The recent discovery of Denisovans, a previously unknown hominin lineage, has significantly revolutionized our understanding of human evolutionary pathways over the past ten years. In stark contrast to the more abundant Neanderthal fossil evidence, the archaeological record for Denisovans is remarkably sparse, comprising merely a handful of skeletal fragments. Current scientific investigations propose that multiple Denisovan populations, which presumably occupied a vast territorial expanse, were specialized for diverse ecological settings and contributed genetic material to early human populations through numerous, discrete interbreeding occurrences that played a role in shaping contemporary human ancestry.
A portrait of a juvenile female Denisovan based on a skeletal profile reconstructed from ancient DNA methylation maps. Image credit: Maayan Harel.
The initial identification of Denisovans, an extinct group of hominins, originated from the genetic sequencing of a bone fragment discovered within Denisova Cave, situated in the Altai Mountains of southern Siberia.
“This represented a truly groundbreaking revelation pertaining to human evolution within the last decade,” stated Dr. Linda Ongaro, a research fellow associated with Trinity College Dublin.
Subsequent genomic analyses have indicated that Denisovans diverged from Neanderthals approximately 400,000 years ago, and that at least two distinct Denisovan groups interbred with the ancestral populations of contemporary Asian peoples.
To date, the sole physical remnants attributed to Denisovans consist of a partial finger bone, three molars, and a fragment of a skull from Denisova Cave, alongside a mandible and a rib bone recovered from Baishiya Karst Cave, located on the northeastern periphery of the Tibetan Plateau.
“It is a prevalent misunderstanding to assume human evolution progressed in a linear and unblemished fashion from a singular progenitor; however, with each new discovery, we increasingly acknowledge the prevalence of interspecies gene flow with various hominin groups, which contributed to our current biological makeup,” commented Dr. Ongaro.
“In contrast to the skeletal evidence for Neanderthals, the fossil inventory for Denisovans is limited to that very finger bone, a jawbone, teeth, and fragments of a skull.”
“Nevertheless, by meticulously examining the residual Denisovan gene segments present in the genomes of modern humans, researchers have unearthed evidence pointing to a minimum of three historical instances where genetic material from distinct Denisovan populations was incorporated into the genetic profiles of contemporary humans.”
Each of these genetic contributions exhibits varying degrees of relatedness to the sequenced Denisovan individual from Altai, suggesting a complex genealogical connection among these related evolutionary branches.
In their recent publication, Dr. Ongaro and her collaborator, Professor Emilia Huerta-Sanchez of Trinity College Dublin and Brown University, presented findings that suggest several Denisovan populations, believed to have inhabited an extensive geographic territory spanning from Siberia to Southeast Asia, and from Oceania to South America, were biologically adapted to a variety of differing environments.
Furthermore, they detailed the identification of numerous genes of Denisovan origin that conferred survival advantages to modern humans within their respective ecological niches.
“Among these is a specific genetic region that bestows tolerance to hypoxia, or reduced oxygen levels, a trait that is remarkably consistent with its prevalence in Tibetan populations; augmented immunological responses are conferred by multiple genes; and another gene influences lipid metabolism, generating heat when exposed to cold, thus providing an adaptive advantage to Inuit communities inhabiting the Arctic,” explained Dr. Ongaro.
“There are manifold avenues for future research that will facilitate a more comprehensive narrative of the impact Denisovans had on modern human populations. These include conducting more in-depth genetic analyses within under-researched demographic groups, which could potentially unveil currently undetected traces of Denisovan heritage.”
“Moreover, the integration of additional genetic data with archaeological findings — should more Denisovan fossils be unearthed — would undoubtedly serve to fill in several significant gaps in our knowledge.”
This scholarly article was published in the esteemed journal Nature Genetics and can be accessed via this link: paper.
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L. Ongaro & E. Huerta-Sanchez. A history of multiple Denisovan introgression events in modern humans. Nat Genet, published November 5, 2024; doi: 10.1038/s41588-024-01960-y
