  Although species longevity is subject to a diverse range of selective forces,
the mortality curves of a wide variety of organisms are rather similar. We
argue that aging and its universal characteristics may have evolved by means of
a gradual increase in the systemic interdependence between a large collection
of biochemical or mechanical components. Modeling the organism as a dependency
network which we create using a constructive evolutionary process, we age it by
allowing nodes to be broken or repaired according to a probabilistic algorithm
that accounts for random failures/repairs and dependencies. Our simulations
show that the network slowly accumulates damage and then catastrophically
collapses. We use our simulations to fit experimental data for the time
dependent mortality rates of a variety of multicellular organisms and even
complex machines such as automobiles. Our study suggests that aging is an
emergent finite-size effect in networks with dynamical dependencies and that
the qualitative and quantitative features of aging are not sensitively
dependent on the details of system structure.
