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Celt_??
07-11-2018, 09:41 PM
Researchers say it is time to drop the idea that modern humans originated from a single population in a single location

The origins of our species have long been traced to east Africa, where the world’s oldest undisputed Homo sapiens fossils were discovered. About 300,000 years ago, the story went, a group of primitive humans there underwent a series of genetic and cultural shifts that set them on a unique evolutionary path that resulted in everyone alive today. However, a team of prominent scientists is now calling for a rewriting of this traditional narrative, based on a comprehensive survey of fossil, archaeological and genetic evidence. Instead, the international team argue, the distinctive features that make us human emerged mosaic-like across different populations spanning the entire African continent. Only after tens or hundreds of thousands of years of interbreeding and cultural exchange between these semi-isolated groups, did the fully fledged modern human come into being.

Dr Eleanor Scerri, an archaeologist at Oxford University, who led the international research, said: “This single origin, single population view has stuck in people’s mind … but the way we’ve been thinking about it is too simplistic.” This continental-wide view would help reconcile contradictory interpretations of early Homo sapiens fossils varying greatly in shape, scattered from South Africa (Florisbad) to Ethiopia (Omo Kibish) to Morocco (Jebel Irhoud). The telltale characteristics of a modern human – globular brain case, a chin, a more delicate brow and a small face – seem to first appear in different places at different times. Previously, this has either been explained as evidence of a single, large population trekking around the continent en masse or by dismissing certain fossils as side-branches of the modern human lineage that just happened to have developed certain anatomical similarities.

The trend towards more sophisticated stone tools, jewellery and cooking implements also supports the theory, according to the paper in the journal Trends in Ecology & Evolution.
Scerri assembled a multidisciplinary group to examine the archaeological, fossil, genetic and climate data together, with the aim of eliminating biases and assumptions. Previously, she said, scientific objectivity had been clouded by fierce competition between research groups each wanting their own discoveries to be given a prominent place on a linear evolutionary ladder leading to the present day. Disputes between rival teams working in South Africa and east Africa had become entrenched, she said.

The latest analysis suggests that this patchwork emergence of human traits can be explained by the existence of multiple populations that were periodically separated for millennia by rivers, deserts, forests and mountains before coming into contact again due to shifts in the climate. “These barriers created migration and contact opportunities for groups that may previously have been separated, and later fluctuation might have meant populations that mixed for a short while became isolated again,” said Scerri. The analysis also paints a picture of humans as a far more diverse collection of species and sub-populations than exists today. Between 200,000 and 400,000 years ago, our own ancestors lived alongside a primitive human species called Homo naledi, found in southern Africa, a larger brained species called Homo heidelbergensis in central Africa and perhaps myriad other humans yet to be discovered.

https://www.theguardian.com/science/2018/jul/11/no-single-birthplace-of-mankind-say-scientists

Shaikorth
11-03-2018, 01:18 PM
Researchers say it is time to drop the idea that modern humans originated from a single population in a single location

The origins of our species have long been traced to east Africa, where the world’s oldest undisputed Homo sapiens fossils were discovered. About 300,000 years ago, the story went, a group of primitive humans there underwent a series of genetic and cultural shifts that set them on a unique evolutionary path that resulted in everyone alive today. However, a team of prominent scientists is now calling for a rewriting of this traditional narrative, based on a comprehensive survey of fossil, archaeological and genetic evidence. Instead, the international team argue, the distinctive features that make us human emerged mosaic-like across different populations spanning the entire African continent. Only after tens or hundreds of thousands of years of interbreeding and cultural exchange between these semi-isolated groups, did the fully fledged modern human come into being.

Dr Eleanor Scerri, an archaeologist at Oxford University, who led the international research, said: “This single origin, single population view has stuck in people’s mind … but the way we’ve been thinking about it is too simplistic.” This continental-wide view would help reconcile contradictory interpretations of early Homo sapiens fossils varying greatly in shape, scattered from South Africa (Florisbad) to Ethiopia (Omo Kibish) to Morocco (Jebel Irhoud). The telltale characteristics of a modern human – globular brain case, a chin, a more delicate brow and a small face – seem to first appear in different places at different times. Previously, this has either been explained as evidence of a single, large population trekking around the continent en masse or by dismissing certain fossils as side-branches of the modern human lineage that just happened to have developed certain anatomical similarities.

The trend towards more sophisticated stone tools, jewellery and cooking implements also supports the theory, according to the paper in the journal Trends in Ecology & Evolution.
Scerri assembled a multidisciplinary group to examine the archaeological, fossil, genetic and climate data together, with the aim of eliminating biases and assumptions. Previously, she said, scientific objectivity had been clouded by fierce competition between research groups each wanting their own discoveries to be given a prominent place on a linear evolutionary ladder leading to the present day. Disputes between rival teams working in South Africa and east Africa had become entrenched, she said.

