Preservation of the functional advantage of human time structure.

Upon exposure to sustained and synchronized diurnal activity, most human variables exhibit rhythms with a 24 h period. The best-fitting cosine curve to the data with a selected period (24 h) may yield parameters like acrophase (estimated peak time), amplitude, and mesor (rhythm adjusted mean). The sequential array of the rhythms' acrophases constructs the temporal order. Analyzing 168 different human rhythms revealed a time-dependent distribution with regard to the number of acrophases/h and to the clustering of variables according to function. Rhythms' amplitude/mesor ratios yielded a five modal distribution. The modes occurred at those clock times where repetitive habitual signals are anticipated. It is assumed that these specific features evolved to optimize the adaptive value of the temporal order.