Journal Critique Neanderthal vs Denisovan Essay

The journal article included in this assignment discusses the roots of human evolution with respect to two close relatives of present day Homo Sapiens.. Your assignment is to read the article and in a 1-2 page essay complete the questions associated with the article. Upload your complete answers to the  questions to CANVAS by Mar. 15. The answers should be detailed and comprehensive essay type answers, not just one sentence responses. Outside references may be used with appropriate APA formatting.

For reference:

Thesis statement: A thesis statement usually appears at the middle or end of the introductory paragraph of a paper, and it offers a concise summary of the main point or claim of the essay, research paper, or science article etc. It is usually expressed in one sentence, and the statement may be reiterated elsewhere.

NEWS: NATURE
22 August 2018
•
Correction 23 August 2018
Mum’s a Neanderthal, Dad’s a Denisovan: First
discovery of an ancient-human hybrid
Genetic analysis uncovers a direct descendant of two different groups of early humans.
Palaeogeneticists Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in
Leipzig, Germany,
Denny inherited one set of chromosomes from her Neanderthal ancestors, depicted in this model.Credit:
Christopher Rynn/University of Dundee
A female who died around 90,000 years ago was half Neanderthal and half Denisovan, according to genome
analysis of a bone discovered in a Siberian cave. This is the first time scientists have identified an ancient
individual whose parents belonged to distinct human groups. The findings were published on 22 August in
Nature1
“To find a first-generation person of mixed ancestry from these groups is absolutely extraordinary,” says
population geneticist Pontus Skoglund at the Francis Crick Institute in London. “It’s really great science
coupled with a little bit of luck.”
The team, led by palaeogeneticists Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany, conducted the genome analysis on a single bone fragment recovered from
Denisova Cave in the Altai Mountains of Russia. This cave lends its name to the ‘Denisovans’, a group of
extinct humans first identified on the basis of DNA sequences from the tip of a finger bone discovered2 there in
2008. The Altai region, and the cave specifically, were also home to Neanderthals.
Divided by DNA: The uneasy relationship between
archaeology and ancient genomics
Given the patterns of genetic variation in ancient and modern humans, scientists already knew that Denisovans
and Neanderthals must have bred with each other — and with Homo sapiens (See ‘Tangled Tree’). But no one
had previously found the first-generation offspring from such pairings, and Pääbo says that he questioned the
data when his colleagues first shared them. “I thought they must have screwed up something.” Before the
discovery of the Neanderthal–Denisovan individual, whom the team has affectionately named Denny, the best
evidence for so close an association was found in the DNA of a Homo sapiens specimen who had a Neanderthal
ancestor within the previous 4–6 generations3.
TANGLED TREE
A female born to a Neanderthal mother and Denisovan father roughly
90,000 years ago – nicknamed Denny – is one of many examples of
interbreeding between ancient human groups.
An unknown hominin species
interbred with Denisovans or
their ancestors.
The Altai Neanderthal’ s genome
revealed m ixture with an early
Homo sapiens lineage.
-90,000
years ago
>1 million
years ago
I
I
Mystery hominin species
Denny’s
father
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Neanderthals
I
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Altai Denny’s Vindija
Neanderthal mother. Neandert.hal
.
.
.
.
Early modernhuman lineage
Asians
Q
\ Interbreeding
\ episode or event
Europeans
Africans
◊
The ancestry of Denny’s mother was a
surprise. She was more closely related to
a 55,000-year-old Neanderthal from
Vindija cave in Croat ia than to an ‘Altai
Neanderthal’, who lived in Denisova Cave
roughly 30,000 years before Denny.
All non -Afric an
humans carry traces
of Neanderthal DNA,
owing to pairings
some 47,000 – 6 5,000
years ago.
@nature
Ancestry revealed
Pääbo’s team first uncovered Denny’s remains several years ago, by looking through a collection of more than
2,000 unidentified bone fragments for signs of human proteins. In a 2016 paper4, they used radiocarbon dating
to determine that the bone belonged to a hominin who lived more than 50,000 years ago (the upper limit of the
dating technique; subsequent genetic analysis has put the specimen at around 90,000 years old, according to
Pääbo). They then sequenced the specimen’s mitochondrial DNA — the DNA found inside cells’ energy
converters — and compared that data to sequences from other ancient humans. This analysis showed that the
specimen’s mitochondrial DNA came from a Neanderthal.
But this was only half of the picture. Mitochondrial DNA is inherited from the mother and represents just a
single line of inheritance, leaving the identity of the father and the individual’s broader ancestry unknown.
A bone fragment was sequenced for its genome.Credit: Thomas Higham/University of Oxford
In the latest study, the team sought to get a clearer understanding of the specimen’s ancestry by sequencing its
genome and comparing the variation in its DNA to that of three other hominins — a Neanderthal and a
Denisovan, both found in Denisova Cave, and a modern-day human from Africa. Around 40% of DNA
fragments from the specimen matched Neanderthal DNA — but another 40% matched the Denisovan. By
sequencing the sex chromosomes, the researchers also determined that the fragment came from a female, and
the thickness of the bone suggested she was at least 13 years old.
With equal amounts of Denisovan and Neanderthal DNA, the specimen seemed to have one parent from each
hominin group. But there was another possibility: Denny’s parents could have belonged to a population of
Denisovan–Neanderthal hybrids.
