Dr. Richard Schlegel and postdoctoral fellow Nancy Palechor-Ceron use a microscope to look at human epithelial cells growing on mouse fibroblasts at Georgetown University Medical Center. Lauren Wolkoff/Georgetown University hide caption

itoggle caption Lauren Wolkoff/Georgetown University

Rob Knight, co-founder of the American Gut Project at the University of Colorado in Boulder, works in the lab where the samples are processed. The American Gut Project hide caption

itoggle caption The American Gut Project

Georgetown's Robert Clark says it's very difficult to say precisely how many experiments have been spoiled by contaminated cell lines. Phil Humnicky/Courtesy of Georgetown University hide caption

itoggle caption Phil Humnicky/Courtesy of Georgetown University

Do you want to go to the park? Mango Doucleff, of San Francisco, responds to her favorite command by perking up her ears and tilting her head. Michaeleen Doucleff/NPR hide caption

itoggle caption Michaeleen Doucleff/NPR

A turkey vulture makes quick work of a dead rabbit at Martin Luther King Jr. Regional Shoreline park in Oakland, Calif. Sebastian Kennerknecht/Minden/Corbis hide caption

itoggle caption Sebastian Kennerknecht/Minden/Corbis

Women participate in a breast cancer fund-raising in Denver in 2011. Despite decades of awareness campaigns, the survival rate for women with metastatic breast cancer hasn't improved. Helen H. Richardson/Denver Post/AP hide caption

itoggle caption Helen H. Richardson/Denver Post/AP

Caltech biochemical engineer Frances Arnold was awarded a National Medal of Technology and Innovation by President Obama in 2013. Jason Reed/Reuters/Landov hide caption

itoggle caption Jason Reed/Reuters/Landov

Researcher Svante Pääbo, was able to extract a complete genome from this ancient human leg bone. Bence Viola/Max Planck Institute for Evolutionary Anthropology hide caption

itoggle caption Bence Viola/Max Planck Institute for Evolutionary Anthropology

Isabella Beukes, of Santa Rosa, Calif., has been legally blind for more than 40 years. An experimental treatment derived from embryonic stem cells seems to have enabled her now to see not just color but also some shapes. Tim Hussin for NPR hide caption

itoggle caption Tim Hussin for NPR

Insulin is produced by the green cells that are in clusters about the same size as the islets in the human pancreas. The red cells are producing another metabolic hormone, glucagon, that prevents low blood sugar. Harvard University hide caption

itoggle caption Harvard University