A theological-biological explanation of “the original sin’s transmission”

I think @Roger_Dimitrov makes a good point in another thread with the following comment:

In my view, the animal world ruled by evolutionary selfish interests is undoubtedly God’s creation.

But it is also undeniable that when it comes to humans called to share eternal divine life, these selfish evolutionary mechanisms become concupiscence, i.e.: propensity to sin, and this propensity becomes transmitted biologically by DNA replication.

So the problem remains:

Why does God let humans on earth with the propensity to sin?

To answer this question, it is crucial to keep in mind that “propensity or inclination to sin” is NOT sin.

What is more, “inclination to sin” can be used by God as a means for our salvation.

Because of the inclination to sin I carry inherited within me, I feel capable of “all the biggest crimes committed by the most wretched people”. Thereby I understand that I myself can also get damned. And this uncertainty pushes me to search certainty and security in the arms of my Father God: The “propensity to sin” I feel in me, becomes God’s ally after all.

Notice however that God did NOT create the first humans “with a propensity to sin”. As God made the first humans in the image of God, God ordered them to share eternal divine life, and endowed them with original grace capable of overcoming the selfish evolutionary mechanisms (as well as the illnesses and death) encoded in the sapiens DNA. “The propensity to sin” appears in human history concomitantly with the first sin.

In summary and paradoxically: Although God “hates sin”, God uses the “propensity to sin” as means to overcome sin:

“For [God’s] strength is made perfect in weakness […] when I am weak, then I am strong.” (2 Corinthians 12:9-10)