What if the tree of life is not a tree? Nonpareil science writer David Quammen-"the best natural history writer currently working" (The Wall Street Journal)-explains how recent discoveries in molecular biology have changed our understanding of evolution and life's history, with powerful implications for human health. In the mid-1970s, scientists began using DNA sequences to reexamine the history of life. Perhaps the most startling discovery to come out of this new field is horizontal gene transfer (HGT), or the movement of genes across species lines. We now know, for example, that roughly 8 percent of the human genome arrived not through traditional inheritance from directly ancestral forms, but sideways by viral infection-a type of HGT. In The Tangled Tree David Quammen chronicles these discoveries through the lives of the researchers who made them and describes how new technologies such as CRISPR give us the ability to alter our genetic composition through sideways insertions-as nature has long been doing. The Tangled Tree transforms our understanding of evolution, of life's history, and even of our own human nature. Book jacket.