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#15594 - 10/17/06 07:58 AM Re: Neanderthal DNA illuminates split with humans
samwik Offline
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Registered: 10/10/06
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TTNZ, cool
While I thought the article was interesting, I don't agree with it's conclusions. Firstly it, http://human-nature.com/nibbs/02/frost.html, starts out with "Long intense sunlight favoured a lush growth of mosses, lichens, grasses, and low shrubs that fed mammoths, reindeer, bison, and horses. Despite this high bioproductivity, the loess-steppe confronted...."

It may be long intense sunlight, but it's a lot less intense than in Africa. That is why depigmentation was highly selected for. Vit.D comes from sunlight (synthesized via), not meat. Sunlight degrades folic acid (or folate) and so pigmentation is highly selected for in the African environs. ...and yes, through the wisdom of intelligent design, the dark skin is just dark enough to protect the folate but still make vit.D in Africa & vice versa for the light skin up North.
Lack of folate causes birth defects. Actually I think light skins need to supplement with folate a bit (leafy greens). Musta been hard in the winter months. Maybe all those hair colors came from the increased birth defects.

...and what's this stuff about white hair??
also...dark skin tans too. I think tanning is not a recent adaptation.
I think we follow the same rules, everything is consistent; although I'm sure cultural and psychological selection pressures have added some new rules.

I'll have to read those articles more thoroughly before I post them next time. I can usually follow technical explanations, but I didn't understand any of that genetic stuff.
Thanks,
~Sam
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

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#15595 - 10/17/06 02:31 PM Re: Neanderthal DNA illuminates split with humans
TheFallibleFiend Offline
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I'm not sure how much comparison there is between hair color in humans and fur color in dogs, but here goes. I saw a program on dog evolution some months back: http://www.pbs.org/wgbh/nova/dogs/about.html

It reported on an interesting experiment on foxes that occurred in Russia. They were attempting to produce less ferocious foxes they could release in the wild, but surprisingly they produced foxes with many colors and different sizes, as well. (That was a very small part of the entire program.)

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#15596 - 10/17/06 06:45 PM Re: Neanderthal DNA illuminates split with humans
TheFallibleFiend Offline
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More info on the fox experiment:
http://abc.net.au/animals/program1/factsheet5.htm

---

More info on the program from a post I made some time ago on another board:

My daughter and I watched a show about dog evolution on NOVA last night. It was narrated by John Lithgow. Very interesting stuff. The scientists interviewed scoffed at the idea that humans adopted, then domesticated wolves.

Their reasoning goes like this:

1) Dog training and selective breeding are very difficult. They require a lot of resources and some sophisticated knowledge.

2) While archaeological evidence shows that humans and dogs have cohabited for at least 15,000 years, genetic clock evidence indicates that the dog line goes back about 100,000 years.

3) Dog's brains are smaller than wolves' brains.

From these facts some researchers conclude that dogs became at least partially domesticated BEFORE humans adopted them. They suggest that as early human groups began to throw away garbage, some wolves filled a niche by becoming scavengers. (Scavengers generally have smaller brains than predators.) Those scavengers had an evolutionary advantage over the wilder ones who had to struggle much harder to get their food. Over generations, populations of these animals gradually lost their fear of humans and lived alongside them. That is, they became dogs in this process.

An interesting factoid from the show: the earliest dogs seemed to be playthings for royalty and looked a lot like modern salukis.

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#15597 - 10/18/06 03:52 AM Re: Neanderthal DNA illuminates split with humans
terrytnewzealand Offline
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Admittedly a biased source but it's the only link I've found at short notice:

http://www.beefyandlamby.co.uk/red-meat.html

One thing we can be sure of. Meat made up a substantial portion of the ancient human diet in Europe. Also I recall that modern vitamin D deficiency does occur in black-skinned people in Europe these days but only in those whose culture demands they cover up in an unnatural manner. Selection for white skin is unlikely to have anything to do with vit. D.

Re. colour change in domesticated animals. I've been aware of the fox phenomenon for some years. Many of the genes were probably already present as recessives in the wild population. They have been able to survive as double recessives through lack of selection pressure. In the wild there is an advantage for animals to look much the same as each other. Any that stand out are likely to be predated quickly. Likewise for animals that are less afraid. Once a colour variation is established in a domestic population there is no selection to eliminate it. The question for hair colour variation in humans is who domesticated them? Was it each other?

I agree totally with the idea that dogs entered human society on their own initiative.

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#15598 - 10/18/06 04:15 AM Re: Neanderthal DNA illuminates split with humans
samwik Offline
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Loc: Colorado
TerryT: regarding the part of your reply: "Selection for white skin is unlikely to have anything to do with vit. D."

