Darwin's theory which indeed does not address abiogenesis v. biogenesis, is a continuum (evolutionary tree of life) based on the presumption that "life comes from life" (omne vivum ex vivo) which also happens to be the law of Biogenesis.
A description of a chain reaction is not an automatic implication that said reaction has always existed, or that some component of the reaction could only come from another component. Chain reactions can and do have a beginning; The ToE can and does explain the "speciation" reaction without addressing what started it.