[Richard Kimball]

Thanks for the response. The Wiki gives what I had originally thought. The theory was developed in the 1860's, has been discarded, but still gets brought out, probably because people read it in a book, put it in a new book, etc. Although I'm a creationist, I don't see the discrediting of this hurting evolutionary theory in the least. Nothing of what I understand about evolution demands this process during the pre-birth phase.

[jennyp]

The Wiki gives what I had originally thought. The theory was developed in the 1860's, has been discarded, but still gets brought out, probably because people read it in a book, put it in a new book, etc. Although I'm a creationist, I don't see the discrediting of this hurting evolutionary theory in the least. Nothing of what I understand about evolution demands this process during the pre-birth phase.

You need to re-read these passages from the article:

An early form of the law was devised by the 19th-century Estonian zoologist Karl Ernst von Baer, who observed that embryos resemble the embryos, but not the adults, of other species.

and...

Modern theory

One can explain connections between phylogeny and ontogeny if one assumes that one species changes into another by a sequence of small modifications to its developmental program (specified by the genome). Modifications that affect early steps of this program will usually require modifications in all later steps and are therefore less likely to succeed. Most of the successful changes will thus affect the latest stages of the program, and the program will retain the earlier steps. Occasionally however, a modification of an earlier step in the program does succeed: for this reason a strict correspondence between ontogeny and phylogeny, as expressed in Ernst Haeckel's discredited recapitulation law, fails.

See? Each gene does a specific thing, is triggered by a molecule with a specific shape meeting its promoter region - and also gets turned on or off at a specific point in the organism's development.

So a mutation to a gene could affect any or all of those aspects of it. But an organism that has this new mutation to a gene will be indistinguishable from a comrade at the same age until the new mutation starts making itself felt. Add up all the mutations that distinguish one species from its parent species, and you have individuals in the new species going off on their own developmental pathway at some point in their lives - and tending to create precisely the pattern that von Baer (but not Haeckel!) predicted.

BTW, this book, Endless Forms Most Beautiful, is supposed to be an excellent book on the subject of evo-devo - the hot subfield that real, live evolutionary biologists of today work in, studying embryos. (I haven't read it yet, but it got great reviews.)