[[link removed]]

PRINCETON STUDY MAPS 200,000 YEARS OF HUMAN–NEANDERTHAL
INTERBREEDING  
[[link removed]]


 

Princeton University
July 13, 2025
Science Daily
[[link removed]]

*
[[link removed]]
*
[[link removed]]
*
*
[[link removed]]

_ For centuries, we’ve imagined Neanderthals as distant cousins.
But modern humans and Neanderthals didn’t just cross paths; they
repeatedly interbred, shared genes, and even merged populations over
nearly 250,000 years. _

Princeton University’s Josh Akey and Southeast University’s
Liming Li identified a first wave of contact about 200-250,000 years
ago, another wave 100-120,000 years ago, and the largest one about
50-60,000 years ago, Credit: Matilda Luk, Princeton University

 

SUMMARY: For centuries, we’ve imagined Neanderthals as distant
cousins — a separate species that vanished long ago. But thanks to
AI-powered genetic research, scientists have revealed a far more
entangled history. Modern humans and Neanderthals didn’t just cross
paths; they repeatedly interbred, shared genes, and even merged
populations over nearly 250,000 years. These revelations suggest that
Neanderthals never truly disappeared — they were absorbed. Their
legacy lives on in our DNA, reshaping our understanding of what it
means to be human.

When the first Neanderthal bones were uncovered in 1856, they sparked
a flood of questions about these mysterious ancient humans. Were they
similar to us or fundamentally different? Did our ancestors cooperate
with them, clash with them, or even form relationships? The discovery
of the Denisovans, a group closely related to Neanderthals that once
lived across parts of Asia and South Asia, added even more intrigue to
the story.

Now, a group of researchers made up of geneticists and artificial
intelligence specialists is uncovering new layers of that shared
history. Led by Joshua Akey, a professor at Princeton’s Lewis-Sigler
Institute for Integrative Genomics, the team has found strong evidence
of genetic exchange between early human groups, pointing to a much
deeper and more complex relationship than previously understood.

"This is the first time that geneticists have identified multiple
waves of modern human-Neanderthal admixture," said Liming Li, a
professor in the Department of Medical Genetics and Developmental
Biology at Southeast University in Nanjing, China, who performed this
work as an associate research scholar in Akey's lab.

"We now know that for the vast majority of human history, we've had a
history of contact between modern humans and Neanderthals," said Akey.
The hominins who are our most direct ancestors split from the
Neanderthal family tree about 600,000 years ago, then evolved our
modern physical characteristics about 250,000 years ago.

"From then until the Neanderthals disappeared -- that is, for about
200,000 years -- modern humans have been interacting with Neanderthal
populations," he said.

The results of their work were published the journal _Science_.

RETHINKING THE ICE AGE STEREOTYPE

Neanderthals, once stereotyped as slow-moving and dim-witted, are now
seen as skilled hunters and tool makers who treated each other's
injuries with sophisticated techniques and were well adapted to thrive
in the cold European weather.

(Note: All of these hominin groups are humans, but to avoid saying
"Neanderthal humans," "Denisovan humans," and
"ancient-versions-of-our-own-kind-of-humans," most archaeologists and
anthropologists use the shorthand Neanderthals, Denisovans, and modern
humans.)

Using genomes from 2,000 living humans as well as three Neanderthals
and one Denisovan, Akey and his team mapped the gene flow between the
hominin groups over the past quarter-million years.

The researchers used a genetic tool they designed a few years ago
called IBDmix, which uses machine learning techniques to decode the
genome. Previous researchers depended on comparing human genomes
against a "reference population" of modern humans believed to have
little or no Neanderthal or Denisovan DNA.

Akey's team has established that even those referenced groups, who
live thousands of miles south of the Neanderthal caves, have trace
amounts of Neanderthal DNA, probably carried south by voyagers (or
their descendants).

With IBDmix, Akey's team identified a first wave of contact about
200-250,000 years ago, another wave 100-120,000 years ago, and the
largest one about 50-60,000 years ago.

