The talented science writer David Quammen has a new book out, and it’s excellent. The Tangled Tree explores endosymbiosis and horizontal gene transfer, two aspects of evolution that undercut the traditional ever-more-branching “tree of life” vision for the relatedness of living things. The lineage of organisms is not only divergent, but convergent too: populations diverge and sometimes merge, in whole or in part, complicating the traditional “ramose” structure of phylogenetic trees and evoking a more “reticulate” (net-like, or “tangled”) shape. The reality, revealed by the last 150 years of science (specifically molecular phylogenetics), is that especially for microbes, ‘mergers and acquisitions’ take place regularly, with huge implications for both public health and our understanding of evolution. Specifically, these insights allow us to re-conceive the source of genetic novelty that natural selection can then play with, as well as the actual (past-tense) history of life, including the line of descent that led from microbes to us. This is a history book, a history of the development of ideas, pushed along by interesting scientists who uncover interesting information about the history of organisms. It is a story of people, people who figure things out, who make new knowledge. It’s remarkable in that sense, very much focused on humans going through the process of science, rather than merely the empirical results of their work. These people collaborate and fight, synergize and snipe. I came away from reading it with a much better sense of who Carl Woese was, who Lynn Margulis was, who Ford Doolittle is. These people are essential in the story of how we came to understand who we are as a species, and Quammen is to be commended for his thoughtful, sympathetic rendering of their human essence. He’s a great writer: methodical, erudite, curious, measured. He consciously skips unnecessary information, and lets you know he’s doing it – this editorial sense of efficiency is much appreciated. At the same time, nothing feels rushed. Key notions, the ones that are really worth delving into, really get delved into! The book is written with a gentle redundancy, circling back just frequently enough to remind its readers of key ideas, figures, or data. There’s a lot to keep track of, and I appreciate this “reticulate” structure of the narrative. What’s more, Quammen has a Dan Brown-like talent for ending each chapter with a cliffhanger or teaser that leads directly into the introduction of the subsequent chapter. It’s delicious reading about a fascinating topic. Recommended.