human population bottleneck

[erik simpson]

https://www.science.org/doi/10.1126/science.abq7487

Genomic inference of a severe human bottleneck during the Early to
Middle Pleistocene transition

Abstract
Population size history is essential for studying human evolution.
However, ancient population size history during the Pleistocene is
notoriously difficult to unravel. In this study, we developed a fast
infinitesimal time coalescent process (FitCoal) to circumvent this
difficulty and calculated the composite likelihood for present-day human
genomic sequences of 3154 individuals. Results showed that human
ancestors went through a severe population bottleneck with about 1280
breeding individuals between around 930,000 and 813,000 years ago. The
bottleneck lasted for about 117,000 years and brought human ancestors
close to extinction. This bottleneck is congruent with a substantial
chronological gap in the available African and Eurasian fossil record.
Our results provide new insights into our ancestry and suggest a
coincident speciation event.

We had a narrow escape from extinction. When I read the news, sometimes
I think it's too bad we made it.

[JTEM]

Post by erik simpson
https://www.science.org/doi/10.1126/science.abq7487
Genomic inference of a severe human bottleneck during the Early to
Middle Pleistocene transition
Abstract
Population size history is essential for studying human evolution.
However, ancient population size history during the Pleistocene is
notoriously difficult to unravel. In this study, we developed a fast
infinitesimal time coalescent process (FitCoal) to circumvent this
difficulty and calculated the composite likelihood for present-day human
genomic sequences of 3154 individuals. Results showed that human
ancestors went through a severe population bottleneck with about 1280
breeding individuals between around 930,000 and 813,000 years ago.

It was 800,000 years ago, or a tad more recent.

"Molecular clock" or "Molecular dating" sucks. It always exaggerates.
It assumes a slow, clock like pace of change when, by definition, a
bottleneck event is pretty damn quick.

Google: Founder effect.

Within a single generation the genetics that typify a population can
completely change.

The premise is also based on a fantasy, not how DNA actually works. If
you do the Google, for instance, most sources insist that your DNA
will be completely wiped from humanity within a thousand years, barring
anything special. And of course if there is anything special then that
means any 10 other people's DNA will be wiped in a thousand years...

This is assuming that you all have living descendants.

Yes you have many, Many, MANY ancestors for whom not a trace of their
DNA can be found in you...

A fantastic illustration of this point is the LM3 or Chromosome 11
insert that identifies a mtDNA ancestor *Far* older than any
"Mitochondrial Eve" for billions of people, that would be completely
unknown and unguessed at without the lucky Chromosome 11 insert...

That's it. We leap from no-reason-to-so-much-as-suspect these deeply
archaic Eurasian ancestors to confirmation of their existence, all
because of one lucky mutation. And, it's a mutation that completely
dissolves the "Molecular Clock" mtDNA dating, as that mtDNA that
made the leap is strangely missing all this clock-like mutation...

[RonO]

Post by erik simpson
https://www.science.org/doi/10.1126/science.abq7487
Genomic inference of a severe human bottleneck during the Early to
Middle Pleistocene transition
Abstract
Population size history is essential for studying human evolution.
However, ancient population size history during the Pleistocene is
notoriously difficult to unravel. In this study, we developed a fast
infinitesimal time coalescent process (FitCoal) to circumvent this
difficulty and calculated the composite likelihood for present-day human
genomic sequences of 3154 individuals. Results showed that human
ancestors went through a severe population bottleneck with about 1280
breeding individuals between around 930,000 and 813,000 years ago. The
bottleneck lasted for about 117,000 years and brought human ancestors
close to extinction. This bottleneck is congruent with a substantial
chronological gap in the available African and Eurasian fossil record.
Our results provide new insights into our ancestry and suggest a
coincident speciation event.
We had a narrow escape from extinction.  When I read the news, sometimes
I think it's too bad we made it.

The estimate for when this bottleneck occurred has been going back
further in time for decades. The initial estimates at the turn of the
century that I recall were less than 100,000 years ago, but those
estimates were biased by the fact that nearly all DNA sequence came from
individuals of non African ancestry, so they were getting an estimate of
the subpopulation that made it out of Africa.

The estimate of around 1,000 individuals has been around for a long
time, but it sounds like the loss of ancestors occurred over a fairly
long time period due to reduced population size and likely truncation of
existing families. There were more than 1,000 individuals breeding
during the low population levels, but a lot of lineages went extinct
during that 117,000 year period. It could even be a speciation event
where a subpopulation took over. The chromosome fusion creating human
chromosome 2 has been estimated to have occurred 900,000 years ago.
Such fusions (if they are associated with reduction in viable gametes)
can be fixed in a small population. As this small population expanded
in size it could interbreed with individuals that did not have the
fusion, but gene flow would be reduced (hybrids would produce fewer
viable gametes). So even as the fusion containing population expanded,
they would displace more than integrate other populations. The take
over may have taken a hundred thousand years. The initial population
may have been a lot smaller than 1,000 individuals with the fusion, but
they would have picked up genetic variation from surrounding
populations, but the gene flow would be restricted.

Ron Okimoto

[JTEM]

Post by RonO
The estimate for when this bottleneck occurred has been going back
further in time for decades.

Do the Google. There was a major impact event or events roughly
800k years ago. Events of that nature had to produce a severe
climate catastrophe. Had to. This was not optional.

Major impacts can be (and many sources claim "Are") worse than
a super volcanic eruption, because the energy is released all
at once instead of over days/weeks/months.

So we have a bottleneck that is literally carved in stone. It's
there, the evidence exist preserved in the earth's layers. And
yet your source isn't finding the slightest <pun> Impact </pun>
on human evolution, though it swears to find an evolutionary
bottleneck.... just not this one.

It's stupid.

Molecular dating sucks rotten eggs through a straw. It just
does. It exaggerates age, often times wildly so. We would
anticipate and even predict that any genetic consequences to
the impact event would look older than it really was.

The only mystery here is WHY people insist on pretending otherwise.