distinct species that effectively separated from the lineage leading to living yaks by about 250,000 years ago.
This was no static population inhabiting an unchanging world. The genomes reveal a demographic decline and suggest population turnover, accompanied by reduced genetic diversity, around the last interglacial, approximately 130,000–115,000 years ago. Warming may have disrupted the distribution of these cold-adapted animals; an earlier warm interval may also have helped isolate populations during their initial divergence. Those climatic explanations remain hypotheses, but the genetic evidence provides a record against which they can be tested. The youngest specimen analysed is about 27,000 years old; precisely when, and why, the lineage subsequently disappeared remains unknown.
There is an equally instructive lesson in the researchers’ caution. Although they interpret the genomic evidence as identifying a separate species, they have not simply attached a new formal species name to these fragmentary remains. Comparisons with previously described yak-like fossils are needed to establish whether the genetic lineage corresponds to an animal already recognised from its anatomy. Discovering a previously unrecognised genetic history and resolving its taxonomic identity are related but distinct tasks. Scientific confidence in one does not require pretending that the other has already been settled.
For creationism, meanwhile, calling the animal “just another member of the cattle kind” does nothing to resolve the chronological problem. The evidence concerns a branching history of populations, divergence and eventual extinction extending across hundreds of thousands of years. Evolutionary biology supplies the framework for reconstructing that history and asking further questions about it. Compressing everything into a few thousand years would require an alternative explanation for the genetic relationships, the ages of the remains and the succession of populations — not merely a biblical label applied after the evidence has been collected.
Background^ The Evolutionary History of Yaks. Yaks are specialised members of the cattle family, adapted to the cold, thin air of the Tibetan Plateau and surrounding highlands. Their history combines ancient evolutionary divergence, changing Ice Age environments, natural selection and, much more recently, domestication and interbreeding with cattle.The Paper in Current Biology was supplemented by a Stockholm University account of the research:
An ancient branch of the cattle family
Yaks belong to the Bovini, the group that includes cattle, bison and buffaloes. Genetic studies place them particularly close to bison within the broader cattle radiation. They did not evolve from modern domestic cattle: the two lineages share much older ancestors. A 2012 analysis of the yak genome estimated the yak–cattle divergence at approximately 4.9 million years ago. Such dates depend on the genetic data, evolutionary models and calibrations used, so they should be treated as estimates rather than exact anniversaries.
A wider Ice Age distribution
The present distribution of wild yaks does not represent the full geographical history of their relatives. Pleistocene yak-like remains are known from regions north of the Tibetan Plateau, including southern Siberia. Establishing exactly how these fossils relate to living yaks is difficult, particularly when the remains consist of incomplete bones.
Ancient DNA is now helping to resolve that uncertainty. The extinct Siberian lineage known as “yak X” began diverging from living yaks at least 400,000 years ago. It represents a separate branch of the yak family tree, rather than an established direct ancestor of modern yaks. Its discovery shows that the diversity of yak relatives was once greater than the surviving animals alone would suggest.
Evolution in cold, oxygen-poor environments
Yak adaptations include their insulating coat and physiological characteristics that support life at high altitude. Genome research has identified evidence of selection affecting biological pathways involved in responses to low oxygen and the processing of nutrients. These findings help explain how ancestral populations became adapted to environments where cold, limited oxygen and seasonal food shortages impose strong pressures on survival and reproduction.
These adaptations did not arise because ancestral yaks anticipated mountain life. Heritable variants that improved reproductive success under local conditions could become more common over successive generations. Changing climates also altered the habitats available to yak populations, influencing their distribution, isolation and opportunities to meet again.
Wild yaks and domestication
The wild yak is generally called Bos mutus, while the domestic form is called Bos grunniens. Despite these different scientific names, domestic yaks descend from wild yak populations; their domestication is a comparatively recent episode within a much older evolutionary history.
The precise timing remains uncertain. A 2015 genomic study inferred domestication approximately 7,300 years ago under its preferred demographic model. More direct evidence comes from archaeological remains and ancient DNA from Bangga, on the southern Tibetan Plateau, demonstrating domestic yaks and yak–cattle hybridisation about 2,500 years ago. These dates measure different things: a modelled population history and a securely documented archaeological occurrence. The latter does not establish when domestication first began.
A family tree with reconnecting branches
Yak and cattle evolution has not involved complete, permanent genetic separation. Interbreeding followed by further reproduction can transfer DNA between their populations, a process called introgression. A 2018 genomic study identified yak-derived variants in Tibetan cattle, including genes involved in responses to low oxygen, which probably helped those cattle adapt to high altitude. Genetic material has also moved from domestic cattle into yaks.
This is an example of reticulated evolution: populations diverge, but some branches subsequently exchange genetic material. It does not mean every related lineage interbred extensively. The new yak X study found negligible evidence of gene flow with the steppe bison and aurochs that shared its wider region.
