Now for this, you would need to take random couples from the whole population (so you'll need almost 4 billion cars for the first round), let them have sex in t

Now for this, you would need to take random couples from the whole population (so you'll need almost 4 billion cars for the first round), let them have sex in the car, then crash the car. You'd repeat with the survivors. I'd guess you'd get promising results quickly enough, half a dozen generation or something. And an interesting side effect would be that you'd solve the hunger and "human-made warming" in the world at the same time.