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SUNDAY SCIENCE: ON THE TRAIL OF THE DENISOVANS  
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Carl Zimmer
March 2, 2024
New York Times
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_ DNA has shown that the extinct humans thrived around the world,
from chilly Siberia to high-altitude Tibet — perhaps even in the
Pacific islands. _

Researchers at Hebrew University reconstructed the face of a
Denisovan based on DNA alone. Almost no fossils of Denisovans have
been found., Maayan Harel/Hebrew University in Jerusalem, via
Associated Press

 

Neanderthals may have vanished 40,000 years ago, but they are no
strangers to us today. Their stocky skeletons dazzle in museums around
the world. Their imagined personas star in television ads
[[link removed]].
When Kevin Bacon
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Instagram that his morning habits are like those of a Neanderthal, he
did not stop to explain that our ancient cousins interbred with modern
humans expanding out of Africa.

But there’s no such familiarity with the Denisovans, a group of
humans that split from the Neanderthal line and survived for hundreds
of thousands of years before going extinct. That’s largely because
we have so few of their bones. In a new review paper,
anthropologists tally
[[link removed]] all of the
fossils that have been clearly identified as Denisovan since the first
discovery in 2010. The entire list
[[link removed]] consists
of half a broken jaw, a finger bone, a skull fragment, three loose
teeth and four other chips of bone.

“The bits of Denisovan we have, it’s almost nothing,” said Janet
Kelso, a paleoanthropologist at the Max Planck Institute for
Evolutionary Anthropology in Leipzig, Germany, who helped write the
review.

Nevertheless, many scientists are growing increasingly fascinated by
Denisovans. Like us, they were extraordinarily resilient, arguably
more so than Neanderthals. “I find Denisovans way more
interesting,” said Emilia Huerta-Sánchez, a geneticist at Brown
University.

What the Denisovans lack in fossils they make up for in DNA.
Geneticists have been able to extract bits of genetic material from
teeth and bones dating back 200,000 years. They have found genetic
clues in the dirt of cave floors. And billions of people on Earth
carry Denisovan DNA, inherited from interbreeding.

The evidence offers a picture of remarkable humans who were able to
thrive across thousands of miles and in diverse environments, from
chilly Siberia to high-altitude Tibet to woodlands in Laos — perhaps
even in the Pacific islands. Their versatility rivals our own.

“What we have found out about Denisovans is that, from a behavioral
perspective, they were much more like modern humans,” said Laura
Shackelford, a paleoanthropologist at the University of Illinois.

The Denisovans get their name from the Denisova Cave in Siberia, where
their remains were first identified. Russian paleontologists had been
pulling up bits of bone from the cave floor for years when Dr. Kelso
and other researchers offered to search them for DNA.

A molar tooth somewhere between 122,700 and 194,400 years old
contained Neanderthal-like genes. But the tooth’s DNA was distinct
enough to suggest it had come from a separate branch of human
evolution. A finger bone dating back 51,600 to 76,200 years belonged
to the same lineage, demonstrating that it had existed for tens of
thousands of years — if not more.

Since then, researchers have found more Denisovan fossils in the cave,
and they have also gathered loose genetic material from the cave
floor. The samples date from 200,000 to 50,000 years ago. A
90,000-year-old bone fragment belonged to a Denisovan-Neanderthal
hybrid
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showing that the two groups sometimes interbred.

Dr. Kelso and her colleagues quickly came to suspect that the
Denisovans had not been limited to Siberia. The researchers found that
some stretches of the ancient humans’ DNA closely matched genetic
material carried around by people in East Asia, Native Americans,
Aboriginal Australians and people in New Guinea and other islands in
the area.

When modern humans expanded out of Africa some 60,000 years ago, the
Denisovans must have been in their path in order to interbreed and
introduce some of their genes into our lineage. But it wasn’t until
2019 that scientists found the first fossil trace of Denisovans beyond
Siberia, in a high-altitude cave in Tibet
[[link removed]].

Researchers there found part of a jaw dating back more than 160,000
years with Denisovan-like teeth. It also contained proteins with a
molecular structure that might be expected from a Denisovan, based on
their genes. The following year, the researchers reported that the
cave floor contained Denisovan DNA
[[link removed]].

In 2022, Dr. Shackelford and her colleagues made a discovery
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could extend the Denisovan range to Southeast Asia, right in the path
of modern humans in their early waves out of Africa. In a cave in
Laos, they found a tooth about as old as the Denisovan jaw, and
matching the tooth embedded in it.

The Laotian tooth did not yield any DNA, however, so the researchers
have started sifting through sediments in nearby caves. “We have
loads of DNA,” Dr. Shackelford said. “But we don’t know yet what
all that DNA represents.”

