stevestory
Posts: 13407
Joined: Oct. 2005
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I just finished ch 2. So here's the first installment.
The book makes excellent use of illustrations, right from the beginning, and the preface and introduction lay out the overview of the book in very clear language.
In chapter 1, Carroll introduces the idea of modularity in body construction, repetitious segments, for instance. One interesting thing he mentions is the historical pattern of repitition and then specialization. An animal's ancient ancestors might have had 40 copies of one type of tooth, whereas the decendant has 30 teeth of 5 different types. This sort of thing is so common, it has a name, Williston's Law. As a Panda's Thumb watcher, what I'm reminded of is the process of gene duplication. Introduce some redundancy, and then experiment with the redundant part. Very neat.
In chapter 2 he explores some of the early discoveries about polarity and asymmetry, how organisms are different from front to back, up to down, and in to out. Some bright embryologists spent their careers doing macabre experiments wherein they transplanted embryonic tissue from one place to another, and watched the result. By doing so they discovered some basic rules for how organisms lay the foundations of their body plans. Inducing things like polydactyly and eyespots showed how simple early changes could have large effects down the road. Apparently it was thought by some that these types of changes could lead to almost instant speciation, but this is no longer believed to be true. And it is discussed that embryology was so hard and late to develop, that it played almost no role even in the Modern Synthesis in the 40's, which came as a surprise to me.
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(but they were right) 
