To a casual inspection, this world's biota resembles the Earth/Arda standard, but with a wider slice of evolutionary history than normally exists at one time outside Valinors. The sapient population is in the low thousands, with a stone-age level of technology. The oldest people appear to be middle-aged, mostly much younger, and the sapient inhabitants comprise most of the youngest generations of a larger population of which the older generations are non-sapient hominids.
"It's possible you'll stop evolving if you leave the world, yes. Or it might only be a problem if you have children in another world, or conceive them there - different kinds of world-properties work different ways in terms of how they're passed on to kids. But if some of you want to visit or move to Vanda Nossëo anyway, you can."
"Well, if we might all stop evolving we can't do it."
"It would mean we'd never die and we could get Birds and Sad-About-Everything and so on back. That's worth not evolving for."
"I don't think it's worth not evolving for. That would mean Singer's kids are as stupid as she is and our kids are as stupid as we are and we never find out what comes next in evolution.
"And otherwise everyone dead stays dead, and everyone who's alive now eventually dies too!"
"We'd eventually find out what was next. It would take many, many generations but we'd live for many, many generations. And on the other hand, the other way the dead don't stay dead forever, they stay dead until we can figure out how to use magic ourselves."
"Alright, but our children wouldn't get to be whatever that thing was."
"We also wouldn't need to wait many many generations because not every band is going to join Vanda Nosseo, and we can visit the people who don't.
"Right. And it would be really bad if we stop evolving but our enemies don't."
"It would also really bad if out enemies get Vanda Nosseo's magic and we don't."
"I think eventually being smarter matters more than having stuff invented by people who were smart to start with but won't always be"
"Not if they kill us all before we get there!"
"It sounds like Vanda Nosseo wouldn't let its members do that? Right, Nelen?"
"What if we wait until some people smart enough to understand this plan are too old to have children, and then send just those people to Vanda Nosseo? That way no-one stops evolving and also no-one stays dead forever."
"Vanda Nossëo members are not allowed to kill people," he confirms. "I think it's pretty unlikely that some of you going to another world could lead to all of you stopping evolving, but I can't be sure."
"What if you test how all that works with animals and then we can decide where to go once we know more?"
"Okay. I can tell some people to catch some bugs and take them to another world and see what happens to the ones there and here."
"If we only sent some people to Vanda Nosseo, would you let those people learn magic and use it for the rest of us?"
"Probably! Some of the kinds of magic are harder to get access to than others."
"Mostly we want are the resurrection and the healing and the not ageing. How hard to get access to are those?"
"Most people reverse aging by going to a place where they can shapeshift and shapeshifting younger, but if that doesn't work for you, there is a magic solution we can bring here. There are many kinds of healing; if you want to have it yourselves probably the easiest way would be to get someone over here to teach a class on wizardry, but if you'd be happy to just have someone stationed here who can heal that would be doable with someone who can also do the waking half of resurrection. It's two steps, creating a body for the dead person to live again in and then making it wake up. Also it works on most kinds of people and it might work on you but it's also possible it won't."
"If we might not be able to get resurrected, that makes it more important to get not-ageing and healing sooner rather than later. We can probably still wait to see what happens to the bugs."
"How many people would need to join Vanda Nosseo to pay for healing and resurrection and not-ageing to be available to all of us? Either sort of not-ageing."
"That depends. Healing isn't very expensive. Just a few of you could probably pay a healer to come by here occasionally, even if they didn't want to live here all the time. The anti-aging jewelry is actually really expensive, but you can get it subsidized if you're a member - maybe also if you're not but it'd be a different organization. Resurrection it might depend on whether you need it done here or if it can be done somewhere else. It costs less than the anti-aging jewelry, but still enough that it takes most people a few years to save up to resurrect someone."
"Well, even if people who get resurrected can't have evolved children anymore, that's still better than them being dead."
"Right, but if you have some kind of more complicated dependency on the world, that would interfere with resurrecting locals in other worlds and you'd need to arrange it here. We'll need to check it - not in reality, with a precognition in case something does go wrong."
Once it's clear that no-one has an immediate reply to that, someone will ask
"Evolving fast is a this-world thing. And you said different world-things work differently. What things do other worlds have?"
"Different worlds have different kinds of magic, and different neighbors!" He can show them a map and point out where all the magics they have observed came from. "Some worlds have the same people on them, or some of the same people, and some worlds are almost exactly alike apart from being at different times."
That last part there is confusing.
"What do you mean, the same people? By different times, do you just mean some of them have been more evolved for longer and invented more things?"
"Hm - imagine there were two worlds like this one, exactly alike, with a copy in each world of all of you and every tree in the same place. And then we visit both of them, on the same day; but in one of them, it's this day here, and in the other, it's last week."
"Huh. But they don't have the same neighbors, by the look of it, so they get visited by different people like you at different times?"
"That's right. These worlds," he highlights some Ardas, "are all just about exactly alike except for when they are in their timeline and who visited them and what happened then. This one is a lot like them," Space Arda, "but it's sort of the same story at a different scale - bigger, with some extra people, like Tarwë, who is from there. Every Elf who would have been around in that year in these Ardas is there, but there are also some additional ones, like him, and some other details are different too."
"And Earths have all the same landmasses, and a lot of the same histories, but they all have different magic."
"Bigger scale, like, in other Ardas bands did things and in Tarwë's Arda bands-of-bands like Vanda Nossëo did those things?"
"Mostly the bands are just bigger rather than being more complicated in other ways, but things were - farther apart, mostly."
"What magic do the different Earths have?"
He can list them! That one has magic based on emotions, it can grant wishes. That one has a magical trait some people are born with that lets them cast spells with wands. This one over here has a variant physics rather than a magic but it acts much like a magic in practice, allowing people to turn into animals. That one has vampires and werewolves and witches. This one's got people coming over powerfully magical when the moon does thus and such. This one has some lowkey psychic powers, which are subject to some debate about their magicalness, but the Earthlings mostly don't have them. In this one you can summon beings from these neighboring worlds and those do cool stuff.
"If you can grant wishes, why are some things still expensive for you?"
"I want to turn into a bird!"
"Yeah, hopefully it will be safe for us to travel there."
"Each person only gets one wish, and only one person can grant the wishes, so they all have to be checked for safety and then narrowed down to the most important ones. Plus it only works in that neighborhood, so it doesn't work well for anything that you want to have in another place."