I picked up this book a few weeks ago when I was at the 'brar.
I've read a lot of stuff on evolution over the years. I think Dawkins has the position that I most agree with, but his writing is really hard to get through. I've been working on "The Ancestor's Tale" for a few weeks off and on, and while it's easier to read than some of his stuff, it's still really hard work to read. So, I was happy to read something by somebody else.
Carroll works in the field of what is known as "Evo Devo". No, it's not about this, but about how genes and embryology work together to create an animal. As you probably know, all DNA contains genes, which code for proteins. What you may not know is that at the head of every gene - in the region that has sometimes been labelled as "junk DNA" - are a set of receptors that determine whether a specific gene is on or off. Carroll's thesis - which is well supported by examples - is that it is modifications in these switches that are the primary driver for evolution rather than modifications to genes themselves. This explains how humans and chimps can share 98% of the same genes but be so different. We all share similar toolkits, but they're wired up differently.
If you've ever wondered "how do the legs know where to grow?", this is a book for you.