The latest analysis suggests that this patchwork emergence of human traits can be explained by the existence of multiple populations that were periodically separated for millennia by rivers, deserts, forests and mountains before coming into contact again due to shifts in the climate. “These barriers created migration and contact opportunities for groups that may previously have been separated, and later fluctuation might have meant populations that mixed for a short while became isolated again,” said Scerri. The analysis also paints a picture of humans as a far more diverse collection of species and sub-populations than exists today. Between 200,000 and 400,000 years ago, our own ancestors lived alongside a primitive human species called Homo naledi, found in southern Africa, a larger brained species called Homo heidelbergensis in central Africa and perhaps myriad other humans yet to be discovered.

https://www.theguardian.com/science/2018/jul/11/no-single-birthplace-of-mankind-say-scientists

This is basically the (within) African multiregionalism, Razib Khan wrote (https://www.gnxp.com/WordPress/2018/07/17/the-new-african-multi-regionalism/) a bit more on that.
Could be none of the African hominids survived as long as Neanderthals and Denisovans so we are still ways away from getting DNA evidence for it. At least in the scientific community it would be a bomb if it turns out that, let's say, 20% of modern humans is from the Heidelbergensis branch given how much attention 2% Neanderthal in OOA modern humans did.

Kale
11-05-2018, 12:27 AM
Wouldn't we expect a deeper MRCA for modern uniparental markers if this were the case? Certainly much deeper than autosomal divergences at least.
Isn't it actually the other way around? The South_Africa_2000BP samples having an estimated autosomal divergence from Eurasians of ~260,000 years, but with uniparental markers only ~150,000 or so diverged?
I could envision a modern human population existing in a single region of Africa, then periodically gaining contact with neighboring hominids via climate cycles.
Lineages could filter out of the population just fine if it was a small enough pulse each time the mixture occurred.
This would account for autosomal divergence being deeper than uniparental.

FIREYWOTAN
11-19-2018, 03:01 PM
Thanks for sharing an interesting interpretation. So much has hinges on the answers makes the whole issue confusing at best. Yet at times it seems we all want an answer to that question.
The thoughts of a series of starts and stops can't be overlooked especially with the Ancient DNA that seems to be found in so many places. The truth is an interesting way
to challenge what it is that's already been challenged. Recently " Dragon Bone Hill" by Boaz and Ciochon made a case for Homo erectus especially with just how much evidence is spread over the world at lodge.
The next moment
]This is basically the (within) African multiregionalism, Razib Khan wrote a bit more on that.
Could be none of the African hominids survived as long as Neanderthals and Denisovans so we are still ways away from getting DNA evidence for it. At least in the scientific community it would be a bomb if it turns out that, let's say, 20% of modern humans is from the Heidelbergensis branch given how much attention 2% Neanderthal in OOA modern humans did.

Just have to wonder what would be wrong if multiple starts and stops were the rule and exception.
[/B]

Saad2016
11-29-2018, 09:21 PM
very interesting. So could it be implied that not necessarily all modern humans originated from a single parent . If that is true then the whole Y DNA tree/branching out of various haplogroups in different periods of time will be questionable ?

GailT
12-02-2018, 04:49 AM
Wouldn't we expect a deeper MRCA for modern uniparental markers if this were the case? Certainly much deeper than autosomal divergences at least. Isn't it actually the other way around? The South_Africa_2000BP samples having an estimated autosomal divergence from Eurasians of ~260,000 years, but with uniparental markers only ~150,000 or so diverged?
I could envision a modern human population existing in a single region of Africa, then periodically gaining contact with neighboring hominids via climate cycles. Lineages could filter out of the population just fine if it was a small enough pulse each time the mixture occurred. This would account for autosomal divergence being deeper than uniparental.

For y-DNA, the MRCA is closer to 300,000 years ago, with the discovery of A00. It is also possible that a population bottleneck around 200,000 years ago could have contributed to a loss of diversity in y-DNA and mtDNA haplogroups.

Kaipiro
12-08-2018, 02:30 PM
For y-DNA, the MRCA is closer to 300,000 years ago, with the discovery of A00. It is also possible that a population bottleneck around 200,000 years ago could have contributed to a loss of diversity in y-DNA and mtDNA haplogroups.

I read somewhere that A00 could not be modern human, but an archaic hominin that interbred with HS, at least it is suggested so, because it's so different and old, predating HS.

Cosmo
06-06-2019, 12:43 PM
For y-DNA, the MRCA is closer to 300,000 years ago, with the discovery of A00.

