One theory does have plants and animals deriving from the same (theoretical) unicellular life form. Other theories have them deriving from seperate lines.

Whose theory derives them separately? Both are DNA/RNA based: for two separate life- forming processes to come up with the same extremely complex answer WOULD be coincidence on a gale-in-a-scapyard scale.

It is probable that life originated only once, at least on our planet. Though it was probably based on a much simpler chemistry than nucleotide chains.

It would probably please the Christians to know that one candidate is self- replicating structures sometimes found in ....... clay.