Guest post by Theodore W. Pietsch When most people think of trees, they envision the leafy-green, growing, photosynthesizing kind, but there’s a vast forest out there made up of an entirely different kind of tree—branching diagrams and related iconography that attempt to reveal the relationships of plants and animals. For at least the past 500 years, naturalists, realizing that words are not nearly enough, have sought to demonstrate similarities and differences (or to reveal the imagined temporal order in which God created life on Earth) among organisms pictorially, that is, through a fascinating array of diagrams of various sorts. Most of the diagrams resemble trees in the botanical sense—images with parts analogous to trunks, limbs, and terminal twigs. [slideshow] I first became interested in these “trees of life” as a young graduate student some 45 years ago and, for no other reason than I thought they were beautiful, I’ve been collecting them ever since—making photocopies and filing them away, with no thought of what I might do with them later on. Then in 2009, when the world was celebrating Charles Darwin’s birthday (1809) and the publication of his On the Origin of Species (1859), I again began to think more about “trees” and it dawned on me that a book about them might be worth pursuing. I dug out my old files and soon realized that my collection hardly did the subject justice. I then began a determined search for more and found, not just more of the same, but a surprising, almost infinite variety of design. And the rest is history: Trees of Life: A Visual History of Evolution was published in April 2012 by the JHU Press. I invite you to take a look and see for yourself these images that attest to the manifest beauty, intrinsic interest, and human ingenuity revealed in trees of life through time. Theodore W. Pietsch is Dorothy T. Gilbert Professor in the School of Aquatic and Fishery Sciences and Curator of Fishes at the Burke Museum of Natural History and Culture at the University of Washington in Seattle. He is author of more than a dozen books, including The Curious Death of Peter Artedi: A Mystery in the History of Science and Oceanic Anglerfishes: Extraordinary Diversity in the Deep Sea.