As the hunter/gatherers which we evolved as, we were acutely aware of the seasons - the daylength would dictate activity, as would the temperature - we evolved to live within the "rhythms of nature". Biorhythms have been shown to be an accurate predictor of "off days", and is sufficiently accepted to be used by major airlines as a safety measure. If you have laying chooks on a commercial basis, it is usual practice to extend the natural daylight with artificial to keep their "day length" at around 17 hours, so that they're kept at their laying peak - commercially, after this "boosting" it is uneconomic to keep them beyond one season, so they're culled.
The thought that occurs to me is that this is precisely what we are doing to ourselves - forcing us to an artificial "clock" rhythm, rather than the natural rhythms of life - an area I feel needs more investigation!
