"In the mid-1970s, scientists began using DNA sequences to reexamine the history of all life. Perhaps the most startling discovery to come out of this new fieldthe study of lifes diversity and relatedness at the molecular levelis horizontal gene transfer (HGT), or the movement of genes across species lines. It turns out that HGT has been widespread and important. For instance, we now know that roughly eight percent of the human genome arrived not through traditional inheritance from directly ancestral forms, but sideways by viral infectiona type of HGT. In The Tangled Tree David Quammen, zone of that rare breed of science journalists who blends exploration with a talent for synthesis and storytellingy (Nature), chronicles these discoveries through the lives of the researchers who made themsuch as Carl Woese, the most important little-known biologist of the twentieth century; Lynn Margulis, the notorious maverick whose wild ideas about zmosaicy creatures proved to be true; and Tsutomu Wantanabe, who discovered that the scourge of antibiotic-resistant bacteria is a direct result of horizontal gene transfer, bringing the deep study of genome histories to bear on a global crisis in public health. zQuammen is no ordinary writer. He is simply astonishing, one of that rare class of writer gifted with verve, ingenuity, humor, guts, and great hearty (Elle). Now, in The Tangled Tree, he explains how molecular studies of evolution have brought startling recognitions about the tangled tree of lifeincluding where we humans fit upon it. Thanks to new technologies such as CRISPR, we now have the ability to alter even our genetic compositionthrough sideways insertions, as nature has long been doing. The Tangled Tree is a brilliant guide to our transformed understanding of evolution, of lifes history, and of our own human nature." -- Publisher annotation.
The book begins with a background to genetic theory, up to and beyond Darwin and Wallace. But the author's primary emphasis is on two discoveries in the latter part of the 20th century that have turned traditional Darwinism on its head. One was the discovery by Carl Woese that there is a third major kingdom of life: that is, not just life without cellular nuclei (bacteria) and life with nuclei (everything else), but a third type of life that has characteristics of both. He named these one-celled creatures archaea, and many are found in extreme environments such as heat vents in the deepest parts of the oceans. The second major finding was that genes can move horizontally between living things, and between creatures in different kingdoms. This was a shocking idea: that, say, fungi DNA could find its way into a mammal's genetic code and be inheritable. And this kind of transfer (horizontal gene transfer) happened not only in the distant past but occurs today. This discovery began a massive effort to understand exactly how genetic changes have occurred over the several billion years of life on Earth and what the effect has been and will be for humans. Think about this: the number antibiotic-resistant bacteria is multiplying rapidly because of horizontal gene transfer. MRSA has been one result. So has the transfer from poultry to farm workers of antibiotic-resistant bacteria: bacteria that took one week to develop immunity in chickens and only a couple of months to horizontally transfer to the humans who work with the chickens.
It was also proven that various parts of Eukaryota cells (those with nuclei) were originally captured bacteria (cells without nuclei) that had survived and been retained as useful - well, if they didn't kill the host cell. This includes the mitochondria, an important organelle in our cells. And chloroplasts in plants. To put it very simply, our genetic structure is composed partially of DNA that moved in from bacteria and other creatures over millions of years: horizontal DNA transfer rather than vertical (passed down from parents and earlier forms in the human lineage).
I was blown away by these findings, most of which are accepted science now and being used as the basis for even deeper research. The next step, at least in the history of genetics, is to contemplate, as Woese did in his final years (d. 2012), where the three (or two, or five, depending on the scientist) kingdoms came from. What structure preceded them, and will we be able to tease out which kingdom came first? Did eukaryotic cells (including us) descend from archaea, a theory recently proposed? After the contemplation comes the experimentation, and I gather this is a major focus for many in the field today: that early morass of non-cellular "life" that gave birth to all else: what was it and how do we identify it?
Some have used the new genetic findings to discount Darwinism and to try to strengthen an intelligent design argument. The author addresses this, pointing out that what's really happening is that Darwinism has not been disproven but has now become only a part of the story, much like Newtonian physics: still useful but not a very deep explanation of what's happening. Oh, and this will disturb that last group: we now know that our cells contain DNA from both chimpanzees and Neanderthals (from matings, not from evolution of any type).
This is wonderful science writing: a very difficult subject made comprehensible and interesting to non-scientists. Very, very highly recommended.
The scientific content would fit on two pages. I've thrown it away.
This is a book containing a tremendous amount of biological information, mostly about the history of life, and it can teach you a lot of things that you didn't learn in high school biology -- in particular, about horizontal gene transfer and about the Archaea, one of the great domains of life whose existence was not suspected until quite recently. Yet this is all mixed up with the life of Carl Woese, the great scientist who recognized the Archaea but who otherwise was rather far removed from the mainstream -- and from all the other research covered in this book.
All of that results in a book that doesn't really lead anywhere. For example, a big part of the theme of this book is that the "Tree of Life" -- the great branching organization that starts with some ancient life form and eventually splits into us and into giraffes and and tree frogs and amoebae and Clostridioides difficile bacteria -- isn't really a tree, because of horizontal gene transfer. If one bacterium can snitch a gene from another bacterium, or if we can "catch" a gene from a retrovirus, then our genetic lineage isn't really independent of that other lineage, right?
Granting that I am not a theoretical biologist, I don't think this follows. The essence of Neo-Darwinism is that evolution proceeds through natural (or sexual) selection based on genetic mutation -- new genes appearing in the genome.
And what, pray tell, is horizontal gene transfer except new genes appearing in the genome? From the standpoint of your cells, it doesn't matter if the new gene came in via transfer or via a radiation-caused mutation. It's just a new gene, and will be selected for or against just like any other new gene. Does this change the tree of life? Not really. If you transfer one or two new genes into me, I'll be a human with one or two new genes, not a chimpanzee or a sea slug. If I were to breed, I would have to breed with other humans or not at all. Does the tree of life have a lot of odd connections between branches? Sure, especially among the bacteria and archaea. But the general picture is still one of diffusion.
So what, exactly, does this book prove? I'm not sure. I'm glad I read it; there really is a tremendous amount of information here. But it doesn't lead to anything. What does horizontal gene transfer imply, apart from the fact that the tree of life is more complicated than we thought? Uh.... What does Carl Woese's life tell us, other than that being cranky all the time doesn't help your chances of having your greatness recognized? Uh.... In other words, what does all this stuff mean? Of course, science probably doesn't have the answers yet. But this book doesn't even give us a clue what questions we should be asking. The real lesson of modern biology is that evolution has no direction and no purpose -- it isn't "intended" to produce humans (or nematodes, or E. coli); it just works to suit whatever creatures are around to their environment. In its lack of a clear purpose, this book may teach us more about evolution than its author intended.
From the science perspective the most important part of this book for the lay reader (and this is popular history, not a textbook) is the discovery and implications of horizontal gene transfer or, more to the point, evolution via infection. The biggest implication being the realization that what look like discrete organisms making up species are at a basic level mobile ecologies; and there are still discoveries to be made that will probably render much of the science considered in this book obsolete.
As for the more negative reviews of this book I don't know what these readers were expecting; this is not a textbook and the usual reader of popular science expects to learn something about the people conducting the science. I also highly doubt that most readers are aware of the state of the science that Quammen is reporting on. I will agree that Quammen is a little too cute for his own good sometimes in his writing style.