The Tangled Tree: A Radical New History of Life

"Quammen is one of the great science journalists, and this is a monument of a book—a masterful retelling of how the ‘tree of life’ was recast in the twentieth century by a band of original thinkers. The tree, a model used to explore relationships between all organisms through time, was famously codified by Darwin in an 1837 sketch (Quammen dubs it a “thunderous assertion”). Among the scientists whose trajectories he follows were Lynn Margulis and Tsutomu Wantanabe, but the spotlight is on Carl Woese, the microbiologist whose research unearthed a new branch of life. Quammen manages to integrate leaps in understanding around this discovery with the plod of the research that triggered them. He wonderfully explicates what I think of as ‘linear collaboration’—that shoulders-of-giants element of science in which successive researchers essentially work together over time, as in a relay race. This is as much a book on molecular phylogenetics, the technique effectively used to redraw the tree, which involves looking at units (nucleotide bases and amino acids) in some long molecules—DNA and RNA, for example. The starting gun here, Quammen reveals, was an idea flung out by Francis Crick that amino acid sequences or chains might reveal evidence for evolutionary trees. After work by others, including Linus Pauling, Woese took up the thread. In the 1960s and 1970s, he came up with profound insights around ribosomal RNA. Some of the most ancient genes code for this molecule, so he saw it as the optimal “fossil record.” But which ribosomal molecule? In a stroke of genius, Woese pinned down 16S rRNA —a component of bacteria—and its variant. Extracting and sequencing ribosomal RNA was a herculean task in the 1970s—beyond clunky. Thousands of pieces of film had to be studied. Lab conditions were ridiculously risky, with scant regard for safety around, say, the radioactive phosphorus used in bacterial culture. But Woese, his postdoc George Fox and the rest of his team eventuall punched through. After years of precise, laborious work, Woese identified Archaea, the single-celled microorganisms that constitute the ‘third branch’ (bacteria and eukaryotes are the other two). The series of papers published by Woese, Fox and others in 1977 are seen by some as the most significant in the history of microbiology. Perhaps inevitably, doubt and dismissal followed. There are more aspects to this many-pronged narrative: endosymbiosis, horizontal gene transfer. There are subtleties and complexities (not least in Woese himself.) This brilliant, un-flashy scientist never won a Nobel and, Quammen asserts, was embittered by that. But he played a vital role in redrawing the tree."