Kin How We Came to Know Our Microbe Relatives

The problem with many history books is that they are written long after the facts, sometimes when the original protagonists are no longer alive. Historians or journalists often have no choice but to puzzle together the pieces of their story from eyewitness testimony or archival sources. Kin: How We Came to Know Our Microbe Relatives is a welcome exception to this rule. Written by emeritus microbiology professor John L. Ingraham, currently 94 years young, this book gives an intellectual history of the discipline of microbiology based on over seven decades of first-hand involvement and observation.

Kin starts with a short introduction to the older history of microbiology covering the fall from grace of spontaneous generation (see my review of Creatures Born of Mud and Slime) and the rise of germ theory. Ingraham then centres his narrative on the Tree of Life that was drawn up and vigorously defended by American microbiologist Carl Woese and others.

From reading Quammen’s The Tangled Tree I was already familiar with parts of this story. Even so, there are some notable differences between the books. Whereas Quammen started researching his book after Woese passed away, Ingraham has lived through this period and met Woese personally. The Tangled Tree also focuses almost exclusively on the life and career of Woese, at the expense of the other important players in this story. Ingraham’s approach here is far more balanced and wide-ranging.

A second difference is that, being a microbiologist, Ingraham’s story is more technical, going into the details of key experiments and breakthrough findings, rather than the lives of the people involved. Compared to today, many experiments were crude and required clever design as much as astute observation to yield useful information. Even so, Kin is accessibly written, and anyone with even a basic background in biology should easily be able to keep up.

Woese’s discovery of a third domain of life, the single-celled Archaea, was obviously not made in a vacuum. Ingraham recounts how the despair of taxonomists that they could not use shape and structure to tell apart bacterial species led them to look elsewhere. An important figurehead was chemist Linus Pauling who, before DNA’s structure was clarified, suggested that macromolecules such as proteins, DNA, and RNA are information-bearing molecules that could reveal the evolutionary past. This ultimately led researchers to ribosomes, the cellular machinery that turns DNA, using RNA as an intermediary, into proteins, the actual workhorses in a cell (see also my review of Gene Machine). Since all cells, whether from multicellular organisms or bacteria, rely on proteins, the ribosome is old. Very old. Just the thing you need to establish evolutionary relationships. Ingraham covers Woese’s discovery of the Archaea and the bickering before and afterwards over how to organise and name all this diversity.

And then there was the discovery of the structure of DNA (see also Watson’s DNA: The Secret of Life and Unravelling the Double Helix). Researchers initially thought that DNA was too simple a molecule to be the bearer of heritable information. The story of how that was clarified, and how some people received recognition in the form of a Nobel Prize when others did not, is worth reading. It was DNA after all. But how? Watson and Crick’s understated and much-quoted final sentence in their breakthrough Nature paper that “it has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material” proved to be prophetic. But next to this well-known chapter in history, Ingraham also reveals the work led by Marshall Nirenberg that led to the next code-breaking exercise. How does DNA actually code for proteins?

By this point I was half-way through the book and had a nagging feeling. Wasn’t the whole point of Quammen’s The Tangled Tree that this Tree of Life metaphor looks increasingly shaky? I need not have worried. The second half of the book is dedicated to the discovery of the various forms of horizontal gene transfer (the exchange of genetic material within a generation, rather than between parents and offspring). Ingraham poses the very interesting question (the title of Chapter 7): "Can the receiving cell say no?" It is not always in a cell’s best interest to have foreign DNA enter. Next to restriction enzymes (one weapon in a cell’s defensive arsenal), this allows Ingraham to introduce the more recent discovery of CRISPR, which is a sort of bacterial immune system (see also my review of A Crack in Creation). Both have been turned into important molecular biological tools in research. Ingraham concludes that, despite horizontal gene transfer, the Tree of Life metaphor remains useful. One important reason is that ribosomes, still used to define bacterial species, are not exchanged horizontally.

Other topics that are covered are endosymbiosis (see also Symbiogenesis and One Plus One Equals One), the discovery of the microbiome, and the various theories for the origin of life, see The Emergence Life on Earth. Finally, Ingraham instilled in me an understanding and appreciation of metagenomics. One dirty little secret of microbiology is that many bacteria are impossible to grow in the lab. Instead, improved DNA sequencing technology, increased computing power, and enormous databases now allow scientists to simply gather DNA from inhospitable environments to figure out how many microbes there are, without ever actually seeing eye to eye with them.

From the above, you can gather that Ingraham covers a huge number of topics, but he does so without getting lost in irrelevant asides. He provides quite a bit of technical detail, but does so without overwhelming the reader. The result is an intricately structured story that flows very well and shows how all these discoveries interlocked and influenced each other. As I mentioned at the start, it is not often that someone is willing or capable at the end of a long career to sit down and write a cogent eyewitness history of their discipline. That alone makes Kin a noteworthy and admirable achievement.