a DNA question

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a DNA question

Postby Athena on October 18th, 2016, 10:39 pm 

How is it possible that indigenous sub-Africans have no Neanderthal DNA?



https://genographic.nationalgeographic.com/neanderthal/

A team of scientists comparing the full genomes of the two species concluded that most Europeans and Asians have between 1 to 4 percent Neanderthal DNA. Indigenous sub-Saharan Africans have no Neanderthal DNA because their ancestors did not migrate through Eurasia.
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Re: a DNA question

Postby BadgerJelly on October 19th, 2016, 12:30 am 

Because Neanderthals lived in cooler climates. Maybe they do have traces it is just too small to tell.
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Re: a DNA question

Postby Athena on October 19th, 2016, 9:24 am 

Okay, I understand chickens have the DNA for teeth, but not all DNA this DNA remains dormant. Dogs look different because if we breed for one change that can result in 4 changes, like a flatter face and wagging tail. I thought the original gene pool was very large with some being activated and others remaining dormant. But the original gene pool for Neanderthals is different from the source of that gene pool. Somehow the Neanderthals picked up new genes? This is what I am not understanding?
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Re: a DNA question

Postby Forest_Dump on October 19th, 2016, 9:57 am 

I suppose this might be a bit complicated but I will try to give a simple answer although on a few things I am probably a bit out of date. Our ancestors evolved in sub-Saharran Africa but various groups have been migrating out for probably millions of years a sometimes later groups did cross-breed with groups already out in the rest of Europe and Asia. A line of ancestors that later became us first appears in Africa and is called archaic Homo sapiens. Some stayed in Africa but some also left Africa and also spread throughtout Asia and Europe and probably also interbred with groups that had left earlier. All of these continued to evolve sperately from each other which basically means their DNA changed for various reasons including that they lived in seperate areas and so natural selection worked differently on these different groups. One group living in Europe and northwestern Asia became what most call Neandethals. While Neanderthals were evolving and living in northern Europe, the group that most directly became us was still in sub-saharran Africa evolving seperately and became what we call anatomically modern Homo sapiens. Later some of these people also left Africa and some of them moved into Europe where the Neanderthals were and it appears some of them interbred with Neanderthals and that is how some of them picked up a bit of Neanderthal DNA. But of course this DNA would not be passed back to the people who stayed in more southern (sub-saharran) Africa. This is pretty simplistic but gives you the outline - I hope.
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Re: a DNA question

Postby Athena on October 19th, 2016, 11:39 am 

Forest_Dump » October 19th, 2016, 7:57 am wrote:I suppose this might be a bit complicated but I will try to give a simple answer although on a few things I am probably a bit out of date. Our ancestors evolved in sub-Saharran Africa but various groups have been migrating out for probably millions of years a sometimes later groups did cross-breed with groups already out in the rest of Europe and Asia. A line of ancestors that later became us first appears in Africa and is called archaic Homo sapiens. Some stayed in Africa but some also left Africa and also spread throughtout Asia and Europe and probably also interbred with groups that had left earlier. All of these continued to evolve sperately from each other which basically means their DNA changed for various reasons including that they lived in seperate areas and so natural selection worked differently on these different groups. One group living in Europe and northwestern Asia became what most call Neandethals. While Neanderthals were evolving and living in northern Europe, the group that most directly became us was still in sub-saharran Africa evolving seperately and became what we call anatomically modern Homo sapiens. Later some of these people also left Africa and some of them moved into Europe where the Neanderthals were and it appears some of them interbred with Neanderthals and that is how some of them picked up a bit of Neanderthal DNA. But of course this DNA would not be passed back to the people who stayed in more southern (sub-saharran) Africa. This is pretty simplistic but gives you the outline - I hope.


I tried to get the desired information with a google search and was overwhelmed. Your simpler explanation of archaic Homo sapiens clears up part of the confusion. Not understanding what was meant by archaic Homo sapiens, was driving me crazy!

But now I have a burning question. Why would the conditions in Africa lead to modern man, and not the conditions in the north? Exactly how are our environments impacting us, making us different?
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Re: a DNA question

Postby Forest_Dump on October 19th, 2016, 12:05 pm 

Athena wrote:Why would the conditions in Africa lead to modern man, and not the conditions in the north? Exactly how are our environments impacting us, making us different?


