> > There are many unanswered questions about the origin of life which are not
> > mentioned in your textbooks, including:
This statement has two major problems. First, by asserting that the text
fails to mention these unanswered questions, it suggests a conspiracy.
Secondly, there's a good chance that answers for some of these questions
may appear in the textbook if it's up to date. The answers are probably no
more than hypotheses, but they do exist. It would be more accurate to
characterize these as areas of uncertainty with active research going on.
>> Why did the major groups of animals (phyla) appear "suddenly" in the
>>>>fossil record (known as the Cambrian Explosion)?
The increasing number of phyla known from the Precambrian, as well as the
DNA evidence, suggest that this was not nearly as explosive as once (i.e.,
a year or two ago) thought. Many explanations exist for the remaining
diversification, including certain evolutionary innovations, climatic
change, plate tectonic rearrangements, and increasing oxygen levels.
> > Why have no new major groups (phyla) of living things appeared in the
> > fossil record since the Cambrian Explosion?
Bryozoans and various soft-bodied phyla appear later in the fossil record.
Two explanations for the decrease in appearance of new phyla are a decrease
in genetic flexibility and a decrease in number of opportunities for
something novel to evolve.
> > Why do major groups (phyla) of plants and animals have no transitional
> > forms in the fossil record?
If onychophorans are considered a distinct phylum from arthropods, the
armored lobopods and anomalocariids bridge the gap.
If most phyla evolved well back in the Precambrian, we do not yet have any
animal body fossils from this time. Additionally, the earliest
representatives of these phyla may not have been very distinctive
morphologically.
> > How did you and all living things come to possess such a complete and
> > complex set of "instructions" for building a living body?
If such instructions did not exist, neither would you or they. Selective
pressure to have a good set of instructions is very strong. Complex
systems may evolve one step at a time, if the intermediate products are
useful.
These are clearly not definitive, final answers, but they are answers.
David Campbell