Sentence:  It is likely that the long evolutionary trajectory of "Mycoplasma" went from a reductive autotroph to oxidative heterotroph to a cell-wall–defective degenerate parasite. This evolutionary trajectory assumes the simplicity to complexity <WSD>route</WSD> of biogenesis, a point of view that is not universally accepted. 
Meaning of the word marked with <WSD> tags:  A course or way which is traveled or passed.