The Tangled Tree

Before Darwin, the phrase “tree of life” conjured the image of an ancient grove in an Edenic location. To most biologists nowadays, and possibly a majority of scientists, the phrase brings up the image of evolutionary relationships from the origins of life to the present age. Before Harry Potter, the word “transfiguration” had something to do with a seemingly magical event of prophetic significance atop a mountain. To anyone who has read the Harry Potter books, it is the magical practice of changing one object into another. I would say that chemistry is about the transformation of one or more molecules into other molecules – it’s transfiguration at the molecular level. That’s the subject of another post. Today we’ll discuss the Tree. Or trees. Or maybe a tangle of bushes. Or a web.

I just finished reading The Tangled Tree by David Quammen. Personally, I think it is one of the best science-related non-fiction books I have read. This probably has much to do with my research interests related to the chemical origins-of-life. My love of history probably factors in somewhat. And Quammen is an excellent writer. He keeps the reader engaged with fascinating vignettes from his interviews with scientists all over the world. But he doesn’t lose sight of the science; and he builds the narrative one piece at a time into a glorious blend. A web perhaps. But that’s actually the point of the book.

The Tree story begins with Charles Darwin. But he didn’t really draw much of a tree. There is a “diagram of divergence” in his famous book, On the Origin of Species, which is wispy in a tree-like way. The famous depictions of “trees of life” in the nineteenth century are probably due to Ernst Haeckel. Much has been written about the life of Darwin, but I haven’t read many exposes of Haeckel, so I was pleased to learn more about him through Quammen’s book. Haeckel “leaned toward botany, but when he reached age eighteen, his father, concerned for the practicalities, pressured him to study medicine.” Sound familiar? That was back in the 1850s. “[Haeckel] hated the medical curriculum but stayed with it, stealing time to read more Humboldt and Goethe amid his studies.” You might say he forged his own liberal arts curriculum! He did however enjoy histology, and he “discovered an aptitude for drawing tiny structures in fine detail, one eye on the microscope eyepiece, the other on the page.” You’ve likely seen Haeckel’s famous illustrations somewhere even if you didn’t know they were his!

While Tangled Tree begins with Darwin, the main character in the book is Carl Woese. Both brilliant and odd, Woese is most famous for discovering the archaea. When I was in school, my biology class only taught us about bacteria/prokaryotes and eukaryotes. The latter have a cell nucleus, while the former do not. I had also learned about the five kingdoms: Monera, Protista, Fungi, Plantae, Animalia. That’s likely thanks to the strong evangelistic abilities of Lynn Margulis, famous for championing endosymbiosis against the disbeliefs of the scientific community back in the day.

Many other famous scientists enter and exit the narrative. I was particularly blown away by the stories of Fred Griffith and Oswald Avery. I had learned about their famous experiments as foregrounding the “discovery” of DNA as the genetic material which then led up to the Watson-Crick breakthrough. What I didn’t know, which Quammen makes very clear, is how important and strange their experiments were in relation to horizontal gene transfer (HGT). While Woese may be the dominant personality in The Tangled Tree, the main story is about HGT.  Quammen aptly subtitled his book “A Radical New History of Life”. Thanks to HGT, possibly very rampant in those origin-of-life early days, there really isn’t a Tree. A tangled web might be the more appropriate image.

The kicker of the story, though, is that HGT still takes place, and not just among bacteria and archaea. Genes are being transferred through “infective” heredity – a much faster evolutionary process than Darwinian heredity, the kind that we learn about in school. If you want to push evolution by leaps and bounds, HGT might be the main mechanism for wholesale significant changes. How do organisms best acquire the necessary adaptations? HGT might actually be the main and most significant driver. Those scary MRSA bacteria you’ve heard about – how did they evolve multiple-resistance so rapidly? And did you know that bacteria were discovered with resistance to modern drugs before those drugs were invented? There’s a nasty fight going on in the microscopic world, and you have to adapt quickly to stay alive.

Quammen closes his story with contemporary examples. For the first time in the history of life, a “higher” organism is able to manipulate wholesale movement and modification of genes. That’s us. Humans! You’ve likely heard about CRISPR – but did you know that the reason those sequences exist are because organisms use them as a defensive mechanism against the invasion of infective heredity? I’ve talked a lot about the prominence of HGT and microorganisms in this post, but Quammen spends a chunk of his book talking about the different humans in the story – their foibles, their successes, their highs and their lows. They defend their intellectual territory and fight for recognition amidst a tangle of knotty scientific questions.

I highly recommend The Tangled Tree. It’s even better than the excellent I Contain Multitudes. And now I feel motivated to play some Bios Genesis, and pay closer attention to HGT abilities on the mutation cards! Here’s a recent example where my amyloid hydrolyzing marine bacteria also has evolved a homeobox with HGT capabilities.