I found a 2002 Scientific American article (although I know they can be wrong, as with the shower-curtain effect). It is entitled Skin Deep: Throughout the world, human skin color has evolved to be dark enough to prevent sunlight from destroying the nutrient folate but light enough to foster the production of vitamin D. At <http://www.sciam.com/article.cfm?articleID=000B7732-FC72-1D80-90FB809EC5880000>
~The first paragraph ends with: "Recent epidemiological and physiological evidence suggests to us that the worldwide pattern of human skin color is the product of natural selection acting to regulate the effects of the sun?s ultraviolet (UV) radiation on key nutrients crucial to reproductive success."
Not definitive, but certainly plausible I think.
Thanks,
~Sam
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

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#15599 - 10/19/06 03:25 AM Re: Neanderthal DNA illuminates split with humans
terrytnewzealand Offline
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Loc: Whangarei New Zealand
The theory is fine but several questions then arise. Why didn't the same thing happen throughout Northern Eurasia? Why did selection for a white skin colour occur predominantly in the region of northern deciduous forest, a region where the trait is found in many other species? Is the balance between folate and vitamin D that precarious? Wouldn't humans have been fully-clothed by the time they reached north far enough for it to matter?

Re. the pervasive influence of Judeo-Christian beliefs. The Basque philosopher Unamuno recognised the problem when he said that in Spain even atheists are Catholic.

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#15600 - 10/19/06 03:42 AM Re: Neanderthal DNA illuminates split with humans
samwik Offline
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I think the changes in skin color took place 50-30 Kya. The exceptions to the theory would be populations that more recently moved to "wrong" latitudes such as the native Americans. Maybe a white, reflective environment fosters darker skin also, like the eskimos (though they are relatively recent too). I'm just speculating here.

ROFL with "The Basque philosopher Unamuno recognised the problem when he said that in Spain even atheists are Catholic."

Thanks alot,
~Sam
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

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#15601 - 10/19/06 06:54 AM Re: Neanderthal DNA illuminates split with humans
terrytnewzealand Offline
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Loc: Whangarei New Zealand
Samwik. Your comments re. reflective environments are widely accepted. East Asians evidently have very little melanin but plenty of keratin in their skin. This reflects sunlight very effectively. The East Asian eyes shape also indicates a reflective environment. Where might these characteristics have evolved? My guess is in the high altitudes of what is now Western China and Mongolia. Both white skin and these East Asian features presumably developed before people had clothes. What evidence do you have they developed only as recently as 50,000 years ago?

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#15602 - 10/19/06 08:01 AM Re: Neanderthal DNA illuminates split with humans
samwik Offline
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Registered: 10/10/06
Posts: 1164
Loc: Colorado
Okay, just speculation based on the 70Kya date for 'out of Africa' & a 20,000 year time period needed for skin color shift. I'm sure I recall the 20K figure, and I think I heard of that on the PBS Nova program on the Vit.D/folate theory.
I also allowed 20K years for migration first, but this selection is always happening. I imagine that at some point ~60-30Kya populations became stable enough in one region that color shift took place. I probably should have said 40-30Kya +/-20K years.
Neat info. about the keratin and eyes too.
Thanks,
~samwik
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

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#15603 - 10/19/06 08:15 AM Re: Neanderthal DNA illuminates split with humans
samwik Offline
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Registered: 10/10/06
Posts: 1164
Loc: Colorado
I thought that was interesting stuff above, about the dogs too.

re: "some wolves filled a niche by becoming scavengers." -FF
re: "In the wild there is an advantage for animals to look much the same as each other. Any that stand out are likely to be predated quickly. Likewise for animals that are less afraid." -TTNZ

I was struck by a thought after reading the two ideas above. Both of Terry's points, would lead those animals to be shunned, or driven out, by the pack; and, if not predated, could likely become FF's "some wolves [that] filled a niche by becoming scavengers."

~Samwik
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

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#15604 - 10/19/06 02:02 PM Re: Neanderthal DNA illuminates split with humans
soilguy Offline
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Registered: 09/28/05
Posts: 414
Loc: North Carolina
re: Dogs

I think the Nova program attributed the multiple colors "available" in domestic dogs to testosterone levels. Domestic dogs have lower testosterone levels than wolves, which allows pre-existing color variations to be expressed. (The high testosterone levels in wild wolves has a strong influence on the production of dark pigment.) The "new" colors in dogs occur too quickly for them to have arisen through mutations since domestication.
_________________________
When fascism comes to America, it will be wrapped in the flag and carrying the cross."
--S. Lewis

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#15605 - 10/20/06 12:25 AM Re: Neanderthal DNA illuminates split with humans
terrytnewzealand Offline
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Registered: 08/02/06
Posts: 1031
Loc: Whangarei New Zealand
Soilguy wrote:

'The "new" colors in dogs occur too quickly for them to have arisen through mutations since domestication.'

Totally agree. I read information on the foxes years ago and the writer stated the changes started happening within just two or three generations. The genes must have already been present. Testosterone levels could well be implicated in colour change. We know that the effect of any particular gene is seldom as simple as we were taught in school.

I think change becomes rapid once selection is reduced because not only do double recessives survive, new combinations of double recessives survive. Colours and patterns that never appear in the wild population can suddenly appear. I think this is the aspect Trilobyte just can't get his head around when he demands a magical series of changes at the same point on the chromosome.

A relaxing of selection pressure, by definition, allows population numbers to build. Resources usually eventually become fewer and selection rears its head once more. Any change in selection pressure can then lead to rapid change in appearance. Punctuated equilibrium.

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