The Babe of the week is none other than, ShiRika Gal Power!!
Hunk of the week
The Hunk of the week is none other than, pravin vinz Power!!
Why is ur skin so dark huh??..
Next time people ask you, "Why is ur skin so dark?" and start laughing their silly heads off, dun lose your cool as there is no reason to. Juz stump them with a well-researched lecture on the history of skin colour and they might just curl their tails in between the legs and listen you out…
Are you aware that if your hide is loaded with lots of a chemical called melanin, your skin is dark in colour? Sunlight stimulates the production of more melanin, thus making your skin darker. But exactly how did we end up with the situation that the people with the lighter skin bunker down near the poles, and the people with darker skin hang out near the Equator? Anthropologists say that its all to do with vitamins.Here's one theory...
Let's assume that our earliest ancestors had a light skin, like our closest relatives the chimpanzees. They evolved some 2 to 4.5 million years ago, in the rain forests of Africa. They were competing for food with a whole bunch of other animals in the rain forests. But out on the open savannas, there were not many competitors.
Now remember that when the Theory of Evolution talks about Survival of the Fittest, it doesn't mean the animal with the biggest muscles - it means the ones with the most children. But too much sunlight can actually interfere with baby-making. It's all because of a very important chemical called Folate, that is very important for making babies. Just one hour of bright sunlight can drop the folate level in a white-skinned person by 50%. Without enough Folate, babies can be born with abnormalities like Neural Tube Defect.
So, out on the sun-drenched African savannas, there was natural selection for people who had darker skin, which would stop the sunlight from destroying the folate. But what about people who live far from the Equator where the sun is very weak? It turns out that these people actually need a very light skin, that will allow as much sunlight as possible to penetrate.
How did skin coloration evolve as our ancestors radiated out from Africa to inhabit other continents? The history of our own species, Homo sapiens, in terms of skin is a fascinating history.If we look at our earliest Homo sapiens ancestors (about 100 to 150 thousand years ago in eastern Africa), we can reconstruct that those ancestors would have had dark skin to protect themselves from the deleterious effects of ultraviolet light. But those populations began to move out of the tropics and colonize areas that were much less intense in terms of ultraviolet light. As they first moved into the Circum Mediterranean, Western Asia, then onward into Eastern Asia, Europe, Southeast Asia, Australia and so forth, these populations would have to undergo some depigmentation in order for them to be able to synthesize enough Vitamin D in their skin. Humans have a light skin colour so their body can make vitamin D. Vitamin D is necessary for proper metabolism of calcium. People with a darkish skin need between two and six times as much ultraviolet light, as compared to light-coloured people, to make the same amount of vitamin D3.
Imagine, for instance, the populations that went from East Africa and slowly made their way into central Asia or northern Asia. These populations would have had to undergo quite extensive depigmentation in order to maintain enough Vitamin D synthesis potential in their skin. But imagine some of these populations that were eventually on their way into Southern India, or what is now Sri Lanka. Those populations that also originated, ultimately, in eastern Africa would have undergone some depigmentation as they moved out of the most intense UV of the tropics, and then they would have undergone repigmentation as they moved down, back into the intense ultraviolet regimes of southern India and Sri Lanka.
This same pattern of intense pigmentation to start out with, followed by a period of depigmentation perhaps 10, 20, or 30 thousand years long, followed again by another period of repigmentation, has been followed by many different populations as they have gone from one part of the world to another. It's not a deterministic process; it's simply an adaptive process as these populations have changed from one area with one particular ultraviolet light regime to another.
Are we seeing any evidence that skin pigmentation is changing in response to current environmental factors? One of the most interesting changes that we are seeing today, of course, is that people are moving from one part of the world to another. You have lots of very light-skinned European people who are moving into areas where there's a lot of ultraviolet light -- either to the southern United States or people moving from England to northern Australia, for example. And so we're seeing people who are inherently well-adapted to low levels of ultraviolet light moving into areas where there's a lot of ultraviolet light, causing them to suffer tremendously from ultraviolet light damage to their skin.
On the other hand, we have an interesting phenomenon with people who are moving from where ultraviolet light is very intense, such as Africa and India, into regions where it's less intense, such as the United States or the UK. For instance, these days there are a lot of people from the subcontinent of India, including Pakistan, moving into the UK and the United States where there are much lower levels of ultraviolet light than they're used to. It turns out that these people are particularly susceptible to Vitamin D deficiencies of various kinds. Although we don't see human skin changing in response to environmental changes because our time frame is too short to see any evolutionary change, what we are seeing are the dramatic effects of human migrations as people move from areas of the world that they are well-adapted to areas of the world where they are not well-adapted in terms of ultraviolet radiation?
If, for instance, an Indian family moved to the UK and lived there for several generations, at what point would their descendants begin to adapt to the climate? It's hard to say how long this adaptation would take because these days adaptation in any human characteristic is very much mediated by our cultural behavior.Humans do a lot of stuff: They wear clothes, they take shelter, they take vitamin supplements, they do all these things to change the nature of their interface with their physical environment. So it's now almost impossible to predict how long it might take for a human population to adapt to a different ultraviolet light regime because we do so much meddling.
Experts say that, one of the most important findings of their research is that skin color is a highly adaptive feature of the human body. It has changed over thousands of years to reflect environmental conditions. That is a wonderful thing in itself because it means that, basically, the skin is a highly flexible organ. We know this already from other types of physiological studies, but in terms of evolutionary biology it is also very flexible. It can change depending on the environmental conditions, which means that skin color itself is really of no value when we look at evolutionary relationships per se among different human populations. You can have individuals from different populations that share a similar bone structure, for instance, but have a completely different skin color. The two are unrelated. And so we can't use skin color for determining relationships between human groups.
Therefore, here's the spill-the stronger the ultraviolet light, the darker the skin.
So just remember, that in our world of fly-by trans-continental mass migrations, from a vitamin point-of-view, the best place for you under the Sun, is where you're from...
