It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, May 17, 2025
Limited evidence for “escalator to extinction” in mountain ecosystems under climate change
Summary author: Walter Beckwith
American Association for the Advancement of Science (AAAS)
Mountain ecosystems may be more resilient to climate change than previously believed, according to a new study, which reports little empirical support for the widely recognized “escalator to extinction.” The findings challenge long-standing assumptions about range shift-driven extinction and instead introduce biotic homogenization as a more immediate concern facing mountain plants and animals. Mountain ecosystems worldwide are undergoing profound change due to rapid climate change. As temperatures increase, species are expected to shift their ranges upslope to take advantage of cooler habitats. However, while mountains offer vertical refuge for species adapting to climate change, their steep and confined topography limits how far some species can move, suggesting that climate warming may disproportionately threaten mountain biodiversity, especially species restricted to high elevations, narrow ranges, or tropical lowlands. This is sometimes described as the “escalator to extinction.” While some studies support this prediction, evidence remains inconclusive, especially for range shift gaps and lowland attrition. As such, the ecological consequences of climate warming in mountain regions are likely far more intricate than a uniform upward migration.
Using data from 8,800 records of historical and modern elevational range limits for over 2,000 animal and plant species across five continents, and a sophisticated Bayesian modeling approach, Chen et al. found little empirical support for predicted threats. Instead, the authors found that, despite ongoing climate warming, widespread range shift-driven extinctions in mountain ecosystems have not yet materialized. According to the findings, most species' elevational range shifts remain consistent with expectations shaped by the topographical constraints of mountain landscapes. Narrow-range species are expanding upslope without the hypothesized corresponding losses at their lower limits, countering previous assumed concerns about range shift gaps. Moreover, Chen et al. show that many lowland species are moving upslope without retreating from their lower boundaries, further challenging the prevailing view that tropical lowland species are confined to narrow thermal niches. One notable ecological signal the study revealed was growing biotic homogenization, wherein species communities across different elevations have become increasingly similar. This pattern, observed in several mountain regions, is likely driven by the upslope expansion of widespread lowland species alongside the decline of specialized, range-restricted taxa. According to the authors, this homogenization may foreshadow broader biodiversity losses and could disrupt ecological interactions in ways that reverberate through entire mountain ecosystems.
A large-scale genomic study of over 1,500 individuals from 139 underrepresented Indigenous groups across northern Eurasia and the Americas sheds new light on the ancient migrations that shaped the genetic landscape of North and South America. The results reveal distinct ancestry patterns and early diversification of Indigenous South American populations. The late Pleistocene saw the migration of humans from North Asia into North and South America beginning by at least 23,000 years ago, according to archaeological evidence. This expansion was rapid – genetic evidence suggests northern and southern Native American groups began diverging between 17,500 and 14,600 years ago, with human presence in southernmost South America confirmed by 14,500 years ago. However, many questions remain about this expansion and its impact on the genetic architecture of human populations across the continents, especially in South America, where high-resolution genomic studies are still lacking.
To address this knowledge gap, Elena Gusareva and colleagues developed a comprehensive, high-resolution genomic dataset comprising over 1,500 individuals from 139 ethnic groups – many previously unstudied. This dataset, containing more than 50 million high-quality genetic variants, was analyzed alongside ancient and modern DNA from Native American populations. This helped the authors investigate deep patterns of population history, migration, and adaptation. Gusareva et al. found that Siberian populations trace their ancestry to six ancient lineages, with West Siberian heritage broadly shared across the region. A notable population decline around 10,000 years ago may have been driven by climate change and the loss of megafauna. Moreover, genetic and archaeological evidence suggests that Native Americans diverged from North Eurasians between 26,800 and 19,300 years ago, with west Beringian groups like the Inuit, Koryaks, and Luoravetlans being their closest living relatives. In South America, four distinct Indigenous lineages – Amazonians, Andeans, Chaco Amerindians, and Patagonians – rapidly emerged from a common Mesoamerican origin between 13,900 and 10,000 years ago. The four lineages largely reflect distinct geographical and environmental regions, such as the Andes Mountains, the arid lowlands of the Dry Chaco, the humid tropical rainforests of the Amazon Basin, and the frigid polar climate of Patagonia. According to the authors, rapid geographic isolation of these groups likely reduced genetic diversity, particularly in immune-related HLA genes, which may influence susceptibility to infectious diseases.
