Morality is Inherent... Consider This Analogy

First, let me preface by laying out the evolutionary explanation of morality in as simple terms as possible. Per evolutionary theory, life is about the survival of the fittest, which would seemingly rule out morality. Except, humans supposedly discovered that if they created some type of moral code and worked together to survive instead of fighting, they could survive and prosper even greater. However, when it comes down to the wire, to life and death, evolution tells us that the fittest will be those who survive, albeit by breaking moral codes and that those who die are losers, unfit.

Retired Marine Cpl. William 'Kyle' Carpenter receives the Medal of Honor for jumping on grenade to save the lives of his fellow marines

But let us consider the marine... The one that dives over a grenade in order to take the brunt of the blast and save his fellow comrades. By evolutionary theory, he died and was thus unfit. If he had run and saved himself instead, he would've been considered stronger, and more fit. His superior genes would've then been passed on to his children.

Can you bring yourself to call the self-sacrificial marine, 'unfit' or even 'loser'? He can no longer pass on his genes. This example may be modern but the principle goes back to ancient times. Why hasn't this unfit, weak gene died out? I believe it is because morality is inherent to all human beings.

I'd love to hear your thoughts whether you agree or disagree! Respectful debate is encouraged :)