Since God is good and mortal life has a purpose, it seems reasonable to assume that the disposition of souls into bodies is not a random process; but that on the contrary part of some divine plan.
Therefore, the occurrence of genius is purposive - and this accounts for the destiny of each genius (the direction or path through life he ought to follow - whether or not he chooses to do so, or is prevented by circumstances and the choices of others).
Genius is not hereditary - or hardly-ever so. Rather, genius tends to be born into a family environment of high intelligence and abilities; presumably to provide sufficient nurturance of the necessary type.
The type of genius which God might be presumed to concern himself with, would be those Philosophical or Theological geniuses whose contribution is concerned with ultimate questions of the Human Condition:
In other words, the genius philosophers, theologians, prophets, mystics and saints: those who are intended (by God) to influence Man to (try to) work and live in accordance with God's hopes.
Yet all geniuses are also agents with free will and the capacity to choose; therefore they may (like Saruman) be sent to do a job which they themselves had volunteered and sworn to do - yet (like Saruman) become corrupted away from that job, and instead employ their great gifts against that job.
Thus, there is always the possibility of producing an evil genius instead of what was intended to be a good genius: the philosopher or theologian, the prophet or mystic gone-bad.
Such men are extremely dangerous - since the genius has manifold greater influence than ordinary men; and so we get the likes of Rousseau, Marx, Hitler, Lenin and Mao.
Or, a corrupt society may tend to take the output of a genius whose work included both good and bad - and may select and amplify the bad while neglecting the good.
And so we get the likes of Nietzsche, Heidegger, Wittgenstein; and also the pioneer 'liberal' biblical scholars and theologians over the past couple of centuries (but I am unsure of who are the major names in this field that are likely geniuses; probably Schleiermacher, David Friedrich Strauss, WE Channing; Charles Gore...).
Much the same applies to geniuses of the arts and sciences whose general cultural influence is (or is made) malign; the likes of James Joyce, Picasso, Schoenberg, Samuel Beckett...
It may well be that the rapid decline, and almost complete disappearance, of genius from the second half of the twentieth century was ultimately due to Western society becoming too hazardous a place for geniuses; a place where geniuses are too likely to go bad, to run off the rails.
What applies to geniuses of philosophy and theology applies even more powerfully to geniuses of art, science, politics and the rest of it - because when Man is aiming in the wrong direction then he cannot help but misuse his tools - and the more powerful the tools, the greater the potential for misuse.
So our civilisation stopped being allocated souls of genius.
For our own good.