1Sokoljan/Wikimedia Commons, under Creative Commons 3.0
2Science History Images/Alamy Stock Photo
3Cartoon by Jim Morin, copyright © 2012. First published in The Miami Herald on April 13, 2012. Used by permission of Jim Morin.
4Courtesy of Geoffrey M. Hodgson
5Jan Arkesteijn/Rob Mieremet (ANEFO)/Wikimedia Commons, under Creative Commons 3.0
6Illustration by Jennifer Campbell-Smith
7Kichigin/Shutterstock
8Loulouka1/Shutterstock
9Photograph by Greg L. Kohuth, courtesy of Michigan State University
10Courtesy of Antony J. Durston
11Illustration by Jennifer Campbell-Smith
12Kateryna Kon/Shutterstock
13メルビル/Wikimedia Commons, under Creative Commons 4.0
14Paul Inkles/flickr, under Creative Commons 2.0
15Courtesy of Inigo Martincorena, Wellcome Sanger Institute, Genome Research Limited
16Courtesy of William Muir
17Courtesy of William Muir
18National Institute of Allergy and Infectious Diseases
19By permission of Michael Benard
20Courtesy of the Ostrom Workshop/Indiana University
21Jorge Moro/Shutterstock
22Creativa Images/Shutterstock
23Courtesy of Carolyn Wilczynski
24Courtesy of Dennis Embry
25logoboom/Shutterstock
26Erika Cross/Shutterstock
27Courtesy of Alan Honick
28Courtesy of Dr. Kate E. Pickett and Dr. Gerald S. Wilkinson
29Courtesy of Peter Turchin
30Sergey Merzliakov/Shutterstock