Discussion in 'Human Science' started by skaught, Dec 5, 2010.
I second the nomination, Emil..Please Register or Log in to view the hidden image!
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I remember seeing a PBS show some time ago where school kids in Siberia (I think?) were put under bright lights for a given time a few times a week due to lack of sunlight.I assume the lights were some special type huh.
Solar-spectrum fluorescent tubes and twisty-bulbs are available in the USA wherever lights are sold. They're a good idea for anyone who doesn't spend a lot of time in the sun. Home Depot usually puts them on sale a couple of times a year so they don't cost much more than regular fluorescents.
It's not just the Vitamin D, which you can buy in pills at Costco for a few pennies a day--remembering that it's fat soluble so take it with a balanced meal rather than a sugar or starch-and-protein snack. You need about a half-hour per day of sun or artificial sun on your skin. By a mechanism which AFAIK is not completely understood, it recalibrates your circadian rhythm to keep you on a steady 24-hour cycle. Humans have a natural cycle of something like 24 hours and thirteen minutes, and please don't ask me how that evolved. So we need to be reminded that bedtime is now, not thirteen minutes later tonight, 26 minutes later tomorrow night, etc.
And turn the bulbs off a few hours before bedtime, or obviously your body will think it's still daytime and get really confused.
The circadian rhythm is maintained by melatonin, secreted by the pineal gland [and also available OTC in Walgreens]. The levels of the hormone vary during the day and night, being higher during the night as this "hormone of darkness" is secreted in response to absence of light. The biological effects of melatonin are produced by its activation of melatonin receptors.
I used to prefer melatonin during exams and travel when I was too tired or or too stressed to sleep.
This thread is fun, endocrinology is one of my fave subjects Please Register or Log in to view the hidden image!
I didn't think it would even go this far! It's been very interesting! I'm glad everyone is participating!
Rickets is listed as a rare disease by the National Institute of Health, affecting fewer than one in two hundered thousand people. Skin cancer affects more than one hundred people per hundred thousand(http://info.cancerresearchuk.org/cancerstats/types/skin/), and that's in a northern country like the UK. In more tropical climates the rates are even higher:
The effects of sunburn are immediate and severe:
Consider also that rickets is more prevalent in urban areas, where diets are frequently lacking in foods rich in vitamin D. See also darker skinned people such as eskimos who have lived in the far north for thousands of years without 'turning' white. Note also that even though wild animals are covered in a thick layer of fur they still do not get rickets simply because diet is the most important factor as the writer here correctly concludes:
The number of blacks suffering from rickets is tiny and far too insignificant for it to be considered a selection pressure. For your theory to be plausible it would have to be more probable than mine. Yet every single white child needs protecting from the sun, in Africa it would be even more necessary. A white baby left out under the African sun would literally start to cook, yet a black baby would remain unaffected. This is not true of only some white children, but ALL of them.
White skin isn't an advantage within the context we have been debating. Consider:
Clearly, skin cancer is more of a risk threat to whites than rickets and more of a determiner, therefore, in the migration of humans around the world.
The chances of getting skin cancer or sunburn if you are white are significantly higher than those of blacks getting rickets due to lack of sunlight, which remains insignificant at best. The shops filled with sun creams, parasols, hats and a media littered with sage health advice regarding the dangers of the sun are testament to this. Even in northern climates whites are more at a health risk from the environment than blacks.
Therefore Occam's Razor demands the simplest explanation, which is the one I originally presented. Skin color is the cause of the out of Africa migration, not vice versa. Races, therefore, predate the out of Africa migration.
This is the same kind of liberal scientific journalism that encourages blacks to wear sunscreen. It's a product of liberal politics and capitalism, not science.
Finally, rickets exists in Africa. According to your logic ALL Africans should have white skin.
I think you've pointed out the problems yourself.
1. Effects of sunburn are more immediate, hence sunburn has a priority over rickets
2. Skin cancer in Australia The skin cancer is obviously more in people with white skin
3. Rickets is a rare disease. Yes because the amount of vitamin D required to prevent rickets is very low. However preventing the overt, excessive symptoms of deficiency is not the same as providing optimal amounts for health. Nowadays nutrition does not aim at providing just enough nutrients to survive but sufficient nutrition to provide optimum health
Which is why you see greater effects of sunlight on white skin at below the 37th parallel and greater effects of melanin on vitamin D status at above the 37th parallel. Plus we have the boon of fortified foods
Not if the rickets is due to other factors like poor calcium intake.
