A rhesus monkey eats watermelon, provided by zookeepers, at the Kamla Nehru Zoological Gardens in India in May 2012. Sam Panthaky/AFP/Getty Images hide caption

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The latest data paint a brighter picture of aging in America. Lisa F. Young/iStockphoto.com hide caption

itoggle caption Lisa F. Young/iStockphoto.com

HIV treatment regimens, like the pills in this patient's hand, keep AIDS at bay, but can take a harsh physical toll over the course of many years. Amy Sancetta/AP hide caption

itoggle caption Amy Sancetta/AP

Bacteroides species are some of the most common bacteria in the human gut. Enviornmental Health Perspectives hide caption

itoggle caption Enviornmental Health Perspectives

An American Cancer Society Relay for Life event at the University of Texas-Dallas in 2006. The events are meant to "celebrate the lives of people who have battled cancer, remember loved ones lost, and fight back against the disease," according to the organization. Josh Berglund/via Wikimedia Commons hide caption

itoggle caption Josh Berglund/via Wikimedia Commons

TimeSlips is a program based on the idea that storytelling can be therapeutic for people with dementia. Dick Blau/TimeSlips hide caption

itoggle caption Dick Blau/TimeSlips