mja...thank you for posting that study. There is clearly a lack of research on this phenomenon. I found another reference to this study which added one more sentence: "It seems likely that human hair follicles undergo cyclical activity and are influenced by environmental factors such as the photoperiod". It seems reasonable to assume that we humans would be as prone to shedding seasonally as other mammals. I think the variation in the length of daylight and temperature could certainly be factors, especially for those of us in the northern latitudes. Our circadium rhythm, controlled by the hypothalamus, is sensitive to the photoperiod. I have more than one autonomic-related disorder stemming from the hypothalamus, so I wouldn't be at all surprised if this comes into play with cyclical/seasonal shedding in my case.