Mammoths had a distinctive version of a gene known to play a role in sensing outside temperature, moderating the biology of fat and regulating hair growth. That bit of DNA likely helped mammoths thrive in cold weather, scientists say. Courtesy of Giant Screen Films, 2012 D3D Ice Age, LLC/Penn State University hide caption

itoggle caption Courtesy of Giant Screen Films, 2012 D3D Ice Age, LLC/Penn State University

A Maasai boy and his dog, near the skeleton of an elephant killed by poachers outside of Arusha, Tanzania, in 2013. Jason Straziuso/AP hide caption

itoggle caption Jason Straziuso/AP

Elephant acts at Ringling Bros. and Barnum & Bailey Circus will be phased out by 2018, the circus' parent company said today. The elephants will retire to a conservation center in Polk City, Fla. Tamika Moore/AL.com/Landov hide caption

itoggle caption Tamika Moore/AL.com/Landov

Louis E. Pratt, master ivory cutter for Pratt, Read & Co., shows off eight ivory tusks, April 1, 1955. Courtesy of Deep River Historical Society hide caption

itoggle caption Courtesy of Deep River Historical Society

An elephant in Kenya's Tsavo East National Park, home to some 13,000 of these remarkable animals. Ivan Lieman/AFP/Getty Images hide caption

itoggle caption Ivan Lieman/AFP/Getty Images

An elephant at the Emmen, Netherlands, zoo stands at the edge of a ditch in 2009, a day after another elephant fell into the ditch and died. Olaf Kraak/AFP/Getty Images hide caption

itoggle caption Olaf Kraak/AFP/Getty Images

The arrival of African elephants at a Tucson zoo prompted a call for the zoo's fans to contribute leafy snacks. This file photo shows African elephants at the Pittsburgh Zoo & PPG Aquarium in 2011. Gene J. Puskar/AP hide caption

itoggle caption Gene J. Puskar/AP

A family of elephants in Kenya's Maasai Mara game reserve. Tony Karumba/AFP/Getty Images hide caption

itoggle caption Tony Karumba/AFP/Getty Images