Just say no, if you like. Most people today are vitamin D deficient in the sense that their serum levels are around the lower end of optimal status - the less time you spend in the sun, the more time you spend in indoor activities, the more you cover up or wear sunblock, the more vitamin D you need from dietary sources or supplements. Even the RDA is abysmally low [400 IU although they've upped it to 600 recently] it should be at the very least 1000 IU. The "normal" status for vitamin D [seum 25 hydroxycholeciferol] is somewhere at 30 or 40 ng/ml depending on whom you ask, but this is what is required to prevent deficiency synptoms. It should be somewhere around 80 ng/ml for optimal status.
Vitamin D deficiency predisposes for multiple chronic diseases and we haven't seen toxicity levels even with levels as high as 10,000 IU so I would suggest at least 1000 IU per day
Contrary to what you may think, most researchers are extremely cautious about making recommendations and all their suggestions usually fall on the lower end of the optimal scale. In the US they even estimate "normal" vitamin D status at 20 ng/ml even though their high incidence of chronic diseases - shows that they need more supplementation!
source for RDA recommendations:http://clinicalendocrinologynewsupdate.org/ArticleDisplay.aspx?id=10073
How does this correlate with the evidence provided in the recent extensive DNA analysis? All non-African populations are descended from a single African tribe, the San or "Bushmen." Although they obviously must have lived in northeastern Africa near Suez 60-50KYA when the two waves of migration took place (Native Australians are descended from the first, all the rest of us from the second), they now live at the southern end of the continent. They have very dark skin, unlike most of us.
This documentary will answer all of your questions. "Journey of Man" The best work done on this subject to date. I'm surprised no one has refrenced this already.
Yeah I saw it once a long time ago. Couldn't remember what it was called. Thanks!
I just want to reinforce re: the title of this thread to point out that some humans variated to a lighter skin tone- we didn't evolve and advance to a higher stage, we simply adapted.
Don't want any haters here.
Jesus. Ok, so I misspoke. I really don't think it's going to be a problem son. Obviously its not so bad. The mods haven't changed the thread title.
I think the answer boils down to this, we started wearing more clothing in response to colder environments which eliminated the need for heavy skin pigmentation. It is interesting to see such a dramatic and quick change in human evolution in response to environmental change. We do evolve. We do change just like any other animal.
Absolutely not true.
Thanks for the link to the Journey Of Man,I ended up watching all 13 videos.Absolutely educational and interesting.To think we could track our Journey out of Africa all the way to America thru our blood/DNA is so cool. I sure did envy the Man making this film.Thanks again.
I'm new here but just wanted to say interesting read.
Also have to say who is this fool Empty sky, who thinks occams razor tells him all white people suddenly decided to migrate north from Africa? So all the "African white people" just upped and moved in the same direction, based on their skin colour? rather than their skin colour being affected by their environment later? that's worth a razor for sure but its not occams.
Thanks for banning this dude.
But that's their hair, not their skin. Humans do the opposite: our hair turns grey or even white as we get older.
Our species originated in Africa, a region with strong sunshine, long before clothes were invented. I think it's reasonable to suppose that the first humans had very dark skin.
Sure. The extremely light-skinned Latvians and the extremely dark-skinned Indians are only separated by three or four thousand years of migration in opposite directions. (The Indo-European people arose on the Pontic Steppe, and spread out to the north, west and south.) The genes that control skin color seem to be rather ephemeral. When a population moves north (in the Bronze Age, when nobody knew about DNA), the people with dark skin start to die from lack of Vitamin D because the melanin in their skin blocks out most of the sunlight--this eventually leaves a population with lighter skin.
Meanwhile their cousins who decided to migrate in the other direction (south) lack the high level of melanin that would protect their skin from sunburn. A large portion of the people with the lightest skin die off from skin cancer, eventually leaving a population with darker skin.
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