Denny (hybrid hominin)

Denny (Denisova 11)

Catalog no.	DC1227; GenBank Accession = KU131206
Common name	Denny (Denisova 11)
Species	1st generation Neanderthal/Denisovan hybrid
Age	90,000 years
Place discovered	Denisova Cave in the Altai Mountains, Siberia, Russia
Date discovered	2012
Discovered by	Viviane Slon, Svante Pääbo, Samantha Brown, Tom Higham, Michael Buckley, Katerina Douka et al.

Denny (Denisova 11) is an ~90,000 year old fossil specimen belonging to a ~13-year-old

Genomic sequencing and analysis led by paleo-geneticists Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology revealed that Denny was the offspring of a Neanderthal mother and a Denisovan father.^[1][3] Additionally, her genome suggests that her father also carried a small degree of Neanderthal ancestry from 300 to 600 generations prior to his lifetime.^[3]

These surprising genomic data has caused some paleontologists to speculate that interspecies mating between Denisovans and Neanderthals could have occurred with some frequency during several periods of contact over many thousands of years.^[3] Additionally, these findings lend support to the hypothesis that similar patterns of admixture, or interbreeding between archaic and modern humans, may have resulted in the partial absorption of Denisovans and Neanderthals into modern human populations.^[3]

Overview

Dating analyses in 2016 determined that Denny (Denisova 11) died about 90,000 years ago, and the bone's cortical thickness indicates an age at death of at least 13 years.^[3] An analysis of the whole genome sequence (total mitochondrial and nuclear DNA) indicates she was female, with a Neanderthal mother and a Denisovan father.^[1][2][3] While previous analyses of other ancient genomes concluded that Denisovans, Neanderthals, and modern humans interbred during the ice age in Europe and Asia, this find is the most direct evidence yet that various ancient hominins mated with each other and had offspring.^[2][5][6]

Previous analyses from other fossils found in this Siberian cave have shown that modern humans, Neanderthals, and Denisovans inhabited this site at various times, and that all three human species interbred with each other.^[2][6] The genes of both archaic human species are present in many people today, which suggests that when these groups met, gene flow occurred.^[2][5] It is not evident if the mating was consensual or if Denny was fertile.^[1] The discovery of Denisova 11 may support the notion that Neanderthals and Denisovans may not have undergone direct extinction but were partly assimilated into modern human populations.^[4][6]

Discovery

Denisova Cave

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Location of Denisova Cave in the Altai Mountains of Siberia

The finding consists of a single bone fragment about 2 cm long that was unearthed in 2012 by Russian archeologists at the Denisova Cave from layer 12 of the East Gallery.^[7] The cave is located in Denisova valley, Altai Mountains in Siberia, Russia.^[2][6] At the time, the origin of the bone fragment remained unknown because it was archived along with thousands of other nondescript bone fragments from the cave.^[4]

In 2015, Tom Higham and Katerina Douka, as part of Higham's "PalaeoChron Archived 18 August 2014 at the Wayback Machine" ERC project, decided to try and apply new scientific methods to see whether they could be used to find human remains amongst the thousands of unidentified bone samples in the site. With the collaboration of the head excavators of the Denisova site; Michael Shunkov and Anatoly Derevianko, they took several bags containing thousands of unidentified bone fragments back to the University of Oxford. Samantha Brown, an MSc student at the University of Oxford, worked on the project as part of her dissertation research, screening more than 2000 bone fragments.^[4] Using Zooarchaeology by Mass Spectrometry (ZooMS) and working with the laboratory of Michael Buckley at the University of Manchester, they were able to compare the collagen protein fingerprints derived from the Denisova Cave bones to animals and humans of known origin, and they discovered that one of these bones (DC1227) belonged to an archaic human.^[4][8][9] A micro-computed tomography (Micro CT) scan of the bone done by Fiona Brock at Cranfield University helped to reveal that the specimen had acid etching and pitting on its surface indicating it may have passed through the digestion system of an animal, likely a hyena.^[4] Direct radiocarbon dating estimated the specimen to be more than 50,000 years old, and the sequencing of its mitochondrial DNA (mtDNA) at the Max Planck Institute for Evolutionary Anthropology, showed that Denisova 11 had a sequence consistent with a Neanderthal origin.^[4]

Further work by scientists at the

The story is told in Tom Higham's book "The World Before Us: How science is revealing a new story of our human origins"^[11]

DNA analysis

The bone fragment, identified by the code DC1227 (GenBank Accession = KU131206) or as Denisova 11, may have originated from a human arm or leg.

Subsequent analyses showed a high likelihood that her Denisovan father also had some Neanderthal ancestry introduced into his genome hundreds of generations before his lifetime.[2]^[3] Denisova 11's genome thus constitutes the first direct evidence for at least two instances of interbreeding between Neanderthals and Denisovans.^[3][12] Even more surprising, the researchers determined that the girl's mother's genome was more closely related to Western European Neanderthal DNA, excavated thousands of miles away at the Vindija Cave, Croatia, than the Neanderthals who lived in the Siberian cave where her daughter's remains were found.^[2][3][8] This finding suggests that Neanderthals migrated in multiple waves from Western Europe to Central Eurasia and encountered the Denisovans several times over a span of tens of thousands of years, and possibly coexisted with them for periods of time.^[2][8][10]

Context and implications

Since the discovery of Neanderthal remains in the 19th century, many scientists have supported the hypothesis of interbreeding between archaic and modern humans, also known as hybridization, admixture, or hybrid-origin theory.

The discovery of Denny and other paleogenetic data acquired since 2010 show that human evolution should not be conceptualized as a simple linear or branched progression, but rather, as a complex interaction between related species over various periods of geographical isolation and convergence.[15]^[16][17][18] Ackermann, Mackay, and Arnold confirm, "Recent genomic research has shown that hybridization between substantially diverged lineages is the rule, not the exception, in human evolution."^[19] Acknowledging that there is still debate over how hybridization shaped human genotypes and phenotypes, the evolutionary biologists assert that hybridization was an essential creative force in the emergence of modern humans.^[19]

In January 2019, scientists published a chronology for the Pleistocene deposits in the Denisova Cave concluding that at least two groups of humans, including Denisovans, Neanderthals, and related hybrids, occupied the Siberian site from around 300,000 to 20,000 years ago, but more material evidence is needed to prove whether they ever coexisted there.^[20][21] Material data collected at the site, including stone tools, bracelets, and other ornaments suggest that Denisovans may have been capable of higher order thought akin to modern humans.^[21]

In February 2019, scientists discovered evidence, based on

References