Photo 1 (From left) - NTU and SCELSE researchers, comprising Research Fellow Dr Amit Gourav Ghosh, Senior Research Fellow Dr Elena S. Gusareva, Assoc Prof Kim Hie Lim, and Prof Stephan Schuster, with the advanced DNA sequencing machines in SCELSE.
An international genomics study led by scientists from Nanyang Technological University, Singapore (NTU Singapore) at the Singapore Centre for Environmental Life Sciences Engineering (SCELSE) and Asian School of the Environment (ASE) has shown that early Asians made humanity’s longest prehistoric migration.
These prehistoric humans, roaming the earth over a hundred thousand years ago, would have traversed more than 20,000 kilometres on foot from North Asia to the southernmost tip of South America.
This journey would have taken multiple generations of humans, taking thousands of years. In the past, land masses were also different, with ice bridging certain portions that made the route possible.
Supported by the GenomeAsia100K consortium [1], the study was published this week in Science, which analyses DNA sequence data from 1,537 individuals representing 139 diverse ethnic groups.
The study involved 48 authors from 22 institutions across Asia, Europe and the Americas.
The researchers traced an ancient migratory journey that began in Africa, proceeded through North Asia and ended at Tierra del Fuego in modern-day Argentina, which is considered the final boundary of human migration on Earth.
By comparing patterns of shared ancestry and genetic variations that accumulate over time, the team was able to trace how groups split, moved, and adapted to new environments.
These patterns allowed the team to reconstruct ancient migration routes and estimate when different populations diverged.
The reconstructed routes gave a detailed picture of how early humans reached the far edge of the Americas, and the findings suggested that this pioneering group overcame extreme environmental challenges to complete their journey across millennia.
A key insight was that these early migrants arrived at the northwestern tip of South America, where modern-day Panama meets Colombia, approximately 14,000 years ago.
From this critical point of entry, the population diverged into four major groups: one remained in the Amazon basin, while the others moved eastward to the Dry Chaco region and southward to Patagonia’s ice fields, navigating the valleys of the Andes Mountains, the highest mountain range outside of Asia.
By analysing the genetic profiles of indigenous populations in Eurasia and South America, researchers from the GenomeAsia100K project have, for the first time, mapped the unexpectedly large genetic diversity of Asia.
Understanding migration and genetic resilience
The study also sheds light on the evolutionary consequences of such a vast migration.
Associate Professor Kim Hie Lim from NTU’s Asian School of the Environment, the study’s corresponding author, explained that the arduous journey over thousands of years had reduced the genetic diversity of the migrant population.
“Those migrants carried only a subset of the gene pool in their ancestral populations through their long journey. Thus, the reduced genetic diversity also caused a reduced diversity in immune-related genes, which can limit a population’s flexibility to fight various infectious diseases,” explained Assoc Prof Kim, a Principal Investigator at SCELSE and Vice-Director of GenomeAsia100K.
“This could explain why some Indigenous communities were more susceptible to illnesses or diseases introduced by later immigrants, such as European colonists. Understanding how past dynamics have shaped the genetic structure of today’s current population can yield deeper insights into human genetic resilience.”
SCELSE Senior Research Fellow Dr Elena Gusareva, the study’s first author, said that these early groups settled into new ecological niches, and over hundreds of generations, their bodies and lifestyles evolved in response to the unique challenges of each region.
“Our findings highlight the extraordinary adaptability of early, diverse indigenous groups who successfully settled in vastly different environments. Using high-resolution whole-genome sequencing technology at SCELSE, we can now uncover the deep history of human migration and the genetic footprints left behind by the early settlers.”
