For immediate release: 9 June 2026
Peer-reviewed / Genetics / Biodiversity
WHY ARE SLOTHS SO SLOW? IT’S IN THEIR DNA
Sloths are the slowest mammals on the planet, but living in dense jungles has made them notoriously difficult to study. For the first time, scientists have now sequenced and analysed the two-toed sloth genome and revealed the genetics behind their extremely slow metabolism.
Building on work initiated at the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, researchers at the Wellcome Sanger Institute, IZW, Hospital Sírio Libanês in São Paulo, Brazil, and their collaborators sequenced and analysed the genome of a captive two-toed sloth. By mapping their evolution, they discovered sloth-specific ‘jumping genes’ that have been conserved over millions of years and are linked to the metabolism.
The results, published today (9 June) in BMC Biology , begin to uncover the genetics behind the sloth’s unique biology, and could lead to new research into metabolism-associated conditions and ageing in other mammals, including humans.
Along with armadillos and anteaters, sloths are members of Xenarthra, the only clade of placental mammals to have originated in South America. Xenarthrans have been around for 65.5 million years, with extinct sloth ancestors including elephant-sized giant ground sloths. Now, modern-day sloths are all tree-dwelling and belong to two groups – two-toed sloths and three-toed sloths 1 .
Sloths are the slowest of all mammals. They spend most of their time in the trees where they hang motionless and camouflaged, and when they do move between branches to feed on leaves and fruits – it all happens at a slow pace. Sloths have the lowest metabolism among mammals, often less than half of what is expected for their body size. To conserve energy, they can switch between self-regulating their body temperature, and allowing it to fluctuate with the environment, hovering around 5°C 2,3 . While being slow, they are surprisingly strong swimmers, sometimes swimming large distances when searching for a mate 1 .
To delve deeper into the unusual biology of sloths, IZW, Sanger Institute scientists and their collaborators turned to genomics.
Using samples from a captive sloth 4 , the team extracted DNA from the tissues, which was then sequenced at the Max-Planck Institute for Molecular Cell Biology & Genetics in Germany.
Sanger Institute and IZW researchers then analysed the sloth genome and compared the sequence to other mammal genomes, including an anteater and an armadillo, in a technique known as comparative genomics. This compares the genomes, or genetic ‘instruction manuals’ of different mammals to understand what makes sloths unique.
The scientists found that the sloth genome had several copies of active transposable elements, called ‘transposons’ or ‘jumping genes’, which are DNA sequences that can copy and paste themselves to change their position in the genome. Some transposons are still seen in the human genome, but are usually inactive, old and fragmented. Active transposable elements, however, create rearrangements in the chromosomes, which can lead to cancer in humans.
By using genomics to look back through time and map the evolution of sloths, the researchers found these ‘jumping genes’ arose in the last common ancestor of all surviving sloth species, around 30 million years ago. The genes have since been conserved over time, making them ingrained genetic sequences that are unique to sloths.
The team was surprised to find that many of these genes are connected to mitochondria – the ‘power houses’ of cells that generate their energy – and metabolic pathways. Since sloths have one of the most unique metabolisms among mammals, the researchers believe that these sloth-specific genes are related to their unusual adaptations to the environment and evolution of their extremely slow metabolism.
The next step is for the team to study these genes in more detail in cell lines, using lab experiments and single-cell sequencing to validate their function. They suggest that sloth cell lines could become a very good model to study metabolism-associated and age-related health conditions in mammals, including humans.
Dr Marcela Uliano-Silva, Senior Bioinformatician and co-lead author at the Wellcome Sanger Institute, said: “Evolution has already run billions of experiments. By studying unusual animals like sloths, we sometimes uncover biological solutions that humans never evolved. Using genomics to look back through time, we found ‘jumping genes’ that sloths have conserved over millions of years. These sloth-specific genes are linked to mitochondria and metabolic pathways, suggesting they might be related to the evolution of their extremely slow metabolism.”
Dr Pedro Galante, co-lead author at the Hospital Sírio Libanês in São Paulo, Brazil, said: “Many human conditions – including diabetes, ageing-related disorders, neurodegeneration, and muscle wasting – involve problems with energy production and mitochondrial function. While further research is needed, sloth cell lines may offer a natural model for understanding how organisms cope with low-energy states, and what goes wrong in disease. In the long term, this could inform research into tissue preservation, critical care medicine, ageing, metabolic disease, and even long-duration space travel.”
Dr Camila Mazzoni, co-lead author and Head of Evolutionary and Conservation Genomics at the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, said: “Sloths have the slowest metabolism of any mammal, yet they remain healthy. Understanding how they achieve this may reveal new insights into how cells manage energy efficiently. Our findings suggest that sloths might have evolved genetic ‘backup systems’ that help compensate for their ‘relaxed mitochondria’ and support their unique lifestyle.”
ENDS
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Emily Mobley
Press Office
Wellcome Sanger Institute
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+44 (0)7748 379849
Email: press.office@sanger.ac.uk
Notes to Editors:
Publication:
Marcela Uliano-Silva et al . (2026) ‘Elevated retrocopy burden and sloth-specific expansions illuminate mammalian genome evolution’. BMC Biology . DOI: https://doi.org/10.1186/s1291
5-026-02632-5
Funding:
This research was supported by Wellcome, the European Union’s Horizon 2020 research and innovation programme and the São Paulo Research Foundation.
Selected websites:
Leibniz Institute for Zoo and Wildlife Research (IZW)
The IZW is an internationally renowned German research institute whose goal is to understand how wildlife adapts to global environmental change, and to contribute to enhancing the survival of viable wildlife populations. To this end, we study the diversity of life histories, the mechanisms of evolutionary adaptations and their limits (including diseases), and the relationships between wildlife, their environment and people. Using an interdisciplinary approach that draws on expertise from biology and veterinary medicine, we conduct fundamental and applied research – from the molecular to the landscape level – in close dialogue with the public and stakeholders.
The Wellcome Sanger Institute
The Wellcome Sanger Institute is a world leader in genomics research. We apply and explore genomic technologies at scale to advance understanding of biology and improve health. Making discoveries not easily made elsewhere, our research delivers insights across health, disease, evolution and pathogen biology. We are open and collaborative; our data, results, tools, technologies and training are freely shared across the globe to advance science.
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BMC Biology