Great!, survival of the species is all that matters to you. Then, I suggest, that you can’t really be discussing sin or morality which concern interpersonal relations anyway. I’m surprised of that attitude after reading Harari’s Sapiens book.
Although, Dostoevsky didn’t originate the idea that “if god is dead, then all is permitted.” He mentioned it in “The Brothers Karamozoff.” A great book. It took off after that.