Last night, I was having a conversation with two friends about my recent travels when one mentioned how impressive it was that I didn’t seem to suffer from jet lag going either direction. I told them that it seems my sleep/wake cycles track the light very closely and so, wherever I am, I find my sleep schedule quickly adapts to match the relative light exposure. One friend, quite amused, quipped that my light-adaptive sleep behaviors would’ve served me quite well in the time of the caveman. To this I contested that it probably wouldn’t have mattered much in the time of the caveman, because access to long distance transit mechanisms was non-existent and thus they likely wouldn’t have had the means to experience many time zones anyways.