The overall picture: yaks are surviving representatives of an ancient and formerly more diverse evolutionary radiation. Their history includes adaptation, population separation, occasional genetic exchange, domestication and the extinction of relatives — with further details still being recovered from ancient bones.
Previously unknown extinct bovine species discovered in Siberia
DNA analyses of ancient remains have revealed a previously unknown extinct bovine species that inhabited southern Siberia during and even before the last Ice Age. The extinct species was related to modern yaks, but followed a separate evolutionary path for hundreds of thousands of years. The findings are published in Current Biology.
This is a remarkable discovery of a large extinct species based on small non-diagnostic bones.
Professor Love Dalén, senior author.
Centre for Palaeogenetics
Stockholm, Sweden.
The discovery was made from remains found in Denisova Cave and other sites in southern Siberia. By analysing ancient DNA from unidentifiable bone fragments, researchers from the Centre for Palaeogenetics in Stockholm, the University of California, Santa Cruz, and the University of Vienna generated 20 ancient genomes spanning 200,000 years.
Comparisons with other bovine genomes showed that the fossils belonged to a previously unknown species. The researchers estimate that it began diverging from modern yaks around 400,000 years ago and became fully separated around 250,000 years ago.
A useful comparison for when this lineage originated is the divergence between brown bears and polar bears, which has also been estimated to have occurred around 400,000 years ago. This age overlaps with a particularly strong warm climatic period, which could have prompted population isolation and, ultimately, speciation.
Alexandre Gilardet, co-lead author.
Centre for Palaeogenetics
Stockholm, Sweden.
A region of remarkable discoveries
An earlier study on trace amounts of DNA had suggested something special about some of the bone fragments found in and around Denisova Cave. The discovery also has a notable parallel in the same region.
One of the bone fragments that resulted in a genome, shown to scale in a hand at different angles or next to a 0,5 euro coin, at the Centre for Palaeogenetics in 2026.Photo: Dr Mário Vicente.These findings mirror the discovery of the Denisovans, a group of archaic humans, from a single fossil in 2010 and highlights the Altai region as a possible biodiversity hotspot and refugium across Ice Ages.
Professor Love Dalén.
However, in contrast to the hybridization observed among different ancient humans, the scientists detected negligible evidence for interbreeding between this new species and other bovines in the area, such as steppe bison or aurochs, the extinct wild ancestor of cattle.
Population changed during a warmer period
The results also suggested that a population replacement occurred during the last interglacial warm period, accompanied by a loss of genetic diversity.
This could reflect the genetic consequences of climate warming around 120,000 years ago on a cold-adapted species. The long time span of our dataset is really rare in ancient DNA, and allows us to look across whole glacial cycles to see how they might have impacted biodiversity.
Dr. Jonas Oppenheimer, co-lead author.
Centre for Palaeogenetics
Stockholm, Sweden.
The youngest specimen analysed is around 27,000 years old. The species became extinct sometime after that, but the exact timing and causes remain unknown.
Further research needed to classify the species
The extinct relative of modern-day yaks was detected at Denisova Cave and in the broader Altai-Sayan Mountains and southern Siberian region. In contrast, modern wild yaks are nowadays restricted to higher elevations of the Tibetan Plateau. Genetic evidence alone is not sufficient to formally classify and name a new species. Going forward, the researchers therefore plan to compare the findings with previously described yak-like remains from the region to determine whether they belong to the same species.
Publication:
What emerges from these fragments of ancient bone is a history of evolutionary divergence, changing populations and eventual extinction, extending across hundreds of thousands of years. Even the youngest specimen analysed, at approximately 27,000 years old, predates the entire history of Earth imagined by young-Earth creationists. Calling these animals members of a cattle “kind” does nothing to explain away that chronology or the genetic evidence of their relationships. A label is not an alternative scientific explanation.
The theory of evolution was central to interpreting these findings. Comparisons between genomes enabled the researchers to reconstruct relationships, estimate divergence times and investigate changes in genetic diversity. There was no need to invoke a supernatural intervention, nor any indication that evolutionary biology was inadequate to the task. The discovery adds a previously unrecognised branch to the bovine family tree; it does not require a different explanation for why such a tree exists.
Equally revealing is the distinction between what the researchers conclude and what they leave unresolved. The evidence supports a distinct evolutionary lineage, but its formal taxonomic identity still requires investigation. Climatic changes offer plausible explanations for aspects of its population history, but their precise role remains uncertain, as do the timing and cause of its extinction. These qualifications strengthen the account by making clear which conclusions are supported and which questions remain open.
This is how scientific knowledge advances: an incomplete picture becomes more detailed as new evidence becomes available. Creationism begins with a prescribed history and demands that the evidence fit it. Science allows ancient bones and their surviving DNA to reveal a history nobody had thought to prescribe — in this case, another lost chapter in the long, unplanned evolution of life.
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