In conjunction with armadillos and anteaters, sloths constitute a segment of Xenarthra, the sole infraclass of placental mammals to emerge from South America. Recent investigations have involved the sequencing and examination of chromosome-level genomic data from both the Linnaeus’s two-toed sloth (Choloepus didactylus) and the southern anteater (Tamandua tetradactyla). These analyses have revealed distinctive genetic elements associated with energy generation within sloths, thereby providing potential insights into the evolutionary trajectory that led to their exceptionally sluggish metabolic rates among mammals.
The Linnaeus’s two-toed sloth (Choloepus didactylus) at London Zoo. Image credit: Dick Culbert / CC BY 2.0.
The Xenarthran lineage has persisted for an impressive 65.5 million years, with ancient sloth relatives including terrestrial giants of elephantine proportions.
Currently, extant sloths are exclusively arboreal and are categorized into two principal divisions: the two-toed and the three-toed sloths.
These creatures dedicate the majority of their existence within the arboreal canopy, where they remain largely immobile and effectively camouflaged. Their transitions between branches, undertaken for the consumption of foliage and fruits, occur with a decidedly unhurried tempo.
They exhibit the lowest metabolic rates encountered in the mammalian class, frequently registering at less than half the anticipated level for their respective body masses.
As a mechanism for energy conservation, they possess the capacity to modulate their internal body temperature, shifting between self-regulation and passive adaptation to ambient environmental conditions.
Despite their leisurely pace of movement, they are proficient swimmers, capable of traversing considerable aquatic distances when in search of reproductive partners.
In pursuit of a more profound comprehension of the unique physiological characteristics of sloths, a team led by Marcela Uliano-Silva, a researcher at the Wellcome Sanger Institute, embarked on a genomic expedition.
“Nature has already conducted myriad experimental trials,” remarked Dr. Uliano-Silva.
“By scrutinizing extraordinary fauna such as sloths, we occasionally unearth biological solutions that have not manifested in human evolution.”
“Employing genomic techniques to reconstruct past evolutionary events, we have identified ‘jumping genes’ that have been preserved by sloths across eons.”
“These gene sequences, peculiar to sloths, are intricately linked with mitochondria and metabolic pathways, suggesting a potential connection to the evolutionary development of their remarkably decelerated metabolism.”
The research undertaking involved the meticulous sequencing and analysis of the genetic blueprint of both the Linnaeus’s two-toed sloth and the southern anteater.
It was discovered that the sloth genome harbored multiple active copies of transposable genetic elements, colloquially termed ‘transposons’ or ‘jumping genes.’ These are segments of DNA with the ability to replicate and reposition themselves throughout the genome.
Through the application of genomic analysis to trace the evolutionary lineage of sloths backward in time, it was determined that these ‘jumping genes’ originated in the ancient common ancestor of all extant sloth species approximately 30 million years ago.
These genetic constituents have subsequently been maintained through the ages, becoming an intrinsic and distinguishing component of the sloth genome.
The research team expressed surprise at the discovery that a significant proportion of these genes are associated with mitochondria—the cellular organelles responsible for energy production—and with metabolic processes.
Given that sloths possess one of the most distinctive metabolic profiles among mammals, it is posited that these sloth-specific genes play a role in their remarkable environmental adaptations and the evolutionary trajectory of their profoundly slow metabolic rate.
“Sloths exhibit the slowest metabolism of any mammalian species, yet they maintain robust health,” stated Dr. Camila Mazzoni, a researcher affiliated with the Leibniz Institute for Zoo and Wildlife Research and the Berlin Center for Genomics in Biodiversity Research.
“Elucidating the mechanisms by which they achieve this could yield novel insights into the sophisticated management of cellular energy.”
“Our findings suggest a potential for sloths to have developed genetic ‘contingency plans’ that assist in compensating for their ‘attenuated mitochondria’ and support their singular mode of existence.”
“Numerous human ailments, encompassing conditions such as diabetes, age-related degenerative disorders, neurodegeneration, and muscular atrophy, are intrinsically linked to dysfunctions in energy production and mitochondrial activity,” observed Dr. Pedro Galante, a researcher at the Hospital Sírio Libanês.
“While further investigation is imperative, sloth cellular models may offer a natural paradigm for understanding how organisms navigate states of diminished energy and the pathological consequences of compromised cellular function.”
“In the broader context, this research holds the potential to inform advancements in fields such as tissue preservation, critical care medicine, gerontology, metabolic disorders, and even extended interplanetary voyages.”
This particular research contribution has been formally published in the esteemed journal BMC Biology.
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M. Uliano-Silva et al. Elevated retrocopy burden and sloth-specific expansions illuminate mammalian genome evolution. BMC Biol, published online May 19, 2026; doi: 10.1186/s12915-026-02632-5