CHALLENGING THE OUT-OF-AFRICA MODEL

That contrasts sharply with previous genetic data. "To date, most
genetic data suggests that modern humans evolved in Africa 250,000
years ago, stayed put for the next 200,000 years, and _then_ decided
to disperse out of Africa 50,000 years ago and go on to people the
rest of the world," said Akey.

"Our models show that there wasn't a long period of stasis, but that
shortly after modern humans arose, we've been migrating out of Africa
and coming back to Africa, too," he said. "To me, this story is about
dispersal, that modern humans have been moving around and encountering
Neanderthals and Denisovans much more than we previously recognized."

That vision of humanity on the move coincides with the archaeological
and paleoanthropological research suggesting cultural and tool
exchange between the hominin groups.

Li and Akey's key insight was to look for modern-human DNA in the
genomes of the Neanderthals, instead of the other way around. "The
vast majority of genetic work over the last decade has really focused
on how mating with Neanderthals impacted modern human phenotypes and
our evolutionary history -- but these questions are relevant and
interesting in the reverse case, too," said Akey.

They realized that the offspring of those first waves of
Neanderthal-modern matings must have stayed with the Neanderthals,
therefore leaving no record in living humans. "Because we can now
incorporate the Neanderthal component into our genetic studies, we are
seeing these earlier dispersals in ways that we weren't able to
before," Akey said.

SHRINKING POPULATIONS AND GENETIC ILLUSIONS

The final piece of the puzzle was discovering that Neanderthals had a
smaller population than researchers previously thought.

Scientists often estimate population size by looking at genetic
diversity. In general, more variation in the genome suggests a larger
group. But when Akey’s team applied their tool, IBDmix, they found
that much of the apparent diversity in Neanderthal DNA actually came
from genes inherited from modern humans, who had far larger
populations.

With this new insight, scientists lowered their estimate of the
Neanderthal breeding population from about 3,400 individuals to
roughly 2,400.

Taken together, these findings help explain how Neanderthals
disappeared from the fossil and genetic record around 30,000 years
ago.
 

"I don't like to say 'extinction,' because I think Neanderthals were
largely absorbed," said Akey. His idea is that Neanderthal populations
slowly shrank until the last survivors were folded into modern human
communities.

This "assimilation model" was first articulated by Fred Smith, an
anthropology professor at Illinois State University, in 1989. "Our
results provide strong genetic data consistent with Fred's hypothesis,
and I think that's really interesting," said Akey.

"Neanderthals were teetering on the edge of extinction, probably for a
very long time," he said. "If you reduce their numbers by 10 or 20%,
which our estimates do, that's a substantial reduction to an already
at-risk population.

"Modern humans were essentially like waves crashing on a beach, slowly
but steadily eroding the beach away. Eventually we just
demographically overwhelmed Neanderthals and incorporated them into
modern human populations."

_This research was supported by the National Institutes of Health
(grant R01GM110068 to JMA)._

JOURNAL REFERENCE: Liming Li, Troy J. Comi, Rob F. Bierman, Joshua M.
Akey. RECURRENT GENE FLOW BETWEEN NEANDERTHALS AND MODERN HUMANS OVER
THE PAST YEARS. _Science_, 2024; 385 (6705)
DOI: 10.1126/science.adi1768
[[link removed]]

* human evolution
[[link removed]]
* Homo sapiens
[[link removed]]
* Neanderthals
[[link removed]]
* Evolution
[[link removed]]

*
[[link removed]]
*
[[link removed]]
*
*
[[link removed]]

 

 

 

INTERPRET THE WORLD AND CHANGE IT

 

 

Submit via web
[[link removed]]

Submit via email
Frequently asked questions
[[link removed]]
Manage subscription
[[link removed]]
Visit xxxxxx.org
[[link removed]]

Twitter [[link removed]]

Facebook [[link removed]]

 




[link removed]

To unsubscribe, click the following link:
[link removed]