© Pam Fray A statue of Old Father Time in Sandringham, Norfolk,
U.K. Getting older: it's a common human obsession, from surgery
to lift saggy skin to games that promise to keep the brain
flexible. In the larger natural world, though, getting older
takes many forms -- and scientists are beginning to peer more
deeply into the mysterious changes to an organism's biology as
it ages. Any evolutionary biologist will say that senescence --
a rise in mortality and a physical deterioration with age -- is
based on the concept of evolutionary fitness, the ability to
survive and reproduce. The individuals who reproduce copies of
their genes the most win the evolutionary game. If mutations
arise that shorten lifespan at older ages, but help younger
individuals, those mutations would get passed along. As the
theory goes, there should be a whole bunch of mutations that
affect later stages in life. "As humans get older, they are less
able to reproduce," said Shripad Tuljapurkar , a biologist at
Stanford University. "So the v