Evolution doesn’t select for that, but it’s also important to note that such tendencies are not disselected for, and the value “care about yourself, and others” is simpler than the value “care about yourself, and others except those in other Everett branches”, so we should expect people to generalize “others” as including those in Everett branches, in the same way that they generalize “others” as including those in the far future.
Also, while you cannot meaningfully influence Everett branches which have split off in the past, you can influence Everett branches that will split off some time in the future.
Evolution doesn’t select for that, but it’s also important to note that such tendencies are not disselected for, and the value “care about yourself, and others” is simpler than the value “care about yourself, and others except those in other Everett branches”, so we should expect people to generalize “others” as including those in Everett branches, in the same way that they generalize “others” as including those in the far future.
Also, while you cannot meaningfully influence Everett branches which have split off in the past, you can influence Everett branches that will split off some time in the future.