Hormones can surge and drop within minutes to direct many of our daily functions: sleep, digestion, reactions to stress. General hormone levels rise and fall slightly across the year as well. New work shows that the pattern has a seasonal memory of sorts, too, governed by a newly discovered internal clock. Each maximum or minimum causes hormone levels to rise or fall by several percent—small but significant—though often several months later. Credit: Accurat; Source: “Hormone Seasonality in Medical Records Suggests Circannual Endocrine Circuits,” by Avichai Tendler et al., in Proceedings of the National Academy of Sciences USA, Vol.