Importance of Asian representation in genetic studies
NTU Professor Stephan Schuster, the study’s senior author of the paper and the Scientific Director of the GenomeAsia100K consortium, said: “Our study shows that a greater diversity of human genomes is found in Asian populations, not European ones, as has long been assumed due to sampling bias in large-scale genome sequencing projects.”
“This reshapes our understanding of historical population movements and lays a stronger foundation for future research into human evolution. Our new insights underscore the importance of increasing the representation of Asian populations in genetic studies, especially as genomics plays a critical role in personalised medicine, public health, and the understanding of human evolution,” added Prof Schuster, who is the President’s Chair in Genomics at NTU’s School of Biological Sciences, and the Deputy Centre Director at SCELSE.
By tracing the impact of migration and isolation on genetic characteristics, the study offers insights into how different populations respond to diseases and how their immune systems have evolved.
The findings also help scientists better understand the genetic makeup of Native American populations and help policymakers to better protect and conserve native communities.
It also demonstrates how advanced genomic tools and global collaboration can deepen humanity’s understanding of human evolution and inform future medical and scientific breakthroughs.
###
[1] GenomeAsia100K is a non-profit consortium focused on sequencing and analysing 100,000 Asian genomes to drive population-specific medical advancements and precision medicine. See website for more information.
Video of the research study by GenomeAsia100K, which analysed over 1,500 genomes from 138 Asian ethnic groups across 22 institutions. It found that early Asians made the longest-known prehistoric human migration, from North Asia to South America.
A new study combining Indigenous knowledge systems with Western genomics has uncovered how megafauna – namely ancient horses – were impacted during a period of substantial habitat change. During the late Pleistocene, the study reports, horses repeatedly migrated between North America and Eurasia, but after the Last Glacial Maximum, warming caused a land bridge to be submerged, severing this connection, and ultimately contributing to horses’ decline in North America. The findings could inform modern conservation approaches. Large animals, or megafauna, play critical roles in maintaining ecological balance. Their decline can lead to far-reaching disruptions for both natural and human communities. These risks are particularly pronounced in the rapidly warming Arctic. Indigenous scientific systems have long documented how shifts in climate reshape habitats. Complementing this, the fossil record offers a deep-time perspective on how local megafauna responded to past periods of rapid environmental change. Pleistocene-age horses in Beringia – a once-continuous landmass connecting Asia to North America – are a good model of megafauna so impacted. Still, despite dramatic environmental shifts during the Late Pleistocene, the effects on Beringian horse populations and their legacy remain poorly understood.
To trace how horses responded to environmental shifts over the past 50,000 years, Yvette Running Horse Collin and colleagues merged geochemical and genetic analyses of ancient Beringian horse fossils with Indigenous scientific protocols. Running Horse Collins et al. generated genomes from 67 ancient horse fossils found across Beringia, Siberia, and continental North America and analyzed them alongside data from all known horse lineages. They integrated their genomic data with radiocarbon dates and stable isotope measurements from fossil horse collagen. The findings reveal repeated trans-Beringian horse migrations between 50,000 and 13,000 years ago, with genetic exchanges occurring in both directions – from North America to Eurasia and vice versa. Some horse lineages in Eurasia, including fossils from northeastern Siberia and even as far west as Iberia, show traces of North American ancestry, supporting widespread dispersals. According to the authors, this complex genetic legacy mirrors the interconnectivity emphasized in Indigenous knowledge systems, which view life forms as deeply relational, not isolated. Moreover, the study also suggests that habitat changes due to warming and deglaciation at the Pleistocene-Holocene transition – particularly the shift from dry grasslands to wet, boggy tundra – limited horse mobility and food access, contributing to population decline in North America. In contrast, generalist herbivores such as moose and elk flourished.
