President Barack Obama speaks to the press in the Briefing Room of the White House April 27, 2011 in Washington, DC. US President Barack Obama released a long form version of his birth certificate after extended criticism by those who do not believe he was born in the United States. (Photo by Brendan Smialowski/Getty Images)

A group of San Bushmen from the Khomani San community practice their hunter-gatherer craft in the Southern Kalahari desert on October 15, 2009 in the Kalahari, South Africa. One of the largest studies of African genetics by an international team from the University of Pennsylvania, published in April 2009, revealed that the San of Southern Africa are the most genetically diverse on earth, and that the San homeland could be the spot where modern humanity began. (Photo by Dan Kitwood/Getty Images)

News personality Katie Couric, left, Jenna Dewan-Tatum, center, and model Chrissy Teigen mingle during the White House Correspondents' Association dinner at the Washington Hilton on Saturday, April 25, 2015, in Washington. (Photo by Evan Vucci/AP Photo)

Revelers take a selfie during a Holi Festival in Madrid, Spain, Sunday, April 26, 2015. The festival is based on the Hindu spring festival Holi, also known as the festival of colours where participants colour each other with dry powder and coloured water. (Photo by Andres Kudacki/AP Photo)

A florist waits for customers at the Piedra Liza flower market in Lima April 29, 2015. The market sells flowers that come from all over Peru. Peru is home to more than 25,000 varieties of flowering plants like geraniums, carnations, roses, hydrangeas and jasmine, according to local media. (Photo by Mariana Bazo/Reuters)

A tea garden worker plucks tea leaves inside Aideobarie Tea Estate in Jorhat in Assam, India, April 21, 2015. Unrest is brewing among Assam's so-called Tea Tribes as changing weather patterns upset the economics of the industry. Scientists say climate change is to blame for uneven rainfall that is cutting yields and lifting costs for tea firms. (Photo by Ahmad Masood/Reuters)

An African immigrant tries to jump a fence into a ferry terminal in the western Greek town of Patras April 28, 2015. Afghan, Iranian and Sudanese immigrants, living precariously in abandoned factories in Patras, southwest Greece, try to stow away on nearby ferries to Italy as they seek a better life in Europe beyond crisis-hit Greece. (Photo by Yannis Behrakis/Reuters)

Framed by the setting sun, an American Bison grazes at the Tallgrass Prairie National Preserve on Tuesday, April 28, 2015, near Strong City, Kan. The buffalo herd at Tallgrass is one of the few herds of wild bison left in the United States. (Photo by Travis Heying/The Wichita Eagle via AP Photo)