A sloth genome looks nothing like the animal it came from. It is an immense sequence of DNA letters, assembled by computers from millions of smaller fragments. Yet hidden in that sequence are clues about ancestry, metabolism and the unusual biology that lets a sloth thrive at such an unhurried pace.
A new profile from the Wellcome Sanger Institute follows senior bioinformatician Dr Marcela Uliano da Silva, who helped lead a collaborative study of the Linnaeus's two-toed sloth genome. Her story offers a useful look behind the headline. Reading a genome is not one magic test. It is a chain of careful work involving animal care, tissue preservation, sequencing, computing and comparison with other species.
What is a reference genome?
A reference genome is a carefully assembled map of an organism's DNA. Scientists begin with DNA extracted from biological material, then sequencing machines read many pieces of it. Those pieces must be checked, overlapped and arranged into much longer stretches. A chromosome-level assembly aims to place those stretches in the correct large-scale order.
The finished reference does not describe every individual sloth. Like a map made from one route through a forest, it provides a reliable framework that other samples can be compared against. Better assemblies make it easier to locate genes, inspect chromosome structure and spot sections that were previously missing or misplaced.
The Vertebrate Genomes Project, which Uliano da Silva joined, aims to produce near error-free reference assemblies for roughly 70,000 living vertebrate species. Such a library can help researchers investigate evolution, specialised traits and genetic risks facing threatened wildlife.
Where did the sloth DNA come from?
Wild sloths are difficult to study because they spend much of their lives high in dense tropical forest. For the 2026 genome project, the team used preserved tissue from Lama Su, a two-toed sloth formerly housed at Tierpark Berlin. The sample was collected after the animal had been euthanised by veterinary staff for reasons unrelated to the study.
That detail matters. Genomic research depends on good records, responsible sample handling and cooperation between many institutions. The work described by the Wellcome Sanger Institute's research report involved scientists in Germany, the United Kingdom and Brazil, along with specialist sequencing and computational teams.
Sequencing is only the beginning
Once the DNA has been read and assembled, bioinformaticians examine it with software. They can compare the sloth sequence with genomes from related mammals, including anteaters and armadillos. This is called comparative genomics. Shared sections can point to deep ancestry, while differences may highlight changes that appeared along one evolutionary branch.
The researchers found an unusually large collection of retrocopies in the xenarthran genomes they examined. A retrocopy forms when an RNA copy made from a gene is copied back into DNA and inserted somewhere else in the genome. Many such copies do little. Some, however, can be retained through evolution and take on biological roles.
In the sloth study, several candidate copies were associated with parental genes involved in mitochondria and metabolic processes. Mitochondria help cells manage energy, so the finding is intriguing in an animal famous for an exceptionally low metabolic rate.
Did scientists find a single slowness gene?
No. Complex animals are not controlled by one tidy switch labelled “slow”. The genome study identified promising genetic clues, not final proof that a particular DNA change causes sloth slowness.
The team wants to test the candidates in cell lines and through further laboratory and single-cell work. Those experiments are needed to establish what the sequences actually do. Until then, the careful conclusion is that the genome has revealed possible links to the evolution of sloth metabolism.
This is a good example of science moving in stages. A high-quality reference genome lets researchers ask better questions. Comparative analysis produces candidates. Functional experiments then test whether those candidates behave as expected.
The people behind the sequence
Uliano da Silva's route into genomics began in Brazil, where she studied biology and later worked on the invasive golden mussel. She moved from laboratory research into bioinformatics, then joined sloth genome work at the Leibniz Institute for Zoo and Wildlife Research before continuing at the Sanger Institute.
In her September 2026 Sanger profile, she also discusses the need for genomics to grow more fairly. Much of the world's biodiversity is found in the Global South, but sequencing infrastructure and research funding are unevenly distributed. She argues for training, local capacity and genuine partnership rather than simply moving samples abroad without properly involving local scientists.
That principle is especially relevant to sloths. Living sloth species are native to Central and South America, so the expertise, institutions and communities within those regions should be central to research about them.
What can a genome do for sloth conservation?
A genome does not reconnect a broken canopy or insulate a dangerous power line. Those practical protections remain essential. Genomic tools answer a different set of questions. They can help researchers examine population relationships, genetic diversity and the evolutionary history of specialised traits.
The most useful conservation science combines tools rather than treating one as a miracle solution. Field observations reveal how sloths use real landscapes. Tracking shows where animals move and encounter hazards. Veterinary knowledge supports rescue and rehabilitation. Genomics adds a deeper biological map that can be revisited as new questions arise.
A slower animal, and a faster-growing field
The irony is appealing: one of the world's slowest mammals is helping to push a fast-moving area of science forward. Behind every polished genome lies years of preparation, technical work and collaboration.
For sloth lovers, the lesson is not that DNA has explained everything. It is that the closer scientists look, the more interesting sloths become. Their genomes preserve an evolutionary story written over millions of years, and researchers are only beginning to learn how to read it.
Sources and further reading
- Wellcome Sanger Institute Blog: Sloths, sequencing and South America
- Wellcome Sanger Institute: Why are sloths slow? It's in their DNA
- Vertebrate Genomes Project
Featured image: Marcela Uliano da Silva / Wellcome Sanger Institute. Image supplied on the official Wellcome Sanger Institute profile.