The Tangled Tree by David Quammen

The Tangled Tree is a book about the history of molecular phylogenetics, that is the evolutionary development and diversification of species. It is also a book about (perhaps) the most important biologist of the twentieth century, whose name I' ve never heard of. His name was Carl Woese, a white-haired scientist in Urbana, Illinois, who made a discovery in 1977 that changed the way we understand the history of life on the planet.

Until then, scientists believed there were only two fundamental types of organism: Prokarya, made up of organisms, such as bacteria, whose cells do not have a nucleus, and Eykarya, made of organisms, such as plants and animals, whose cells have a nucleus. Woese, discovered there was a third form, the Archaea. His discovery changed the way we see the Tree of Life, the classic Darwinian figure that has been representing the history of life on Earth with a single trunk and a few limbs, branches and divergence representing the lineage and life’s biological diversity.  

The Tree of Life is not a tree anymore. It is a tangled tree, a web. It is not just divergence but also convergence, branches that grow into other branches, from one part of the tree to another part of the tree. It’s what scientists call Horizontal Gene Transfer (HGT), genes that move sideways across species boundaries. Until recently, we knew that genes move vertically, from parent to offspring, species were defined this way. Even in bacteria that reproduce themselves by fission, genes move vertically. Or aren’t they?

Carl Woese and his endless search for truth, triggered a revolution in thinking a radical new history of life, which is the subtitle in David Quammen’s book.  But The Tangled Tree is not a biography. It is about a new method of telling the story of life, from its primordial origins into the fluorescence of diversity and complexity we see now. The method is called molecular phylogenetics, and it means “reading the deep history of life and the patterns of relatedness from a sequence of constituent units in certain long molecules, as those molecules exist today within living creatures. The molecules mainly in question are DNA, RNA, and a few selected proteins. The constituent units are nucleotide bases and amino acids.” The unexpected insights have fundamentally reshaped what we think we know about life’s history and the functional parts of living beings, including ourselves.” We are more complicated than the genes we inherit.

A fascinating and immensely accessible book, from one of my favourite science writers.