Posted on 05/14/2005 7:58:39 AM PDT by Lessismore
The theory is that in order for less and less sunlight available as people moved north to make vitamin D, their skin lost melanin. In the early part of the last century (before vitamin D fortification of milk) an outbreak of rickets (D deficiency disease) occurred in Chicago among African American infants because they did not get enough sun.
As far as modern human evolution goes, the key is the isolation of a population. With all the genetic mixing nowadays, it would be hard for much genetic change over time to only affect certain populations.
I thought this bit was interesting: We hope that the new findings will inspire archaeological exploration between the Arabian Peninsula and Southeast Asia in search of the remains of the first Eurasians 50,000 to 100,000 years ago.
I know there's a lot of digs on the Sub-Continent, but what about the Arabian Peninsula?
But the children of the ones that went North died out, while the children of the ones that went South continue to reproduce, to this day.
That's the point of the story. You, I, and everybody else on Earth, are the descendents of the ones who went South. At least, this is what DNA is telling us.
We don't know what color the original Africans were. They may have had lighter skin and straighter hair than present day Africans, and got darker while everybody else got lighter.
Good point. The 'stay-at-home' Africans may have gone through their own series of changes that were different than those that affected the 'out-of-Africans.' The sub-Saharan Africans are the most 'different' from all the other people outside that region.
I googled on this topic and found the following article: The Biology of Skin Color. What's interesting is that there are at least two real feedback mechanisms (ie. ones that affect survival) due to ultraviolet sunlight: vitamin B and D. Nowadays, women when they're anticipating pregnancy, are advised to take B in prenatal vitamins to help reduce neural tube defects. Vitamin D is the rickets.
The article says that the earliest humans in Africa (pre-modern humans) were lighter skinned but as they lost body hair became darker skinned to reduce exposure to strong ultraviolet sunlight. Why? Because UV light decreases the amount of B in a woman's body, leading to more neural tube defects in children. IOW, there was evolutionary pressure in favor of darker skin and inhibiting lighter skin. This pressure goes away in Europe.
The UV connection with Vitamin D has the evolutionary pressure favoring lighter skin in Europe because D is needed for strong bone growth. Dark skin blocks UV from the Sun, leading to weaker bones in lower-light climates like Europe.
This all sounds perfectly plausible. I don't have the biological credentials to judge whether its accurate or not. Still, are these two pressures strong enough to produce such significant changes in only 30K years???
Yes, that's what the article I found assumes. The earliest humans (pre-modern man), were lighter skinned but had much more hair. As the amount of hair decreased, the skin darkened to reduce overall UV exposure. The mechanism was intense UV sunlight destroying vitamin B (folic acid) in lighter skinned, pregnant women's bodies, thus causing neural tube defects in babies.
Note: apparently there are documented cases of white women using tanning salons while pregnant and having NTD babies possibly due to the reduced B. The bad thing is that B is most important in the early stages of a PG, before it becomes obvious. Yikes!
As I understand the studies, a very large majority of European and North African (semetic?) people share a common marker. That marker is not found in others, so a break away by people of common heritage is implied.
Further, it is possible (?) to crudely date the arrival of that marker in places that form a pathway out of Africa, into the middle east & south china, and then into europe. Other studies have identified migration of he same marker into south America at a date well before the advent of "Native Americans" because...
The native americans appear to have used a different and later route which can also be mapped using similar tracking methods to map a different mtDNA marker.
I don't see much of a hoax in that and the possibility that both male and female ancestors might contribute to mtDNA is a red herring - if a marker exists and can be passed on, it seems a valid clue.
It is, after all, merely informed guess work.
According to anthropologist Marvin Harris (bless his soul), yes. He said that at some point both these features became sexual preferences. In Europe, lighter skin produced healthier babies and light skin became beautiful. The opposite was occurring in Africa where those with lighter skin were getting ugly and deadly skin cancer and blacker became beautiful.
In ancient times, due to starvation, mothers would have to choose which child to feed and save...they would choose the healthier. There were many such pressures working on skin pigmentation.
The African Bushmen are physically different than all other humans on earth. The females have an 'apron' over the genetial area and the males have a semi-erect penis. Also, the Bushmen are lighter skinned, have some features resembling Mongoloids and their children even have 'Mongoloid spots' which is common among the Asians of today. (The 'spots' disappear with age on all)
Seems like very good speculation. It provides a mechanism to favor specific characteristics *and* inhibit others. I think the main problem in teaching evolution is the way it's described. Evolution, imho, is due to the killing off of less favored by pressure. Europeans aren't white because they developed that way, its that the ones with darker skin died off. The reverse is true in equatorial regions. I think that current Evolution teaching implies that the genes of offspring are *changed* by the evolutionary pressure.
I guess the thing I wonder about most is this: what evolutionary pressures are working today? Who is being favored by them? When will the next jump occur (like that from pre-modern to modern man)? Will it be natural or manmade?
That is good. But it places the birth of agriculture in a different spot than I thought.
You're confusing the data with the popular presentation. The latter is a hoax, regardless of your unfamiliarity with it.
Fascinating stuff. I read up on the Khosians. When showed pictures of other ethnic groups, they identified the Vietnamese as being the same as themselves. If you look at them they do bear some resemblance, and look more like them than they do their classical negro neighbors. It makes me think that both very dark and very light humans are the offshoots. The skull shape and other mongoloid traits are a different matter though.
I've read 2-3 books on them myself. They are the ancient people of Africa but, their myths would place their origins somewhere around the Mediterranean. I've read (somewhere?) that one anthropologist speculates that they are the leprachauns(sp) of Irish legend. They do have pointy ears, are reclusive and dance around fires all night, lol.
Whether or not the mtDNA represents the only true human woman (with some leakage from the males) alive or simply the tiny minority of women whose genes survive to the present day is purely a matter of faith. How can we ever know which is the case?
I am more concerned that they get the dates right. There is a lot of pressure to keep dates old enough so that they seem "respectable" to the evos. What is instead of "the first (surviving?") woman " being around 150 years ago it was only 50,000? The article assumes the Quazfeh finds are modern humans, but they don't look modern to me, and there is no way to check them by DNA analysis.
The whole dating thing is based on mutation rates. How do we know mutation rates today have been constant for the last 150,000 years? The Vela Super Nova sent cosmic rays at highly elevated levels about 30,000 years ago. That should have raised mutation rates for many thousands of years. If the male DNA can enter the mitochondria, wouldn
't that cause more "changes" than the chance mutation rate? The more changes it has, the older they assume it is.
An Origin of New World Agriculture In Coastal Ecuador (12,000 BP)
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