In the mid-1970s, scientists began using DNA sequences to reexamine the history of all life. Perhaps the most startling discovery to come out of this new field--the study of life's diversity and relatedness at the molecular level--is horizontal gene transfer (HGT), or the movement of genes across species lines. It turns out that HGT has been widespread and important; we now know that roughly eight percent of the human genome arrived sideways by viral infection--a type of HGT.

In The Tangled Tree, "the grandest tale in biology....David Quammen presents the science--and the scientists involved--with patience, candor, and flair" (Nature). We learn about the major players, such as Carl Woese, the most important little-known biologist of the twentieth century; Lynn Margulis, the notorious maverick whose wild ideas about "mosaic" creatures proved to be true; and Tsutomu Wantanabe, who discovered that the scourge of antibiotic-resistant bacteria is a direct result of horizontal gene transfer, bringing the deep study of genome histories to bear on a global crisis in public health.

"David Quammen proves to be an immensely well-informed guide to a complex story" (The Wall Street Journal). In The Tangled Tree, he explains how molecular studies of evolution have brought startling recognitions about the tangled tree of life--including where we humans fit upon it. Thanks to new technologies, we now have the ability to alter even our genetic composition--through sideways insertions, as nature has long been doing. "The Tangled Tree is a source of wonder....Quammen has written a deep and daring intellectual adventure" (The Boston Globe).