Some genes allow for longer life than other genes. Some
creatures have genes that program them for death in days. Other
creatures are programmed to live for decades and do so if they
manage to escape catastrophe. Genetic evolution produced species
with longer normal life spans. A creature that lived a little
longer than others within its species allowed for a gene
mutation that produced this longer life. Eventually, those
within a species with longer-life genes became dominant within
their species. Some creatures were better able to defend
themselves, like tigers through their size and strength, or
humans by their adaptability, or turtles with their tough shell.
These creatures have genes developed across a great span of time
that give them a normally longer life than that of smaller,
weaker and more vulnerable creatures. Small birds that can
defend themselves by flying away from danger have genes that
give them a normal life of a decade or more. Mice, on the
otherhand, cannot escape by flying away and die of