Recently I edited the entry on Cathemerality in Wikipedia, adding the Etymology section. The Ancient Greek roots of the term are: “κατα = kata, through, and ήμέρα = hemera, day. The combination yields ‘kathemeral’ or, in conventional English transliteration, ‘cathemeral,’ meaning ‘through the day’. Day refering to the full 24 hours from midnight to midnight. Cathemerality is defined by Tattersall as such: “The activity of an organism may be regarded as cathemeral when it is distributed approximately evenly throughout the 24 h of the daily cycle, or when significant amounts of activity, particularly feeding and/or traveling, occur within both, the light and dark portions of that cycle.” Tattersall, Ian (1987) “Cathemeral Activity in Primates: A Definition”. Folia primatol 49: 200-202.
Ian Tattersall speculates that the Lemur species he observed exhibiting cathemeral behaviour has evolved away from being nocturnal, and that cathemerality is an intermediate step toward becoming diurnal.
This makes me wonder about my own sleep schedule. Often I unintentionally sleep very little at night and wake up very, very early. Could sleep disorders actually be part of a normal spectrum of sleep? Are strange sleep schedules useful in a larger societal/evolutionary sense? It seems to me that our on the go lifestyles would benefit from 24 hours of evenly distributed activity.