  At any moment in time, evolution is faced with a formidable challenge:
refining the already highly optimised design of biological species, a feat
accomplished through all preceding generations. In such a scenario, the impact
of random changes (the method employed by evolution) is much more likely to be
harmful than advantageous, potentially lowering the reproductive fitness of the
affected individuals. Our hypothesis is that ageing is, at least in part,
caused by the cumulative effect of all the experiments carried out by evolution
to improve a species' design. These experiments are almost always unsuccessful,
as expected given their pseudorandom nature, cause harm to the body and
ultimately lead to death. On the other hand, a small minority of experiments
have positive outcome, offering valuable insight into the direction evolution
should pursue. This hypothesis is consistent with the concept of "terminal
addition", by which nature is biased towards adding innovations at the end of
development. From the perspective of evolution as an optimisation algorithm,
ageing is advantageous as it allows to test innovations during a phase when
their impact on fitness is present but less pronounced. Our inference suggests
that ageing has a key biological role, as it contributes to the system's
evolvability by exerting a regularisation effect on the fitness landscape of
evolution.
