We discuss the Carter's formula about the mankind evolution probability
following the derivation proposed by Barrow and Tipler. We stress the relation
between the existence of billions of galaxies and the evolution of at least one
intelligent life, whose living time is not trivial, all over the Universe. We
show that the existence probability and the lifetime of a civilization depend
not only on the evolutionary critical steps, but also on the number of places
where the life can arise. In the light of these results, we propose a stronger
version of Anthropic Principle.