  Although nuclear fission can be understood qualitatively as an evolution of
the nuclear shape, a quantitative description has proven to be very elusive. In
particular, until now, there exists no model with demonstrated predictive power
for the fission fragment mass yields. Exploiting the expected strongly damped
character of nuclear dynamics, we treat the nuclear shape evolution in analogy
with Brownian motion and perform random walks on five-dimensional fission
potential-energy surfaces which were calculated previously and are the most
comprehensive available. Test applications give good reproduction of highly
variable experimental mass yields. This novel general approach requires only a
single new global parameter, namely the critical neck size at which the mass
split is frozen in, and the results are remarkably insensitive to its specific
value.
