Basically without Crichton there'd be no Farscape.
Crichton is our reference point in the various adventures that the crew of Moya have.Since he is
the only HUMAN in the show his point of view is
always important as to the understanding of the
events of each week's episode.

But, as we found out in the mini-series, Crichton really isn't the only human, is he? Well, kinda sorta, though, since the Eidarans took humans 20-some thousand years ago and turned them into the Peacekeepers, it's more like humans and Sebacians have a common ancestry...

Though, if that is the case, why is it, that only Interions, Jool's race, were actually closer to humans, so that they had the right parts to donate to John? If indeed, Aeryn's and John's anchestors are one and the same, shouldn't she have been able to donate something to John? Ah, heck, what about when Aeryn was dieing, and they needed to get to a Peacekeeper base to get a tissue sample, couldn't John do?