From Skin in the Game:
If humans were immortals, they would go extinct from an accident, or a gradual build-up of misfitness.
According to the Bible, this is, indeed, what happened. When humans could live almost 1000 years, we got so bad that God had to wipe the slate clean with the Flood. Something similar happened with the Tower of Babel. Lifespans had begun to shrink, but Shem still lived for 600 years and mankind had to be dispersed, or else the evil they would be able to accomplish would be considerable.
Continue reading Short Lives are a Grace