Some of it is too much to ask of natural selection. Natural selection is
the premise that, given variation and selective pressure, the variants that
better deal with the pressure will be selected for. It does not explain
why there is variation in the first place, except possibly in the case of
selection that favors variation. The origin of new features is a question
for molecular and developmental biology, though there is not yet much
effort being put into the evolutionary aspects of those fields.
David C.