Sentence:  It is likely that the long evolutionary trajectory of "Mycoplasma" went from a reductive autotroph to oxidative heterotroph to a cell-wall–defective <WSD>degenerate</WSD> parasite. This evolutionary trajectory assumes the simplicity to complexity route of biogenesis, a point of view that is not universally accepted. 
Meaning of the word marked with <WSD> tags:  Having deteriorated, degraded or fallen from normal, coherent, balanced and desirable to undesirable and typically abnormal.