The backstory of Methuselah’s Children, by Heinlein, involves a foundation to promote human longevity. Among other activities it studies natural long-lifers, creating its research material by paying a bounty for marriages between people whose grandparents all lived 100 years or more.
Now here’s a stack of wacky ideas of mine.
Imagine that there exists, in a setting rather like that of Star Trek, a database of every human’s genome. An individual’s genome can be considered as a point in a space of billions of dimensions: four dimensions for each base, because there are five possibilities (A,T,G,C and deletion); but there is much redundancy in these data, because we necessarily have most genes in common, and the variable ones are somewhat correlated (one ethnic group differs from another in multiple genes).
My guess, untainted by knowledge of real population genetics, is that if you could plot all humanity in this space we’d all be close to a hyperplane of no more than twenty dimensions. A cartesian coordinate system is imposed on that subspace, and your state documents list your coordinates (in deciles rather than linearly).
Coming back to the Heinlein: An analogous foundation gives money to the first child born to any couple whose vectors (from the median) form an obtuse angle. Perhaps the goal is to promote interethnic friendship, or to study hybrid vigor, or to OMG DESTROY THE WHITE RACE, or simply to see what happens.