  Enhanced octupole collectivity is expected in the neutron-deficient Ge, Se
and Kr isotopes with neutron number $N \approx 40$ and has indeed been observed
for $^{70,72}$Ge. Shape coexistence and configuration mixing are, however, a
notorious challenge for theoretical models trying to reliably predict octupole
collectivity in this mass region, which is known to feature rapid shape changes
with changing nucleon number and spin of the system. To further investigate the
microscopic configurations causing the prolate-oblate-triaxial shape transition
at $A \approx 72$ and their influence on octupole collectivity, the rare
isotopes $^{72}$Se and $^{74,76}$Kr were studied via inelastic proton
scattering in inverse kinematics. While significantly enhanced octupole
strength of $\sim 32$ Weisskopf units (W.u.) was observed for $^{72}$Se, only
strengths of $\sim 15$ W.u. were observed for $^{74,76}$Kr. In combination with
existing data, the new data clearly question a simple origin of enhanced
octupole strengths around $N = 40$. The present work establishes two regions of
distinct octupole strengths with a sudden strength increase around the $A=72$
shape transitional point.
