We would not expect to directly observe the evolution of new body
parts. Major changes occur gradually over long periods of time.
Finding a new body part one day where there was none the day before, or
even a generation before, would be better evidence for creationism than
for evolution.
What exactly is a new body part? Most evolutionary changes are changes
to existing structures, not additions de novo. We have transitional
sequences showing the evolutionary transition of fins to legs, plus
some understanding of the genetic changes involved (Zimmer 1998,
57-85). Do legs qualify as a new body part?
We also sometimes see duplication of body parts. It is not uncommon
for cats to have extra toes, for example. Should not these qualify as
new body parts?
References:
Zimmer, Carl, 1998. (see below)
Further Reading:
Zimmer, Carl, 1998. At the Water's Edge: fish with fingers, whales with
legs, and how life came ashore but then went back to sea. New York:
Touchstone.
