I've been reading a few posts lately asking why, given the numerous time travel technologies Lister and co have found across their adventures, Lister doesn't just use one of them to return to his own time. Many people accuse Doug of failing to address this in the majority of the episodes that feature the crew turning up on some version of Earth's past. I'm surprised that many people appear to have missed the fairly concrete explanation that Lister gives when talking to his infant self in S7's 'Ouroboros'. "For a long time, you'll think that you were abandoned, but you weren't, man. You were put here to create a paradox, an unbreakable circle. With us going 'round and 'round in time, the human race can never become extinct. We're like... a kind of 'holding pattern'." This speech, made only in private, for me pretty much confirms Lister's realisation that he has a duty to his species to ensure humanity's survival in his own time and confirms the incredible sacrifice he is prepared to give in order to remain 'The last human' and give hope for the propagation of his species in a future where mankind would otherwise be extinct. It's the kind of wonderfully idealistic and noble Lister premise that I'm surprised hasn't been more widely discussed or understood. He can never make the selfish decision to go back to live in the past because that would deny humanity any future in the present. It also gives added gravitas to his search for Kochanski, which is not just the rekindling of an old love to him but something important to the very survival of humanity. As absurd as his 'plan' once sounded in series 1, it has become a blueprint not just for Lister, but for the future of humanity. He could return 'home' tomorrow but to do so would essentially be to cause the extinction of the human race in the future he now inhabits.