It's human nature that can be demonstrably mitigated by the instutitions we create for ourselves.
The fact that I can get in a car and drive 3000 miles west, get out in a town I've never heard of till I stumbled across it, walk into a restaurant, be served a burger kindly, and strike up a conversation about any range of common cultural traits, is nothing short of remarkable.
We have created families we call nations. The effect is even more remarkable when abroad - anyone who has been far from home and meets a rare countryman knows the feeling of kinship.
And yet this is artificial and totally contrary to this "human nature" you describe which would dictate that the stranger has nothing in common with us on a biological level.
There is nothing other than our own culture, which has already changed drastically throughout history, and for the better, stopping us from treating every other person in the world in this way. I personally believe that it will probably take a common adversary, organic or abiotic, to truly cement the common bonds of humanity, but I also think it is also possible, though perhaps harder, to achieve this by creating worldwide institutions that affirm our common humanity explicitly and convincingly.
Again, I am not trying to say that local interest is immoral in itself - of course the residents of New Orleans are those most interested by the after effects of Katrina, for instance. They are the ones that live here.
However what is amazing is that people in Alaska undoubtedly know more about that event that happened thousands of miles away in a completely unrelated biome in a very different culture and demographic zone than their own, whereas residents of the Yucatan, much closer and more similar in many respects, were comparatively less affected.
You see the point under this, as I know you have all along of course - nationality is totally arbitrary and meaningless and should be phased out as a moral concern.
This moral fact does not change the reality that it IS a moral concern to many today (the all important normative/descriptive distinction again), but it also does not change the fact that we should be trying to phase it out.
We are, at present, and that is good, but it is up to us to keep ushering it along. It's a collective action thing, and certainly not inevitable.