What would be the optimal human life span?

Added May 23, 2015

In years, what do you think would be the optimal life expentancy for humans? In other words, how long would you like human beings to live on average? This is a philosophical question. If humans had bodies designed to live much longer than they do now, the world and a human's life would be very different. Consider this in your answer.

For recent years in Swaziland life span is about 49 years (lowest) while in Japan is about 83 years (highest).