A fascinating genome
To work out which of these options was more likely, the researchers examined sites in the genome where
Neanderthal and Denisovan genetics differ. At each of these locations, they compared fragments of Denny’s
DNA to the genomes of the two ancient hominins. In more than 40% of cases, one of the DNA fragments
matched the Neanderthal genome, whereas the other matched that of a Denisovan, suggesting that she had
acquired one set of chromosomes from a Neanderthal and the other from a Denisovan. That made it clear that
Denny was the direct offspring of two distinct humans, says Pääbo. “We’d almost caught these people in the
act.”
Evidence mounts for interbreeding bonanza in
ancient human species
The results convincingly demonstrate that the specimen is indeed a first-generation hybrid, says Kelley Harris, a
population geneticist at the University of Washington in Seattle who has studied hybridization between early
humans and Neanderthals. Skoglund agrees: “It’s a really clear-cut case,” he says. “I think it’s going to go into
the textbooks right away.”
Harris says that sexual encounters between Neanderthals and Denisovans might have been quite common. “The
number of pure Denisovan bones that have been found I can count on one hand,” she says — so the fact that a
hybrid has already been discovered suggests that such offspring could have been widespread. This raises
another interesting question: if Neanderthals and Denisovans mated frequently, why did the two hominin
populations remain genetically distinct for several hundred-thousand years? Harris suggests that Neanderthal–
Denisovan offspring could have been infertile or otherwise biologically unfit, preventing the two species from
merging.
Neanderthal-Denisovan pairings could also have had some advantages, even if there were other costs, says
Chris Stringer, a palaeoanthropologist at the Natural History Museum in London. Neanderthals and Denisovans
were less genetically diverse than modern humans, and so interbreeding might have provided a way of “topping
up” their genomes with a bit of extra genetic variation, he says. The study also raises questions over how
matings between different human groups happened, says Stringer — for example, whether or not they were
consensual. A more detailed account of the gene flow between Neanderthals and Denisovans in the future might
offer hints into ancient human behaviour.
Missed connections
Pääbo agrees that Neanderthals and Denisovans would have readily bred with each other when they met – but he
thinks that those encounters were rare. Most Neanderthal remains have been found across western Eurasia,
whereas Denisovans have so far been discovered only in their eponymous Siberian cave. Although the two
groups’ home turf overlapped in the Altai Mountains and possibly elsewhere, these areas would have been
sparsely populated. “I think any Neanderthal that lived west of the Urals would never ever meet a Denisovan in
their life,” Pääbo says, referring to the mountain range that slices through western Russia and Kazakhstan.
Denny’s remains were discovered in Denisova Cave in southern Siberia.Credit: Bence Viola/Max Planck
Institute for Evolutionary Anthropology
But sometimes, Neanderthal populations might have travelled from western Eurasia to Siberia, or vice-versa.
On the basis of the variation in the specimen’s genome, the team deduced that Denny’s Neanderthal mother was
more closely related to a Neanderthal specimen found thousands of kilometres away, in Croatia, than to another
found less than 1 metre away in the same cave.
Neanderthals built cave structures — and no one
knows why
The Croatian Neanderthal died died much more recently than Denny — about 55,000 years ago — while the
Neanderthal from Denisova Cave is around 120,000 years old. That leaves two possibilities to explain the
ancestry of Denny’s mother: either a population of European Neanderthals came east to the Altai Mountains and
partly replaced the region’s Neanderthals before the hybrid was born, or a group of Neanderthals could have left
the Altai Mountains for Europe sometime after Denny’s birth. Either way, says Harris, Neanderthals “didn’t just
stay in one place for thousands of years”.
With a Neanderthal mother and a Denisovan father, what should we call the new specimen? “We shy away a
little from the word ‘hybrid’,” says Pääbo. The term implies that the two groups are discrete species of human,
whereas in reality the boundaries between them are blurry — as the new study shows. Defining a species in the
natural world is not always clear-cut, says Harris, and it’s interesting to see long-running debates about how to
categorize organisms start to be applied to humans.
Whatever scientists decide to call Denny, Skoglund says he would have loved to be able to meet her. “It’s
probably the most fascinating person who’s ever had their genome sequenced.”
Nature 560, 417-418 (2018)
doi: 10.1038/d41586-018-06004-0
Updates & Corrections
•
Correction 23 August 2018: This story has been corrected to indicate that European Neanderthals
would have travelled east to reach the Altai Mountains, not west.
Science Article Review Questions
“Neanderthal mother, Denisovan father!
Hybrid fossil”
Please complete the following questions with essay type responses. If outside
resources are used please properly format those sources using APA
formatting.
1. Who were Neanderthals, a) what time period did they live in, b) where were they
geographically found on Earth and, c) what is their importance in Human evolution?
2. Who were Denisovans, a) what time period did they live in, b) where were they
geographically found on Earth and, c) what is their importance in Human evolution?
3.
What does the phrase “sequenced the genome” mean?
4.
What is the importance of the bone fragment that is illustrated in the article?
5.
What is the thesis of the article?
6.
Who are the authors of the article?
7.
Where did the information for the article come from and is it a reliable resource?