Other researchers are surveying the Denisovan DNA inherited by living
people. The pattern of mutations documented so far suggests that
several genetically distinct groups of Denisovans interbred with our
ancestors. What’s more, none of those Denisovan groups was closely
related to the ones who occupied the Denisova cave.

Some of the most intriguing results have come from studies on people
in New Guinea and the Philippines. They show signs of repeated
instances of interbreeding with Denisovans that were distinct from
what occurred on mainland Asia. Dr. Kelso and other experts on
Denisovans suspect that when sea levels were low during the last ice
age, Denisovans may have walked to New Guinea and the Philippines,
where they lived for thousands of years before modern humans arrived.

Put together, these findings suggest that Denisovans thrived in vastly
different environments. They endured the harsh winters of Siberia and
the thin air of the Tibetan plateau. In Laos, Dr. Shackleford and her
colleagues have found that Denisovans lived in open woodlands with
herds of dwarf elephants and other mammals to hunt. And they may have
lived in rainforests in New Guinea and the Philippines.

That flexibility stands in sharp contrast to Neanderthals, who adapted
to the cold climate of Europe and western Asia but did not expand
elsewhere.

The Denisovans’ versatility may have helped them last for a long
time. People in New Guinea may have inherited some Denisovan DNA from
interbreeding just 25,000 years ago
[[link removed]].

Dr. Shackelford said findings like these raised the possibility that
Denisovans and modern humans coexisted and interacted for tens of
thousands of years — though whether they communicated is unclear.
“That’s really going down the rabbit hole,” Dr. Shackelford
said.

After the Denisovans disappeared, their genetic legacy lived on.
Certain genes of Denisovans have become more common because they
provide an evolutionary advantage in modern humans. In Tibet
[[link removed]], Dr.
Huerta-Sánchez and her colleagues have found a Denisovan gene that
helps people survive at high altitudes. She has also found
that Native Americans
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Denisovan gene for a mucus protein, though its benefit remains a
mystery.

In New Guinea
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Denisovan genes have been favored by people living in the lowlands,
while others are favored in the highlands. The lowland genes appear to
help fight infections. It’s possible that high rates of malaria and
other diseases make those genes valuable.

But in the highlands, the Denisovan genes with the evolutionary
advantage are active in the brain. Michael Dannemann, an evolutionary
geneticist at the University of Tartu in Estonia who led the New
Guinea study, speculated that at high altitudes in New Guinea, people
might face periods of food shortages. “You might have to adapt body
parts that use a lot of energy, and one that consumes a lot of energy
in humans is the brain,” he said.

Dr. Shackelford predicted that the search for more Denisovan fossils
would be hard, because the humid conditions in places like Laos
don’t favor the survival of skeletons. “I’m begging for
bones,” she said. “But I am going to be wanting bones for a long
time.”

_CARL ZIMMER [[link removed]] covers news
about science for The Times and writes the Origins column
[[link removed]]. I report on life — from
microbes at the bottom of the sea to high-flying migratory birds to
aliens that may dwell on other planets. For my column, I focus on how
life today got its start, including our own species. Along with
covering basic science, I write stories about how biological
discoveries evolve into medical applications, such as editing genes
and tending to our microbiome. _

_I wrote my first story for The Times in 2004. In 2013 I became a
columnist. I began my career in journalism at Discover Magazine, where
I rose to senior editor. I went on to write articles for magazines
including The Atlantic, Scientific American, Wired and Time._

_I also write books about science. So far, I’ve published 14,
including “She Has Her Mother’s Laugh,” “Life’s Edge,” and
“Parasite Rex.” I am professor adjunct at Yale’s Department of
Molecular Biophysics and Biochemistry, where I teach seminars on
writing and biology lecture courses. I have also co-authored a
textbook on evolutionary biology, now in its fourth edition._

_My books and articles have earned a number of awards including the
National Academics Communication Award and the Stephen Jay Gould
Prize, given out by the Society for the Study of Evolution. I have won
fellowships from the Johns Simon Guggenheim Foundation and the Alfred
P. Sloan Foundation. During the Covid-19 pandemic, I contributed to
the coverage that won The Times the Pulitzer Prize for Public Service
in 2021. I am, to my knowledge, the only writer after whom both a
species of tapeworm and an asteroid have been named._

_I live with my wife in Connecticut, alongside salt marshes rife with
snapping turtles._

_Subscribe to the NEW YORK TIMES.
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__

Quantum Physics Makes Small Leap with Microscopic Gravity Measurement
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Ian Sample
Science editor, The Guardian
Experiment records minuscule gravitational pull as a step to
understanding how gravity operates at subatomic level
February 23, 2024

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