My belief is that Natural (and sexual) selection can not explain all the diversity and all the different levels of evolution. Also NS/SS are very slow taking hundreds or thousands of generations to have a real effect and it seems (to my non-expert eyes) that there were times when species exploding at a very fast rate i.e Cambrian Era. So there must be other mechanisms at work.
We know that NS/SS don't need that long a time to create new features. The Cambrian explosion is an explosion in a very slow moving sense. The explosion takes place over millions of years (5 being the lowest estimate and 40 being a credible estimate). We've seen plenty of evolutionary changes in existing animals over the same 5-40 million year time frame - heck 5m years for example takes us back in time to when the Hominidae are begining to split from other primates...and that is the low end.
Yeah I get the 5-40 million yr time frame but the Cambrian explosion encompasses a move from simple jellies and sponges to vertebrates. We are talking communal one-celled organisms to finned fish and sharks in just 40 million yrs. My point is that other mechanisms MAY be at play besides JUST natural and sexual selection. I AM NOT talking about any fringe or spiritual supernatural stuff but rational ideas like viruses transporting genes between species or organisms incorporating genetic material from consumed prey. Both ideas witnessed and verified in the lab.
For example: species A evolves (thru mutation and NS) photo-sensitive cells giving it a significant edge. A virus infects species A and copies a new virus which includes the gene for photo sensitive cells and then infects species B which is not even in the same family as A and reprograms some of B's DNA to include the photo-sensitive genes. Now Species B has a huge head start w/o NS or SS to develop eyes.
Or multi cellular critter A feeds on single cellular B. B evolves the ability to smell the approach of A and swim away becoming B2. Critter A manages to catch a B2 and instead of digest all material, it can incorporate the genetic material of B2 into its own genome. A few generations later A2 can now smell B2 and zero in on the attack.
Both those examples have been observed, leeches have been found that keep some of the genetic material of their hosts. Viruses have been found to transfer DNA from 1 species to another.
To deny that these observed events didn't happen millennia ago is just silly.