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Subtitle: "The New Science of Evo Devo". This cracked up my wife to no end. It's 'branding' for a new movement in biological science, about as hip-sounding as "Extreme Programming". But let's not judge a book by its cover. The author claims that this movement is "Revolution #3", on par with the Darwinian discovery of evolution by natural selection, and Mendel's discovery of genetics. Is it hype? Yes. Is it justified? Maybe...

One thing's for sure: if you like seeing pictures of a lamb born with only one eye (in the center of its forehead), flies with legs where there should be antennae, and x-rays of seven-toed baby humans, this is your book.



The problem with proclaiming revolutions' significance while they are happening, is that by the nature of revolutions they are unpredictable in outcome (see "The Black Swan"). It wasn't obvious to an observer in 1789, or 1848, which one would overthrow a monarchy and which one would fail to. It probably wasn't obvious to peers of Darwin that his ideas would catch on, and Gregor Mendel's peers didn't even really notice his work until after he was dead.

'Evo Devo' stands for 'evolutionary developmental biology'. It's about how genetics makes evolution happen, by changing the way we develop from conception to birth. It's taken as given that evolution by natural selection will reward creatures born with an advantage (not much here for the creationist reader, not even someone to argue with). The question is, how does the mutation process work, exactly?

The question arises because, in the last twenty years, we've found out that a lot of our genes code for multiple things. The same gene which codes for our arms can code for wings in fruit flies, for example. How can one gene do that? Equally complicated is that the same gene does multiple things in the same species. But if one gene is used in limb development and, say, rib development, how can a mutation ever be beneficial? Even if it is useful in one case (longer legs, for instance), if it also causes other body parts to be out of whack, it's almost certain to be a net loss. How can natural selection work?

The answer seems to be that our genes are turned on and off in different parts of the body, and at different times in our development, by switches. These switches (which are coded for in our DNA, of course) can mutate, and only affect one feature. This allows human and chimpanzee to share over 98% of our DNA, while still being quite different. More impressively, we share over 50% of our DNA with mice, who most of us do not resemble nearly so much. If most of this DNA can be use to different purposes by switching it on and off at different times in our development, these numbers are easier to understand.

Also, by monkeying around with the very early embryos of fruit flies, we can get some truly B-horror-movie-worthy pictures. When nature does the same sort of thing, we can get a picture of a lamb head that will take a while to get out of your memory.

Evo Devo, besides being a silly name, makes for a good read. For too long, popular science books on biology have been stuck on the "here's why creationists are wrong" level. I enjoyed being given a layman's view of the mechanisms that evolution can use to actually tinker around with things, from an author who respected my intelligence enough not to waste his breath on trying to convince me of evolution in the first place. He hops from how science actually happens (who discovered what, when, and why it turned out differently than they expected), to how evolution happens, to salient examples from the natural world (e.g. how zebras stripes form). This is the first book from Sean Carroll that I have read, but I hope it will not be the last.