Sloths, along with armadillos and anteaters, are classified under the genus Xenarthra, the sole group of placental mammals native to South America. In a groundbreaking study, researchers sequenced and analyzed the chromosomal-level genome of Linnaeus’s three-toed sloth (Choloepus didactylus) and the Southern anteater (Tamandua tetradactyla). They discovered unique genetic elements linked to energy production in sloths, shedding light on why these creatures possess the slowest metabolism of any mammal.
Linnaeus’s three-toed sloth (Choloepus didactylus) at London Zoo. Image credit: Dick Culbert / CC BY 2.0.
Xenarthrans have existed for approximately 65.5 million years, with ancestors that include giant, elephant-sized sloths.
All contemporary sloths reside in trees and are categorized into two main groups: the three-toed sloths and the two-toed sloths.
These creatures spend the majority of their time in trees, utilizing their camouflage by hanging still. When they forage for leaves and fruits, their movements are slow and deliberate.
Remarkably, sloths have the lowest metabolism of any mammal, often generating less than half of what their body size would suggest.
To conserve energy, sloths can choose between maintaining a stable body temperature or allowing it to vary with their surroundings.
Despite their slow pace, sloths are surprisingly proficient swimmers, capable of covering significant distances underwater when seeking a mate.
To better comprehend the unique ecology of sloths, Marcela Uliano Silva and her team at the Wellcome Sanger Institute utilized genomic analysis.
“There are already billions of experiments in evolution,” stated Dr. Uliano Silva.
“By investigating unique species like sloths, we occasionally uncover biological solutions that humans may not have developed.”
“Our genomic studies revealed a ‘jump gene’ that sloths have preserved for millions of years.”
These sloth-specific genes are linked to mitochondria and metabolic pathways, indicating their potential role in the evolution of the sloth’s extremely slow metabolism.
In this research, the authors sequenced and analyzed the genomes of both Linnaeus’s three-toed sloth and the southern anteater.
The findings indicated that the sloth genome contains numerous copies of active transposable elements known as “transposons” or “jumping genes.” These are DNA sequences capable of replicating and relocating within the genome.
By employing genomic analysis to trace back sloth evolution, researchers determined that these “jump genes” originated from the last common ancestor of all extant sloth species around 30 million years ago.
This gene has been conserved through time, eventually becoming part of sloth-specific genetic sequences.
Researchers were intrigued to discover that many of these genes are associated with mitochondria, which are the energy-producing “powerhouses” of cells, as well as metabolic pathways.
Given that sloths exhibit the most unique metabolism among mammals, these sloth-specific genes may play a pivotal role in their distinctive adaptation to their environment and the evolution of their slow metabolism.
“Even though sloths boast the slowest metabolism of all mammals, they maintain good health,” says Dr. Camila Mazzoni, a researcher at the Leibniz Zoo and Wildlife Institute and the Berlin Center for Biodiversity Research and Genomics.
“Understanding how their cells achieve this could yield new insights into energy management at the cellular level.”
“Our findings imply that sloths may have developed a genetic ‘backup system’ to offset their ‘relaxed mitochondria’ and sustain their unique lifestyle.”
“Many human conditions, including diabetes, age-related diseases, neurodegeneration, and muscle atrophy, stem from issues with energy production and mitochondrial function,” notes Dr. Pedro Galante from Sirio Libanes Hospital.
“While further research is essential, sloth cell lines may serve as a valuable model for exploring how organisms adapt to low-energy conditions and the complications arising from diseases.”
“In the long run, this knowledge could enhance research in areas such as tissue preservation, emergency medicine, aging, metabolic disorders, and even long-duration space travel.”
This study was published in the journal BMC Biology.
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M. Uliano Silva et al. Increased retrocopy load and sloth-specific expansions reveal mammalian genome evolution. BMC Biol published online on May 19, 2026. doi: 10.1186/s12915-026-02632-5
Source: www.sci.news