“The most obvious physiological changes involved corticosteroids. In wild foxes, the levels of corticosteroids, hormones involved in adaptation to stress, rise sharply between the age of 2–4 months, reaching adult levels by 8 months of age. The domesticated wolves had their corticosteroid surge significantly later. The domesticated foxes have a much lower adrenal response to stress, and they have more serotonin in their blood.”