  For a subshift over a finite alphabet, a measure of the complexity of the
system is obtained by counting the number of nonempty cylinder sets of length
$n$. When this complexity grows exponentially, the automorphism group has been
shown to be large for various classes of subshifts. In contrast, we show that
subquadratic growth of the complexity implies that for a topologically
transitive shift $X$, the automorphism group $\Aut(X)$ is small: if $H$ is the
subgroup of $\Aut(X)$ generated by the shift, then $\Aut(X)/H$ is periodic.
