Variation in thyroid hormone levels can have profound effects on human behavior ranging from depressed-like states with pathologically reduced thyroid function to manic or even psychotic states with pathologically elevated thyroid hormone in individuals with hypo- and hyper-thyroidism, respectively.30–33 Similar behavioral changes occur in wild and domesticated animals with physiological seasonal variation in thyroid function, leading to adaptive changes in exploratory behavior in synchrony with environmental variables such as food availability and weather. This evidence concerns the gene TG and thyroid gland disorder.