Consider a fantasy species of "natural" time travelers. To define some specifics:
- While it is not effortless, this species can move against the "arrow of time" much as a human can swim upstream a gently flowing river (and they don't need a machine to do so). The swimming metaphor continues: they can "speed up" (or "slow down") the process with effort, to a certain limit. They experience their own subjective time, and age accordingly.
- We have limited multiverse theory: Changes made in the past "fork" into new timelines. These timelines do not exist until created. Not all possibilities actually exist. It is also possible to move laterally from (existing) timeline to (existing) timeline, with some concept of 4D distance between them. To extend the swimming metaphor, they can get out of the water and walk to another stream, which also takes subjective time and effort.
- The species only has one point of real consciousness, or "existence"-- that is to say, they can't interact with their subjectively past selves. If they go back in time, their former double vanishes from the new fork. If they meet with a past version of a friend who is also a member of this species, that friend vanishes in the new fork. Of course, they can sync up if they like.
- Non-members of the species still exist across the timelines at every point, and fork as needed.
- Technically, it's not a single point, but a small "area" of time lasting a few moments, to allow things like seeing a friend moving backwards in time for a short duration before vanishing.
- You can't really save a friend's life except within this tiny little window, because going outside the window will have the friend vanish from your perspective.
These are, in my mind, less relevant to my specific question, but since time travel is such a weird thing when you think about it, I may as well show you how I've hammered out other aspects for my story.
- They can drag a fuzzified amount of matter along with them, such as clothing, held objects, air, etc. They also push on matter in a 4D way. This is like making little eddies in the water, and avoids XKCD "what If: Relatavistic Baseball" effects.
- This doesn't make an infinite number of forked timelines as they go back moment by moment, but will build up effects that influence the new timeline once the person starts going with the flow again.
- Changes to themselves persist. If shot with a gun, going back in time might see the bullet ejecting, but it's not going to heal them from the bullet wound.
- Their location, and forces acting on them at that location, stay intact (unless they're stepping outside the timeline... but they need to step back into a timeline to go backwards instead of laterally). Jump off a cliff and start going back in time mid fall, and you're just going to keep falling as you go back in time. You can see other people and things reversing as you fall, but you keep falling. No "Prince of Persia: Sands of Time" here.
My question is: how could such a species have a meaningful society amongst themselves? Even with the restriction that timelines don't exist until created, it looks like they would have a problem of getting hopelessly separated from each other, eliminating any possibility of civilization. For that matter, it would make finding a mate nigh impossible, and since they aren't immortal that would mean the end of the species.
So how could this work?