In high doses, ultraviolet light can damage skin and DNA molecules, but the body does need some UV light to help us produce vitamin D. Our bodies use melanin to regulate how much UV light our skin lets in.

Courtesy George Chaplin

Ultraviolet Light And Pregnancy

Because women build babies in their wombs, they need more vitamin D to produce extra calcium for the baby’s bones. Could that explain this difference: When scientists look at the underarm skin of men and women in every color group of humans, the women on average are always lighter than the men. Are the ladies lighter to produce a little extra Vitamin D for the babies?

• Listen: Dr. Nina Jablonski describes the “Under Arm” test.

To begin, please point your elbow to the ceiling.

Then imagine yourself naked.

Then look at the patch of skin on the inside of your upper arm, the part of you that almost never sees the sun.

Whatever color you see there is what experts call your basic skin color, according to professor Nina Jablonski, head of the Penn State Department of Anthropology.

And that color, the one you have now, says Jablonski, is very probably not the color your ancient ancestors had — even if you think your family has been the same color for a long, long time.

Different Place, Different Color

Skin has changed color in human lineages much faster than scientists had previously supposed, even without intermarriage, Jablonski says. Recent developments in comparative genomics allow scientists to sample the DNA in modern humans.

By creating genetic “clocks,” scientists can make fairly careful guesses about when particular groups became the color they are today. And with the help of paleontologists and anthropologists, scientists can go further: They can wind the clock back and see what colors these populations were going back tens of thousands of years, says Jablonski.

She says that for many families on the planet, if we look back only 100 or 200 generations (that’s as few as 2,500 years), “almost all of us were in a different place and we had a different color.”

Over the last 50,000 years, populations have gone from dark pigmented to lighter skin, and people have also gone the other way, from light skin back to darker skin, she says.

“People living now in southern parts of India [and Sri Lanka] are extremely darkly pigmented,” Jablonski says. But their great, great ancestors lived much farther north, and when they migrated south, their pigmentation redarkened.

“There has probably been a redarkening of several groups of humans.”

Why We Change Color

The repigmenting process is increasingly well understood.

“Humans started in Africa,” Jablonski says, the part of Africa near the equator where it is intensely sunny with lots of ultraviolet light.

Ultraviolet light, or UV, in high doses can age the skin and damage the DNA molecule, which makes it harder to build a fetus. Not to mention that ultraviolet light can sometimes cause skin cancer.

On the other hand, if a human is plopped down in, say, Norway, where the days can be short and there is precious little ultraviolet light, this creates problems, too. All vertebrate animals need ultraviolet light to help produce vitamin D. Vitamin D helps us absorb calcium from our food to build strong bones. If we don’t get enough ultraviolet light, we’re less likely to survive to reproductive age to produce strong-boned babies.

Thus the dilemma: People who live in sunny climes around the equator have too much UV. People who move away from the equator eventually have too little UV.

Hooray For Melanin

The solution is what Jablonski calls “a really cool molecule”: melanin. In different concentrations, melanin makes skin lighter or darker. Kind of like a Venetian blind, it can let UV light in or keep it out.

Melanin has evolved in many different animals. Humans have had it for a long, long time and what Jablonski and others have learned is that when early humans migrated from the equator, their melanin levels changed.

That doesn’t mean they lost their tans. It means they had very specific genetic changes that allowed them to live and successfully reproduce in less sunny places. Darwin teaches that these changes began randomly. Somebody in the population at some point had a baby, and that baby, just by chance, had a little change in its DNA that made her skin, for example, a little lighter. When that baby moved north to Europe, lighter skin gave her an advantage as a grown-up, because it helped her produce strong-boned babies who could survive and have babies of their own.

Successive mutations created successive generations of lighter and lighter people as they moved north.

“This, in short, really created the gradation of skin color that we see in modern humans today,” says Jablonski. Her map of UV radiation levels on Earth closely mirrors the array of skin colors on Earth.

Skin Color Is A Fleeting Thing

The big surprise is how fast these changes can occur.

“Our original estimates were that [skin color changes] occurred perhaps at a more stately pace,” Jablonski says. But now they’re finding that a population can be one color (light or dark) and 100 generations later — with no intermarriage — be a very different color.

Figuring 25 years per generation (which is generous, since early humans walked naked through the world — clothes slow down the rate), that’s an astonishingly short interval.

It’s “a blink of an eye,” she says.

Audio & More available at NPR (Click Below)

Your Family May Once Have Been A Different Color : NPR.

At 100, NAACP fights to keep struggle alive – Race & ethnicity- msnbc.com.

