Ehm, those are different species? Are you suggesting that humans are made up of different species?
A state is a three-way bargain between the living, the state, and the unborn. The state imposes all sorts of inconveniences on us---why do we put up with it?
The constitution lists several reasons---common defense, general welfare, and to "secure the Blessings of Liberty to ourselves and our Posterity"
Imagine, privileging one's own children over someone else's! How aggressively family-ist.
In other words, one of the primary purposes of a state is to act as a vehicle for inheritance.
That's why immigration is not a solution---the point of a state isn't "people," it's our children, specifically. Without that, no one has skin in the game.