These patterns underscore a broader ecological principle found in Indigenous science, particularly the Lakota concept of mitakuye oyasin, which emphasizes that a species’ survival depends not only on geography, but also its relationship with other life forms within a shared, interdependent habitat. Changes to this relational habitat can serve as the driving force for movement or migration.
For reporters interested in further insights into how this work was done, author Ludovic Orlando said, “Establishing collaborations with Indigenous scientists grounded in mutual respect and equal partnership is essential for the future of all scientific disciplines. Indigenous communities have cultivated deep and invaluable knowledge systems over countless generations. However, the structure of project-based science – often driven by tight funding cycles and publication deadlines – can pose challenges to meaningful cross-cultural dialogue and may not always align with Indigenous protocols for sharing traditional knowledge. The co-authors of this study have worked under the guidance of an Indigenous Review Board to ensure that every stage of the research – from study design to publication – respects and adheres to Indigenous protocols. We hope our approach can serve as a valuable model for other researchers and help foster broader adoption of ethically grounded, collaborative scientific practices.”
Recently, a joint Chinese–American research team led by Dr. HU Han from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and Dr Jingmai O’Connor from the Field Museum of Natural History (Chicago) announced the discovery and scientific description of the 14th known specimen of Archaeopteryx, known as the Chicago Archaeopteryx. Owing to its exceptional and exquisite preservation, the team was able to use advanced techniques like high-resolution CT scanning and 3D reconstruction to investigate the skeletal, soft tissue, and feather structures in unprecedented detail. Their findings provide crucial insights into the evolution of the skull and adaptations for flight during the critical transition from non-avian dinosaurs to birds. The study was published in Nature in May 2025.
Archaeopteryx is one of the most famous fossil animals in the world. Its discovery shortly after the publication of Darwin’s On the Origin of Species offered strong support for the theory of evolution. For more than 160 years, this enigmatic “first bird” has fascinated scientists and the public alike. However, due to the limitations of preservation and technology, many mysteries about this ancient animal have remained locked in the Solnhofen limestone where they were found. The newly described Chicago specimen, acquired by the Field Museum in 2022, is the smallest known Archaeopteryx, roughly the size of a pigeon. It is nearly complete, with many bones preserved in relatively three dimensions, and includes rare traces of soft tissues such as skin, toe pads, and feathers—making it a landmark specimen in the study of early bird evolution.
Thanks to the specimen’s exceptional preservation, the researchers successfully conducted high-resolution CT scanning and digital 3D reconstruction. The results reveal an almost completely preserved skull, including a remarkably intact palatal region. The palatal morphology of the Chicago specimen is intermediate between that of troodontids and more derived Cretaceous birds, representing a critical evolutionary stage in the transition from the rigid, immobile skulls of non-avian theropods to the lighter, more kinetic skulls of birds. In addition to providing new clues about Archaeopteryx, this reconstruction lays the groundwork for future biomechanical and functional analyses of fossil bird skulls. Beyond skeletal features, the study also documented preserved soft tissues. In particular, the shape of the toe pads resembles that of modern ground foraging birds, suggesting that Archaeopteryx was adapted for non-raptorial terrestrial locomotion. These findings support the idea that Archaeopteryx may have led a mixed lifestyle, spending time on the ground and possibly in trees, indicating a broader ecological flexibility than previously recognized.
Significantly, the Chicago Archaeopteryx is also the first Archaeopteryx known to preserve tertials, which attach to the humerus and ulna and occupy the space between the wing and the body. These feathers are thought to contribute to a continuous aerodynamic surface during flight. Since such structures have never been observed in any non-avian feathered dinosaur, their presence in Archaeopteryx suggests they may represent a flight-related innovation, highlighting the evolutionary step toward powered flight.
The Chicago Archaeopteryx also marks a step forward in the application of advanced technological methods in paleontology, especially in 3D scanning and reconstruction, soft tissue identification, and ecological inference for extinct bird lineages.
This study was supported by the National Natural Science Foundation of China.
