Thursday, September 29, 2005

Books (Science): Endless Forms Most Beautiful

The book I was finishing when I was inspire (if that's the word) to try writing about reading was Sean B. Carroll's Endless Forms Most Beautiful: The New Science of Evo Devo, an introduction to evolutionary developmental biology, or "Evo Devo". Evo Devo is the study of how the development of an individual organism, based on its genetic code, can teach us about the interrelationships between different species and how form can change over generations.

I picked up the book largely because of the review at PK Myers' Pharyngula. Myers' review is a little odd -- he opens it talking about how disappointed he was in the book, but quickly turns positive:

So I read the whole thing with a bit of exasperation, waiting for him to get to the good stuff, and he never did. But then after thinking about it for a while, I realized what the real problem was: he didn't write book for me, the inconsiderate bastard, he wrote it for all those people who maybe haven't taken a single course or read any other books in the subject of developmental biology. I skimmed through it again without my prior biases, and realized that it's actually a darned good survey of basic concepts, and that I'm going to find it very useful

Since I've never taking a course in developmental biology, it sounded like a good fit to me.

This isn't supposed to be a book review site, just a talk-about-the-book-I-read site, so I'm not going to critique it in any detail. It is a good survey of basic concepts, and I enjoyed Carroll's writing a lot.

My main gripe is that Carroll's not quite as novice-ready as Myers suggested. He sometimes assumes more knowledge of biology than a bio-newbie might have. For example, he explains what DNA bases are, and what transcription and translation are, but he doesn't explain how it works -- a review of how the genetic code maps bases onto amino acids to make protiens would have been nice. So far as I remember, the names of the bases only appear in the caption to a diagram.

That's not a big problem -- you don't need to know the details of transcription and translation to follow the rest of the book. A bigger issue comes in the discussions of how genetic switches regulate how (for example) a developing insect embryo becomes divided into segments, some of which eventually develop legs / wings / etc based on their position on the embryo. Carroll explains how (roughly speaking) combinations of switches tell a cell "If you're located 15 degrees forward on the embryo, turn on the leg-developing genes", but I never got a clear notion of just how each cell (in which the genetic switches are being activated or repressed) knows that it is 15 degrees forward on the embryo.

Fortunately, I had read Armand Leroi's Mutants: On Genetic Variety and the Human Body a few months back. Mutants tells how the abnormal development -- such as polydactyly, having extra fingers or toes -- can teach us about the genetics underlying human development. This is essentially the same material as in Endless Forms' second chapter, Monsters, Mutants, and Master Genes, but with different emphasis. Mutants doesn't cover a wide variety of examples of genetic switches, but it does a better job at explaining the embryonic geography question that I felt was glossed over in Endless Forms.

Likewise, one of my favourite science books is Larry Gonick's Cartoon Guide to Genetics, which fills in a lot of the missing information on DNA mechanics -- including a far more detailed explanation of how a lac repressor actually represses. The chapters on DNA in Douglas Hofstadter's Godel Escher Bach are also worth reading as an introduction to the subject.

Anyway, I said this wasn't supposed to be a real review, so that's enough for now. Endless Forms is definitely a good introduction to Evo Devo. A little background in how DNA works makes it better.

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