[Genomics analysis indicates that at least 800,000 years ago
breeding individuals sank to as few as 1,300]
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SUNDAY SCIENCE: POPULATION COLLAPSE ALMOST WIPED OUT HUMAN ANCESTORS
 
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Hannah Devlin
August 31, 2023
The Guardian
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_ Genomics analysis indicates that at least 800,000 years ago
breeding individuals sank to as few as 1,300 _

The skull of Homo heidelbergensis. Scientists speculate that the
species could have arisen owing to the tiny population of human
ancestor species., Sabena Jane Blackbird/Alamy

 

Early human ancestors came close to eradication in a severe
evolutionary bottleneck between 800,000 and 900,000 years ago,
according to scientists.

A genomics analysis of more than 3,000 living people suggested that
our ancestors’ total population plummeted to about 1,280 breeding
individuals for about 117,000 years. Scientists believe that an
extreme climate event could have led to the bottleneck that came close
to wiping out our ancestral line.

“The numbers that emerge from our study correspond to those of
species that are currently at risk of extinction,” said Prof Giorgio
Manzi, an anthropologist at Sapienza University of Rome and a senior
author of the research.

However, Manzi and his colleagues believe that the existential
pressures of the bottleneck could have triggered the emergence of a
new species, _Homo heidelbergensis_, which some believe is the shared
ancestor of modern humans and our cousins, the Neanderthals and
Denisovans. _Homo sapiens_ are thought to have emerged about 300,000
years ago.

“It was lucky [that we survived], but … we know from evolutionary
biology that the emergence of a new species can happen in small,
isolated populations,” said Manzi.

Prof Chris Stringer, the head of human origins at the Natural History
Museum in London, who was not involved in the research, said:
“It’s an extraordinary length of time. It’s remarkable that we
did get through at all. For a population of that size, you just need
one bad climate event, an epidemic, a volcanic eruption and you’re
gone.”

The decline appears to coincide with significant changes in global
climate that turned glaciations into long-term events, a decrease in
sea surface temperatures, and a possible long period of drought in
Africa and Eurasia. The team behind the work said the time window also
coincides with a relatively empty period on the fossil record.

“We know that between about 900,000 and 600,000 years ago, the
fossil record in Africa is very scarce, if not almost absent, while
both before and after we have a greater number of fossil evidence,”
said Manzi. “The same can be said for Eurasia: for example, in
Europe we have a species known as _Homo antecessor_ around 800,000
years ago and then nothing for about 200,000 years.”

However, Stringer said there was not convincing evidence for a global
“blank” in the fossil record of early humans, raising the
possibility that whatever caused the bottleneck was a more local
phenomenon. “Maybe this bottleneck population was stuck in some area
of Africa surrounded by desert,” he said.

The paper, published in the journal Science
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genomic sequences from 3,154 people alive today, from 10 African and
40 non-African populations. By looking at the different versions of
genes across a population, it is possible to roughly date when
specific genes first emerged – the more time that has elapsed, the
more chance for different variants of a gene to crop up. By estimating
the frequency with which genes have emerged over time, scientists can
gain insights into how ancestral populations grew and shrank over
time.

The analysis found evidence for the bottleneck in all the African
populations, but only a weak signal of the event was detected in the
40 non-African populations. This is probably due to the ancestors of
those of non-African heritage having in effect undergone a more recent
population bottleneck during the out-of-Africa migration, which would
be expected to mask the earlier event.

The timing roughly coincides with when the last shared ancestor with
Neanderthals and another ancient human species, the Denisovans, are
believed to have roamed the Earth. Scientists now want to look at
whether genetic samples from these ancient cousins share evidence of
the same bottleneck, which could give new insights into when, where
and why the species diverged.

_HANNAH DEVLIN is the Guardian's science correspondent, having
previously been science editor of the Times. She has a PhD in
biomedical imaging from the University of Oxford. Hannah also presents
the Science Weekly podcast
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THE TRANSFORMATIVE, ALARMING POWER OF GENE EDITING
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A rogue scientist showed that CRISPR gives humans the ability to
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By DANA GOODYEAR
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* Science
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* Evolution
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* ancient humans
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* Africa
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* Climate Change
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