"The Tangled Tree" is a book about how our understanding of evolution has been changing during the years since Darwin publication of the "On the Origin of the Species." Thus, I guess this book should be read as an epic voyage through time (nothing less) by which you can discover the different frameworks that scientist built for putting inside the very meaning of evolution.Yes, all began with a tree. You can see that in a figure drawn by Darwin himself in one of his notebooks (1837). The drawing is accompanied by a note that says, "I think" (p. 8).But as time went by, that tree began to suffer some transformations. New suggestions, and new insights based on new discoveries, opened that tree in several branches and, why not, more trunks. Darwin's drawing presented just one trunk, not three as Carl Woese put it in 1987, only without roots in the ground. There was not a singular and a unique origin.The discovery of the DNA molecule opened more and more possibilities and questions. Nobody was quiet or felt comfortable in the multitude of labs and seminars around the world. There, in the DNA molecule, there was something hidden, and that something (to me the very swerve of the story) was the discovery of the Horizontal Gene Transfer (HGT). In a sentence: HGT meant that the tree wasn't a tree, it was a hedge. There was not only vertical influence (mutations and so on) from parents to sons, but also horizontal influence among species.Genes are not only inherited from ancestors; in fact we receive them from viruses or bacteria that move around us. And this is happening all the time. So, what are we in the end? What are species?David Quammen has made a superb work in this book (390 pages before Notes). He interviewed numerous actors of this adventure movie. Some of them are dead, so Quammen looked for disciples and friends in order to complete his own tangled tree.I don't know what is better in this narrative if the actors or the fascinating story the author tells us (he could have done it without this human element). Hard to say. Quammen is so good a narrator, one of those that go with you all the way through the end. He works for you! You almost not need to think. (Well, almost).Everything in this wonderful exposition of facts, heroes, battles, failures and successes, is intended to be clearly understood. Bottom line: evolution is happening but not as in a tree. Is occurring in parallel, everywhere and all the time. You'll discover by yourself the richness and variety of life as you never saw it. This is new, this is what’s happening today in molecular biology.Now I'm going to read the last book by the same author, "Breathless."And a final note: if you're in doubt with respect to the dissonance that Quammen could have produced within the Darwinian Brotherhood, I would say, don't worry. He has been welcomed by them.That's how science works. Darwin would have been happy.