My WaPo review of David Quammen’s new book on evolutionary trees (and a comparison with other reviews)

I’ve just reviewed David Quammen’s new book, The Tangled Tree: A Radical New History of Life, for the Washington Post. Click on the screenshot to see my review. (Note that the original title, which was a bit misleading, has been changed to the new one below.) It will be in the paper version of Sunday’s Post.

Since the topic of the book is evolutionary trees, in particular their reality (or nonreality, according to Quammen), I asked that my piece be illustrated with Darwin’s famous “tree sketch” from one of his pre-Origin notebooks:

Charles Darwin’s sketch of the “Tree of Life” illustrates his theory that species evolved from a common ancestor. (Photo by Mario Tama/Getty Images)

The point of Quammen’s book is largely that the “tree of life” isn’t treelike, and that’s because of endosymbiosis (e.g., the creation of eukaryotic cells that harbored mitochondria and chloroplasts by ingesting and using other microbes), and, mainly, because of “horizontal gene transfer” (HGT): the movement of DNA between rather unrelated organisms.

Besides this point, Quammen’s protagonist is Carl Woese, who discovered that life really comprises three distinct domains: Archaea, Eubacteria, and Eukarya. Because the book consisted of several distinct stories, I chose to concentrate in my review on what seemed to be Quammen’s main point: that the tree of life is simply “wrong” (his words), and can’t really be represented by a tree. The Tangled Tree falls into the “Darwin was wrong” genre of books.

I disagreed about the unreality of trees, especially in the Eukarya, where assumptions of branching trees have worked well in reconstructing the history of species, despite occasional movement of genes between branches. Even in microbes Quammen isn’t completely correct: while HGT is more common among microbes than eukaryotes, it hasn’t, for instance, completely effaced phylogenetic relationships between bacteria, and of course didn’t prevent Woese from discovering, via DNA sequencing and biochemistry, that Archaea is a separate “domain” from the other two. With a limit of 1200 words, I had to largely ignore the stuff about endosymbiosis and Woese’s discovery to concentrate on the main point of the book: the “hook” that was used to sell it.

You can read my review at the link, or, if you’re paywalled, you can get a copy by judicious inquiry.

I’ll also add one correction to my review. Here’s part of what I wrote:

More remarkably, more-complex species can simply incorporate genes from the environment. Microscopic rotifers, for instance, dehydrate in dry conditions; when they rehydrate, the absorbed water can contain bits of DNA from nearby species, so that the rotifer genome can become riddled with “found” DNA segments from groups like fungi and plants.

The rotifer story now appears to be not at all a case of HGT at all, but of contamination by DNA from other species during sequencing. That was revealed in an article published in Current Biology on August 6, and which I didn’t know about until my article was in press (thanks to Matthew Cobb for pointing that out to me). So even that famous example of HGT is wrong. Some biologists think that most evidence of HGT in eukaryotes is due to contamination of this sort, but I remain open-minded. We already know, as I said, that HGT is not sufficiently frequent in multicellular organisms to efface their evolutionary ancestry.

I want to say a few words about three other reviews that have appeared about Quammen’s book. The first two are at the New York Times (click on screenshots to go to articles):

Seghal is a literary critic, and it shows: she criticizes the book as a piece of writing (she likes it) but doesn’t at all tackle the science. In fact, she admits, if not flaunts, ignorance of the science:

In 1977, Woese and his colleagues at the University of Illinois announced their discovery of a “third domain” of life — single-cell microbes they called archaea — genetically distinct from what were thought to be the only two lineages of life: prokaryotes, which include bacteria, and eukaryotes, which include plants and animals. (It’s O.K., I might have missed the memo, too.)

Missed the memo? If you know the least bit about biology, you know about Archaea. And if you don’t, you shouldn’t be reviewing this book. And there’s this:

But this new knowledge — that we are genetically a mosaic — challenges our conception of human identity. What does it mean to be an “individual,” if we are such composite creatures?

Quammen raises and rushes past these existential questions; like the White Rabbit, he spends some sections in a bit of a mad rush. There’s a “Montana blizzard of facts” he wants to shepherd us through; a dizzying array of scientists, past and present, he must introduce. (Please don’t ask me if I can tell my Norton Zinder from my Oswald Avery.)

