https://phys.org/news/2023-09-skepticism-human-ancestors-extinct.html
Phys.org has an article up noting skepticism among human population geneticists about the recent claims that humans may have suffered a population bottleneck so narrow that only around 1,300 individuals left descendants in the current modern human population. The estimated time
of the bottleneck was around 900,000 years ago. At least a hundred
thousand years before Neanderthals and Denisovans split off from the
Homo that remained in Africa.
Mostly the claims seem to be that the estimate can't be as precise as
the 1,280 individuals estimated in the paper. The article seems to
ignore all the previous claims of a genetic bottleneck for the human lineage. Human geneticists have been trying to explain why modern
humans have around 1/5 the genetic diversity as a normal species. Even chimps and gorillas, as decimated as their populations have become, have over 3 times the genetic diversity observed in extant humans.
The genetic diversity in the current human population is vast. Just in
the extant population every site on the genome of 3 billion bps has
likely been hit by a new mutation on the order of 100 times, due to the billions of humans in existence, but when population geneticists talk
about segregating genetic variation they are referring to genetic
variation with an allele frequency of, at least, 0.01. This just means
that Modern humans are deficient in genetic variation that is found in
at least 2 out of 100 people, so recent mutations are excluded from the analysis. Only genetic variants that can be found in a significant
portion of the population are counted.
The first claim to a bottleneck involving on the order of 1,000
individuals contributing genetics to the current population was when we first had less than a hundred genomes to look at. The claim that I
recall was that the bottleneck may have occurred within the last 100,000 years, but the study was deficient in African genomes, and "bottleneck"
may have reflected the small subpopulation that had managed to make it
out of Africa within the last 80,000 years.
The subsequent bottleneck estimates that I recall kept pushing the time
of the bottleneck further and further back in time as more African
genomes were added to the database.
What I note is that none of the critics, seem to put forward the
speciation event possiblity that I put up when this research was first published. The chromosome 2 fusion event is estimated to have occurred around 900,000 years ago, and there could have been reduced geneflow
into the population that had the fusion event. There could have been a
lot of other Homo around, but hybrids could have been selected against.
This would have reduced gene flow between populations and would have
been a sympatric speciation event. The speciation event would have been
over by the time Neanderthals and Denisovans left Africa and took the chromosome 2 fusion with them around 800,000 years ago. The Neanderthal genomes also indicate a population bottleneck in their past, and it may
be the same population bottleneck.
Ron Okimoto
https://phys.org/news/2023-09-skepticism-human-ancestors-extinct.html
Phys.org has an article up noting skepticism among human population >geneticists about the recent claims that humans may have suffered a >population bottleneck so narrow that only around 1,300 individuals left >descendants in the current modern human population. The estimated time
of the bottleneck was around 900,000 years ago. At least a hundred
thousand years before Neanderthals and Denisovans split off from the
Homo that remained in Africa.
Mostly the claims seem to be that the estimate can't be as precise as
the 1,280 individuals estimated in the paper. The article seems to
ignore all the previous claims of a genetic bottleneck for the human
lineage. Human geneticists have been trying to explain why modern
humans have around 1/5 the genetic diversity as a normal species. Even >chimps and gorillas, as decimated as their populations have become, have
over 3 times the genetic diversity observed in extant humans.
The genetic diversity in the current human population is vast. Just in
the extant population every site on the genome of 3 billion bps has
likely been hit by a new mutation on the order of 100 times, due to the >billions of humans in existence, but when population geneticists talk
about segregating genetic variation they are referring to genetic
variation with an allele frequency of, at least, 0.01. This just means
that Modern humans are deficient in genetic variation that is found in
at least 2 out of 100 people, so recent mutations are excluded from the >analysis. Only genetic variants that can be found in a significant
portion of the population are counted.
The first claim to a bottleneck involving on the order of 1,000
individuals contributing genetics to the current population was when we
first had less than a hundred genomes to look at. The claim that I
recall was that the bottleneck may have occurred within the last 100,000 >years, but the study was deficient in African genomes, and "bottleneck"
may have reflected the small subpopulation that had managed to make it
out of Africa within the last 80,000 years.
The subsequent bottleneck estimates that I recall kept pushing the time
of the bottleneck further and further back in time as more African
genomes were added to the database.
What I note is that none of the critics, seem to put forward the
speciation event possiblity that I put up when this research was first >published. The chromosome 2 fusion event is estimated to have occurred >around 900,000 years ago, and there could have been reduced geneflow
into the population that had the fusion event. There could have been a
lot of other Homo around, but hybrids could have been selected against.
This would have reduced gene flow between populations and would have
been a sympatric speciation event. The speciation event would have been
over by the time Neanderthals and Denisovans left Africa and took the >chromosome 2 fusion with them around 800,000 years ago. The Neanderthal >genomes also indicate a population bottleneck in their past, and it may
be the same population bottleneck.
Mostly the claims seem to be that the estimate can't be as precise as
the 1,280 individuals estimated in the paper. The article seems to
ignore all the previous claims of a genetic bottleneck for the human
lineage. Human geneticists have been trying to explain why modern
humans have around 1/5 the genetic diversity as a normal species. Even
chimps and gorillas, as decimated as their populations have become, have
over 3 times the genetic diversity observed in extant humans.
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