I have heard that a lot but it is based on the calculations by Menendez in 2013. In 2014 Elhaik came out with a study the next year which I think devastated that claim, and came up with an age of 208,000. IOW barely older than the other "A" haplogroups. I know Eran Elhaik is a controversial figure in the field, but not because his science is bad rather because he takes on controversial topics and thinks outside the box. I have never seen a refutation of Elhaik's paper demolishing the claims of Menendez about the antiquity of A00. Why does the media just ignore it and repeat the claims of Menendez? Here is the Elhaik study..

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4135414/

xenus
06-06-2019, 05:28 PM
I have heard that a lot but it is based on the calculations by Menendez in 2013. In 2014 Elhaik came out with a study the next year which I think devastated that claim, and came up with an age of 208,000. IOW barely older than the other "A" haplogroups. I know Eran Elhaik is a controversial figure in the field, but not because his science is bad rather because he takes on controversial topics and thinks outside the box. I have never seen a refutation of Elhaik's paper demolishing the claims of Menendez about the antiquity of A00. Why does the media just ignore it and repeat the claims of Menendez? Here is the Elhaik study..

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4135414/

There is never a "last word" on a topic like this and since that paper there have been others like
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520482/

Cosmo
06-06-2019, 07:48 PM
There is never a "last word" on a topic like this and since that paper there have been others like
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520482/

Thank you for that link. I found it quite interesting. Some very curious stuff in there, like....


Finally, we compared recent and deep branches of the tree, expecting the latter to display a stronger dependency of the density of variants on gene content as they were exposed to the action of purifying natural selection for longer times and in large sectors of the population. Our results went in the opposite direction (S3 Table).

So the extra mutations in A00 for example don't seem to have been subject to purifying selection. That's hardly consistent with the idea that they were a non-Sapien introgression. Y-DNA is a desert for Neanderthal genes for example. Something does not add up here.


It is possible that different social habits, lifestyles and environmental conditions experienced by populations harbouring different haplogroups resulted in systematic variations of the generation time and average paternal age at conception [8]. These have been suggested to affect differentially replication-dependent and non-dependent mutations, altering their relative proportions [9, 19].

Very possible. Documented even. Which is why it doesn't make sense to use a North Asian and Northern European from frigid climates to calculate mutation rates for Africans 200,000 years ago.

I am still open, but so far I haven't seen anything which convinces me that that A00 is substantially older than 200K.

xenus
06-07-2019, 12:16 AM
Thank you for that link. I found it quite interesting. Some very curious stuff in there, like....



So the extra mutations in A00 for example don't seem to have been subject to purifying selection. That's hardly consistent with the idea that they were a non-Sapien introgression. Y-DNA is a desert for Neanderthal genes for example. Something does not add up here.



Very possible. Documented even. Which is why it doesn't make sense to use a North Asian and Northern European from frigid climates to calculate mutation rates for Africans 200,000 years ago.

I am still open, but so far I haven't seen anything which convinces me that that A00 is substantially older than 200K.

Yfull's estimate is "formed 235900 ybp"
their FAQ about their age estimation methodology links to this paper https://www.researchgate.net/publication/273773255_Defining_a_New_Rate_Constant_for_Y-Chromosome_SNPs_based_on_Full_Sequencing_Data

I think if you were to want to do a practical estimate that far back in time you'd have to estimate mutation rates using only ancient samples under the assumption that it's non linear. Samples from varying archaeological cultures dating to after the advent of settled life would have to be examined separately because settled life at least increases the likelyhood that paternal age will increase either on average or with enough frequency that it could increase the mutation rate and this phenomena is likely to be very uneven between cultures if the modern variation is anything to go by.

Two papers, one from an institute i'm not familiar with and one from Reich's lab (he was involved in both)

https://www.simonsfoundation.org/2016/09/21/genome-diversity-project-reveals-faster-accumulation-of-mutations-in-non-africans/

https://reich.hms.harvard.edu/sites/reich.hms.harvard.edu/files/inline-files/2015_NG_Do_Deleterious_Load_Concatenated_1.pdf

TuaMan
06-07-2019, 12:32 AM
Other than parental age at conception, what are some other variables that could impact mutation rates?

xenus
06-07-2019, 04:08 AM
Population growth would be the first thing I can think of and definitely one of the biggest.

Some plants contain mutagens. Cooking can create and/or release mutagens as well so the shift to cooking our food that
played a big part in our early history is likely to have increased mutations. If they cause germ line mutations that can be passed on would require looking at it in more detail but I think it's highly likely that certain groups would take up certain foods or cooking methods that would cause germ cell mutations.

I don't know if it's ever been tested or demonstrate but I'd bet that exposure to most kinds of smoke can cause mutations with enough exposure. Not to the levels of say cigarette smoke but burning fields or daily exposure to incense might do it.

Exposure to radiation https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0041300
exposure to radon in caves and then later on when humans began mining.

Those are the things that came to mind but i know there are others i'm missing.