This is simple parading of the critic’s ignorance to excuse her inability to discuss the science. It is in fact embarrassing. And she doesn’t grasp the science: there’s not a peep about whether the concept of evolutionary trees are, as Quammen claims, pretty useless.  Seghal’s review is a paradigm for why science books should be reviewed either by scientists or by people who know a fair amount about the science at issue.

Erika Hayden, on the other hand, is qualified to review the book: she’s a science journalist and director of the Science Communication Program at the University of California, Santa Cruz. And her review is better than that of Sehgal, although again she doesn’t weigh the evidence for the existence of evolutionary trees; she takes Quammen’s conclusions at face value.

But Hayden has her own beef: she sees the book as antifeminist:

But if Quammen is writing for the ages, his prose at times risks feeling dated. His book spans nearly three centuries and mentions more than 160 scientists by name. Of those, by my count, only 11 are women, and Quammen often dismisses their scientific credentials and achievements or portrays them as appendages to men in the story.

Lynn Margulis, for instance, fundamentally revised our understanding of eukaryote evolution, elucidating how nature’s most complex cells, including our own, arose when simpler cells joined together. She is the only female scientist who is called out and gets significant space in Quammen’s book. But we hear just as much about her pregnancies, motherhood and marriages as we do about her science.

In contrast, Quammen doesn’t really spend equal time exploring the family arrangements of the male scientists in the book. It’s a classic failure of the Finkbeiner test, formulated by the journalist Christie Aschwanden, which posits that a female scientist’s gender is not her most salient characteristic. If scientists’ family lives are important, journalists should write about the families of both male and female scientists. Otherwise, we perpetuate the stereotype that a woman scientist’s primary responsibility is to care for her family, while men should float free from such pedestrian concerns in their pursuit of research.

As for the imbalance between male and female scientists, that simply reflects the gender composition of the field at the time the work was done. In that sense the book is dated, but not unfair.

I reread those sections, and that on Margulis, to see if Hayden had a point, and concluded that she’s wrong. Margulis’s work was discussed in detail, with her science occupying far more space than a few sentences about her family life, including her marriage to Carl Sagan. (The spouses of male scientists aren’t ignored, either, and I don’t think that the women scientists, who are often praised, are given short shrift.) Quammen’s brief mention of Margulis’s family was meant only to show that she accomplished much of her work when she was a single mother of three children and holding down another job, and was meant to laud her accomplishments during a difficult period of her life. (Margulis, of course, was problematic in other ways, being a 9-11 truther, and someone who pushed her theory of endosymbiosis much farther than she should have. She wrote a book on speciation with her son, for instance, that was so bad that it was the only book I’ve ever refused to review for a major venue. It wasn’t even wrong.) In general, then, I don’t agree with Hayden calling out the book for sexism, but you can draw your own conclusions.

Finally, there’s this review from the New Republic (click on screenshot). Gaffney is identified as “a physician and writer with a focus on health care politics, policy, and history. He is an Instructor in Medicine at Harvard Medical School and a pulmonary and critical care physician at the Cambridge Health Alliance.”

 

Gaffney’s review is good for what it is: a recounting of what the book is about. But it again falls short in evaluating Quammen’s thesis, and says only this (besides a long bit on the transfer of antibiotic resistance among bacteria by HGT):

Ultimately The Tree of Life is merely a metaphor, but I think a pleasant one: It connects us to the lineage of all living things, all the way back to the bag of chemicals—or maybe the single molecule—that one day coalesced in the primordial muck. Yet like all metaphors, the “tree” falls short of reality. For in biology, all boundaries are blurred: between species, sometimes even between individual organisms, and probably between the living and the non-living.

No, not all boundaries are blurred. Homo sapiens doesn’t interbreed with any other species of primate, nor do many, many other species. And really, is the line is blurred between, say, Jerry Coyne and Meryl Streep? How? As for the “unreality” of trees, I disagree. So long as species arise from the transformation of populations, usually geographically isolated ones, the history of life is indeed largely treelike. If it weren’t, we wouldn’t be able to reconstruct the history of life. Yet we can!

Now Quammen’s book has its good points. For one thing, it tells you the nitty-gritty about how science is done, complete with rivalries, jealousies, and backbiting. Quammen did his historical homework. And it’s a well-written story. But as you’ll see from my review, I think his report on the demise of Darwin’s tree is greatly exaggerated.

 

h/t: Stephen