It's an uninformative prior (https://en.wikipedia.org/wiki/Prior_probability#Uninformative_priors https://en.wikipedia.org/wiki/Prior_probability#Uninformativ..

It's an uninformative prior (https://en.wikipedia.org/wiki/Prior_probability#Uninformative_priors https://en.wikipedia.org/wiki/Prior_probability#Uninformativ...). Meaning it's the best estimate you can make, if you don't have any additional information about the problem. Obviously we have a lot of additional information on human lifespans, which allows us to build a more accurate probability distribution. Also see my comment above.