When so-called senescent cells were removed from mice, they were healthier and lived longer than mice that still had the cells. Philippe Merle/AFP/Getty Images hide caption

toggle caption Philippe Merle/AFP/Getty Images

Researchers hope Guam's snakes take the bait. Micha Klootwijk/iStockPhoto.com hide caption

toggle caption Micha Klootwijk/iStockPhoto.com

Bob Adams is a lab animal veterinarian at Johns Hopkins University. Maggie Starbard/NPR hide caption

toggle caption Maggie Starbard/NPR

This image shows a human glial cell (green) among normal mouse glial cells (red). The human cell is larger, sends out more fibers and has more connections than do mouse cells. Mice with this type of human cell implanted in their brains perform better on learning and memory tests than do typical mice. Courtesy of Steven Goldman hide caption

toggle caption Courtesy of Steven Goldman