It will be some time beforewe see Relax, there's nothing wrong with the "slime, protoplasm, &c. "generating transpositionpaper. People aren't a new animal. ButI have long readyforthisyet. Istopped publishing regretted that I truckled to public in refereed journals in 1965 because opinion,andusedthePentateuchal therewas nointerest in themaize term of creation,by which I really controlling elements. meant "appeared" by some wholly Barbara McClintockto Mel Green, unknownprocess. It is mere rubbish, 1969 thinking at presentof theorigin of life; onemight as well think of the originof matter. Charles Darwin to James D. Hooker, March29, 1863 Sometimes my students and others have asked me: "what was ?rst in evo- tion - retroviruses or retrotransposons?" Since HowardTemin proposed that retrovirusesevolvedfromretrotransposons(Temin1980;Teminetal. 1995)the other alternative that retroviruses emerged ?rst and were the predecessors of LTR-retrotransposons has since been a controversial issue (Terzian et al. , this BOOK). While DNA-transposons could not have existed in an ancestral R- world by de?nition, sure enough, some arguments de?nitely point towards apre-DNAworldscenarioinwhichretroelementswerethedirectdescendants of the earliest replicators representing the emergence of life. First, these rep- cators likely catalyzed their own or other's replication cycles via the catalytic properties of RNA molecules. After translation had emerged some replicators possibly encoded an RNA polymerase ?rst. This later evolved into reverse transcriptase(RT),i. e. themostprominentkey-factoratthetransitionintothe DNA world. Simultaneously, replicators could also have encoded membrane protein-genessuchastheenvgeneofrecentDNA-proviruses. Membraneswere likely present muchearlier as prebioticoily ?lms that supported theevolution of a prebiotic-protometabolism (Dyson 1999; Grif?ths 2007).