Scientists are keeping a close eye on orbital debris created when two communications satellites — one American, the other Russian — smashed into each other hundreds of miles above the Earth.

NASA said it will take weeks to determine the full magnitude of the unprecedented crash and whether any other satellites or even the Hubble Space Telescope are threatened.

The collision, which occurred nearly 500 miles over Siberia on Tuesday, was the first high-speed impact between two intact spacecraft, NASA officials said.

“We knew this was going to happen eventually,” said Mark Matney, an orbital debris scientist at Johnson Space Center in Houston.

NASA believes any risk to the international space station and its three astronauts is low. It orbits about 270 miles below the collision course.

ABC News: Scientists Eye Debris After Satellite Collision.

Feb. 12 (Bloomberg) — President Barack Obama paid tribute to his hero, Abraham Lincoln, at a celebration for the reopening of the theater where he was slain.

“Despite all that divided us — North and South, black and white — he had an unyielding belief that we were, at heart, one nation, and one people,” Obama said last night at Ford’s Theatre in Washington. “And because of Abraham Lincoln, and all who carried on his work in the generations since, that is what we remain today.”

Obama, the nation’s first black commander-in-chief, often invokes the name and symbols of the assassinated president who ended slavery and brought the U.S. through the Civil War. Both men rose from the Illinois state legislature to the highest office in the land and both built reputations as skilled political orators.

The reopening of Ford’s Theatre after an 18-month refurbishment coincides with a celebration of the 200th anniversary of Lincoln’s birth. Obama, 47, who took the oath of office on Lincoln’s bible, will travel to Springfield, Illinois, today to mark the bicentennial.

Obama and his wife, Michelle, joined politicians and Ford’s Theatre donors to watch a series of songs, readings and speeches performed by celebrities such as Ben Vereen and Kelsey Grammer.

The theater also unveiled a videotape, to be shown at its museum, in which the four living past-presidents — George W. Bush, Bill Clinton, George H.W. Bush and Jimmy Carter — recited Lincoln’s Gettysburg Address, accompanied by Matthew Brady’s Civil War images.

Empty Presidential Box

The Obamas watched from the front row alongside House Speaker Nancy Pelosi. None of the nation’s leaders have sat in the presidential box since John Wilkes Booth shot Lincoln there during a performance of “Our American Cousin” on the evening of April 14, 1865.

The event was a retrospective of Lincoln’s life, from his humble beginnings described by James Earl Jones’s baritone to Vereen’s impassioned reading of the Emancipation Proclamation without the prompter, which broke mid-show.

The highlight for the audience of about 650 was classical violinist Joshua Bell’s “Variations on Yankee Doodle,” which was by turns playful and mournful.

Broadway singer Cheryl Freeman gave an electrifying rendition of a song from the play “The Civil War,” followed by Audra McDonald, Jessye Norman and Joshua Bell for “The Battle Hymn of the Republic,” which earned a standing ovation.

Host and actor Richard Thomas called the facility the most-famous theater in America, which had morphed from a scene of tragedy into a symbol of Lincoln’s legacy.

Lincoln Medal

The gala event included the presentation of the Lincoln Medal given each year to someone whose work, accomplishments and attributes “exemplify the lasting legacy and mettle of character embodied by the most beloved president in our nation’s history,” Ford’s Theatre said. This year, the recipients were filmmaker George Lucas and actor Sidney Poitier.

In the aftermath of the assassination, the government bought the theater, which dates to 1861, from Ford for $100,000 and gave it to the War Department for use as storage space and an Army Medical Museum.

At one point, the interior collapsed, so now only the exterior walls are original. In the 1960s, the theater was rededicated as a memorial to Lincoln, and the National Park Service used historic photographs and contemporary accounts to reconstruct the box and the theater as it looked that night. Almost a million visitors pass through every year.

Red Upholstery

The theater has just 658 seats, done up in red upholstery. Lincoln’s box sits just above stage left. On the balustrade is one of the few surviving artifacts from that time, an engraving of George Washington.

The renovation was part of a larger $50 million fundraising effort known as the Abraham Lincoln Bicentennial Campaign that’s also supporting the building of a new education center. The campaign benefited from a $5 million donation from Exxon Mobil Corp. and $2.5 million from the State of Qatar, the theater said.

Other donors included AT&T Inc., BP America Inc., General Dynamics Corp., Toyota Motor Corp., AMR Corp.’s American Airlines and Lockheed Martin Corp., according to Ford’s Theatre.

Bloomberg.com: Arts and Culture.