Well that is a good question actually but one that would inevitably take us into much more controversial areas and so I will quickly bow out of the discussion. Suffice to say that some of the answer has to take us into considering trends over a much longer span of time (back to millions of years) and include all kinds of changes ranging from posture to the size and shape of the brain and skull, heaviness of brow ridges, etc. For some thngs like skin colour and/or hairiness we have little direct evidence from the past but might have some kinds of evidence from DNA. Some of these things might be directly linked together but others might be independent and coincidental and it is often tough to tell for sure if these things are not directly reflected in surviving bones. And we need to remember that surviving bones often are not common enough from all the areas and times that could be of help in adressing these questions. And some prefer, for example to try to answer these questions strictly from arguments of natural selection while others (like me) often prefer to look more at things like more random processes like genetic drift. Bottom line here, we go with what evidence we have, i.e., that it did happen in southern Africa based on the evidence we have now and deal with that until more and better evidence comes along and/or more and better lines of argument and explanation that can be tested in other ways. Obviously lots of new evidence has been coming from studies of modern and (very) rare (and fragmentary) and these are independent from what lines of evidence comes from fossil bones (which almost never have DNA) and the two lines of independent evidence are beeing looked at and interpreted together. Things will still change as more from both areas are brought to light and adjusted as we go.
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Re: a DNA question

Postby Athena on October 23rd, 2016, 12:46 pm 

Forest_Dump » October 19th, 2016, 10:05 am wrote:
Athena wrote:Why would the conditions in Africa lead to modern man, and not the conditions in the north? Exactly how are our environments impacting us, making us different?


Well that is a good question actually but one that would inevitably take us into much more controversial areas and so I will quickly bow out of the discussion. Suffice to say that some of the answer has to take us into considering trends over a much longer span of time (back to millions of years) and include all kinds of changes ranging from posture to the size and shape of the brain and skull, heaviness of brow ridges, etc. For some things like skin colour and/or hairiness we have little direct evidence from the past but might have some kinds of evidence from DNA. Some of these things might be directly linked together but others might be independent and coincidental and it is often tough to tell for sure if these things are not directly reflected in surviving bones. And we need to remember that surviving bones often are not common enough from all the areas and times that could be of help in adressing these questions. And some prefer, for example to try to answer these questions strictly from arguments of natural selection while others (like me) often prefer to look more at things like more random processes like genetic drift. Bottom line here, we go with what evidence we have, i.e., that it did happen in southern Africa based on the evidence we have now and deal with that until more and better evidence comes along and/or more and better lines of argument and explanation that can be tested in other ways. Obviously lots of new evidence has been coming from studies of modern and (very) rare (and fragmentary) and these are independent from what lines of evidence comes from fossil bones (which almost never have DNA) and the two lines of independent evidence are beeing looked at and interpreted together. Things will still change as more from both areas are brought to light and adjusted as we go.


Please, come back and answer if you will, what was the environment like in southern Africa? I have a book that argues our breast and speech is the result of a lot of time in water. Climate change in south Africa would mean drought and a change from rain forest to open plains, which some claim lead to us walking upright. We know some archaic humans went north and traveled into Europe and Asia and that others stayed in south Africa. South Africa has a lot of coast line and looks like an ideal place to be for an archaic human that can swim, and like dolphins and whales and birds develop vocal communication, and boobs that float and can feed an infant, while the mother is gathering food and staying cool. What do you think?
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Re: a DNA question

Postby Forest_Dump on October 28th, 2016, 1:20 pm 

I will need to seperate some of the questions here to give a bit more context.

Athena wrote: I have a book that argues our breast and speech is the result of a lot of time in water.


Yes there was a book written back in the late 1970's that made the argument for the aquatic hypothesis as I think it was called. So, the first point would be that this idea has been largely discredited and I think there is even a thread here somewhere on the topic. Just to recap what we now know or infer, bipedalism (walking on two feet) happened probably 5 million years ago (give or take a million allowing for some debate) while archaic Homo sapiens appear 250,000 (+/-) and anatomically modern Homo sapiens 100,000 (+/-), Neanderthals probably less that 50,000 years ago (depending on what you count as Neanderthal, etc.) so very different scales of time. Depending on what you count as speech, that may be earlier or later than bipedalism. Human-like breasts may be (probably?) later than bipedalism but that too depends on what counts plus the fact that there is little evidence to go on. But the aquatic hypothesis doesn't really stand up for anyone serious on the topic.

Athena wrote:Climate change in south Africa would mean drought and a change from rain forest to open plains, which some claim lead to us walking upright.


Yes the climate changed a lot over different times and climate change certainly does play a role and needs to be taken into account in virtually all explanatory hypotheses (although maybe not so much in an "alien-tinkering" hypothesis but again suffice to say that is not a serious one).
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Re: a DNA question

Postby Athena on October 29th, 2016, 2:04 pm 

I am not so ready to give up the aquatic hypothesis without more evidence for why I should do so. However, I find my mind jumping to an altered explanation. I can image how depending on water sources of food, might lead to venturing further into the water, and then a floating device and then using water and a floating device for transportation, each step expanding the brain's capability to process information. I am adjusting my first assumption to reaffirm water played an important part our development.

Vaguely remembering something I read about how experiences are carried in our genes, I looked for more information.

http://discovermagazine.com/2013/may/13 ... your-genes

According to the new insights of behavioral epigenetics, traumatic experiences in our past, or in our recent ancestors’ past, leave molecular scars adhering to our DNA. Jews whose great-grandparents were chased from their Russian shtetls; Chinese whose grandparents lived through the ravages of the Cultural Revolution; young immigrants from Africa whose parents survived massacres; adults of every ethnicity who grew up with alcoholic or abusive parents — all carry with them more than just memories.


What do you think?
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