A book review in the Oct. 24, 2005 issue of the New Yorker by H. Allen Orr explains a bit about “evo devo” (evolutionary developmental biology), and finally clarifies for me what “ontogeny recapitulates phylogeny” means.
Last things first: the growth of a single organism from embryo to adult may be connected to the growth of a species from the beginning of time (my words, not Orr’s). In his words: “Organisms show two kinds of change through time: during the lifetime of a single animal (you don’t look much like the egg you started as) and during the evolutionary history of a biological lineage (you don’t look much like your three-and-a-half-billion-year-old ancestor).”
The review focuses on Sean Carroll’s book “Endless Forms Most Beautiful”, which supports evo devo, and argues that genes might work like switches. For example, “The same gene, for example, that triggers eye development in fruit flies also triggers eye development in mice. Indeed, genetically engineered flies will happily build eyes if supplied only with the mouse gene. (They build fly eyes, not mouse eyes.)” Wow!!
There's also some cool stuff about modularity looking at stickleback fish as well as an understandable present-day analogy.
Orr reviews a few other books, too, and doesn’t suggest that evo devo is the be all and end all. But it might be an important theory. And Orr explains it in a sophisticated way that non-scientists can understand.
(in our house, evo devo is a cat food, referring to Innova Evo)