For a theory whose empirical strength is so great that it cannot be doubted, universal common descent certainly is doubted a lot.
Prochlorococcus, which lives in the ocean, may be the most abundant species of life on earth. It produces about 20 percent of the oxygen we breathe.
The secret is to restrict one’s explanations for life to unguided natural events. Once that decision has been made, everything else flows deductively from it.