This is an argument from incredulity. Because
one does
not understand how butterfly metamorphosis evolved does not mean it is
too complex to have evolved.
Growth patterns intermediate to full metamorphosis already exist,
ranging from growth with no metamorphosis (such as with silverfish) to
partial metamorphosis (as with true bugs and mayflies) complete
metamorphosis with relatively little change in form (as with rove
beetles), and the metamorphosis seen in butterflies. It is surely
possible that similar intermediate stages could have developed over
time to produce butterfly metamorphosis from an ancestor without
metamorphosis. In fact, an explanation exists for the evolution of
metamorphosis based largely on changes in the endocrinology of
development (Truman and Riddiford 1999).
References:
Truman, J. W. and L. M. Riddiford, 1999. The origins of insect
metamorphosis. Nature 401: 447-452.
