RNA world is still a hypothesis, and self-replication is a doubtful requirement.
In addition, as we know more about cell biology, we are finding FEWER links between the kingdoms.
Not even remotely close. Every stinkin' one of us critters share fundamental chemical and morphologic identities. We all use the transcriptase-ribosomes-tRNA chain to build and repair, we all procreate thru the machinery of miosis and mitosis. All of us have protoplasm inside phospholipid bags that bear a remarkable similarity of composition. Differentiating up the tree a bit, and specializing what I mean by "we", we all have blood flow systems, we all have chemical signaling systems that use the same chemicals to accomplish the same ends, we virtually all have topologically equivalent overall morphological structure, both grossly, and in fine detail, as appropriate to the degree of DNA-mutational clock separation.
Add to that the fact that some species have alternate DNA codings, and the common origin of all life is getting further away as we know more.
This statement draws a blank from me on two scores. 1) Of course all species have "alternate" DNA coding. 2) A single, unicellular origin of DNA life has not been in the cards since about the year 2000, due largely to Carl Woese's work, which changed the official tree of life, at it's root, displacing Kingdoms as the root of the tree. Distinct, DNA-encapsulating unicellularity was not an instantaneous event, by our current lights, so there is no need to develop a scientific explaination for it.
"RNA world is still a hypothesis, and self-replication is a doubtful requirement."
self-replication was the _reason_ for coming up with RNA-world in the first place. It provided the hope of a simple mechanism for RNA transcription, rather than the complicated one we have now.
"Every stinkin' one of us critters share fundamental chemical and morphologic identities."
I did not claim that there were no identities, but that the links are becoming more broken the more we study it.
"This statement draws a blank from me on two scores. 1) Of course all species have "alternate" DNA coding."
Apparently I didn't express myself well enough. There are alternate codings of which DNA sequences map to which amino acids. This would be especially difficult to have happen by neo-Darwinism, as when the code changed, it would change ALL of the expressed enzymes, leaving little chance for survival. There are very few species which have these alternate DNA codings, but they do exist.
"Distinct, DNA-encapsulating unicellularity was not an instantaneous event, by our current lights, so there is no need to develop a scientific explaination for it."
So you come up with an even more unsupported hypothesis in its place? And the root of the tree is not the only place where there are huge, gaping gaps. Turtles and bats come to mind, too.