A weakness of exogenous zeitgebers ?

-Doesn't have the same effect in all environment -Expdrience of peopel who live in places where there is very little darkness in summer and very little light in the winter tell a different story to the usual narrative -For instance, people who live in the artic cicle, ,like the Inuits of Greenland, have similar sleep patterns all year round, desptite spending around 6 months in almsot total darkness -Suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light