Twins question and skin color question

[The Raven]

Hello, I have some question I want to ask.

1) Let's say there identical twins marry identical twins, and they have baby's would the baby's of the two families share the same DNA as if they were brothers?

If someone didn't understand I mean: male and female which have identical brother or sister give birth to a baby, and their brother and sister also produce an offspring, will those two offspring’s have the DNA closeness of brothers or sisters?

Skin Color

From what I understand is that when the homo sapien migrated from Africa to Europe he had no need for high melanin level. (I am almost sure this is not true). So basically the question is let's say a group of people (2000) With black skin color come to a country such as Norway and not be mixing with the general population, will after a couple of hundreds of years their offspring’s have very lighter skin color?

If I am wrong then, how come there are many different skin colors in the world?

 

[Moonbear]

Hello, I have some question I want to ask.

1) Let's say there identical twins marry identical twins, and they have baby's would the baby's of the two families share the same DNA as if they were brothers?

If someone didn't understand I mean: male and female which have identical brother or sister give birth to a baby, and their brother and sister also produce an offspring, will those two offspring’s have the DNA closeness of brothers or sisters?

Yes, they would be as similar as one would expect siblings to be, which is not to say they have the identical DNA, but they would share some.

Skin Color

From what I understand is that when the homo sapien migrated from Africa to Europe he had no need for high melanin level. (I am almost sure this is not true). So basically the question is let's say a group of people (2000) With black skin color come to a country such as Norway and not be mixing with the general population, will after a couple of hundreds of years their offspring’s have very lighter skin color?

If I am wrong then, how come there are many different skin colors in the world?

Evolution doesn't happen by intent, so there's no guarantee the same thing would ever happen again...putting an organism into a new climate doesn't cause them to mutate; spontaneously occurring mutations allow them to migrate into new climates. Does that distinction make sense? It's one of the more commonly misunderstood things about evolution.

Also, in the modern world, there's no selection against particular skin colors. Someone with pale skin can slather on sunscreen and survive fine in an equatorial or desert climate. Someone adapted to the heat can wear additional layers of clothing outdoors, and turn on the heat indoors, and survive just fine. Modernization has made those regional adaptations irrelevant.

 

[nipwoni]

Still, it's likely that the skin color of people in that group would grow lighter over time (through natural selection), since this is what has happened to many different human groups when they moved to colder or less sunny climates. It would probably take a lot longer that a few hundred years to make a significant difference, though.

I think there probably is still selection on skin color now. First of all, not all societies are as modern as our own. Even when people have access to sunscreen they often don't use it. Light skinned people in sunny climates do have higher rates of skin cancer. This will probably become even more important in the future because of the damage to the ozone layer. Also, one reason for having light skin in cold climates is for vitamin D formation. In places with less sun, it's better to have lighter skin so more UV rays can get through to form vitamin D. Yes, vitamin D can be added to food, but dark skinned people in cold climates still often don't get enough. Rickets caused by vitamin D deficiency is increasingly common in black children living in cold climates.
http://www.boston.com/news/globe/he...sheds_light_on_how_racial_disparities_happen/